GRUMBLES MARY (US)
DZIEDZIC RAFAL (US)
WIXTROM ALEX (US)
GANLEY EMILY (US)
NELSON YESSICA (US)
BOSLEY BETH (US)
EWING WILLIAM (US)
BORON SPECIALTIES LLC (US)
| CLAIMS 1. A composition comprising Li+ and a weakly-coordinating boron cluster anion. 2. The composition of claim 1, wherein the weakly-coordinating boron cluster anion comprises a formula of [B12Xx(OR)y]2-, wherein X is a halogen, R is selected from hydrogen, a branched or unbranched, saturated or unsaturated, substituted or unsubstituted alkyl, branched or unbranched saturated or unsaturated, substituted or unsubstituted silyl, or a substituted or unsubstituted aryl; and wherein y is an integer selected from 1, 2, 3, or 4 and x is an integer equal to 12 -y. 3. The composition of claim 1, wherein the weakly-coordinating boron cluster anion comprises a formula of [BnXx(OR)y]2-, wherein X is a halogen, R is selected from hydrogen, a branched or unbranched, saturated or unsaturated, substituted or unsubstituted alkyl, branched or unbranched saturated or unsaturated, substituted or unsubstituted silyl, or a substituted or unsubstituted aryl; and wherein n is an integer from 6 to 12, y is selected from 1, 2, 3, or 4 and x is an inter equal to n - y. 4. The composition of claim 1, wherein the weakly-coordinating boron cluster anion comprises a formula of [BnWmXx(OR)y]2-, wherein W is a heteroatom, X is a halogen, R is selected from hydrogen, a branched or unbranched, saturated or unsaturated, substituted or unsubstituted alkyl, branched or unbranched saturated or unsaturated, substituted or unsubstituted silyl, or a substituted or unsubstituted aryl; and wherein B and W form a polyhedron of n+m vertices where the sum of n+m is an integer from 6 to 12, y is selected from 1 , 2, 3, or 4 and x is an inter equal to n - y. 5. The composition of any one of claims 2-4, wherein X is Cl or Br. 6. The composition of any one of claims 2-4, wherein R is hydrogen, Me, Et, C3H5, C3H4O, C4H11, C6H13, TMS, -OCH2C6F5, or a polyethylene glycol. 7. The composition of claim 6, wherein X is Cl or Br. 8. The composition of any one of claims 1-7, wherein the composition is a solid. 9. The composition of claim 8, wherein the composition is a solid-state electrolyte. 10. The composition of any one of claims 1-7, wherein the composition further comprises a solvent and the weakly -coordinating boron cluster anion is dissolved within the solvent. 11. An electrochemical cell comprising an anode, a cathode, and an electrolyte comprising the composition according to claim 1. 12. The electrochemical cell of claim 11, wherein the electrolyte is a solid-state electrolyte. The electrochemical cell of claim 11, wherein the electrolyte is a liquid-state electrolyte. The electrochemical cell of any one of claims 11-13, wherein the weakly-coordinating boron cluster anion has a 2- → 1- redox potential of at least 3.0 V vs. Li/Li+. The electrochemical cell of any one of claims 11-14, wherein the weakly-coordinating boron cluster anion has a 1- → 0 redox potential of at least 3.5 V vs. Li/Li+. A composition of claim 1, wherein the composition comprises metal-coordinated weakly -coordinating boron cluster anions. The composition of claim 16, wherein the weakly-coordinating boron cluster anions comprise a fonnula of [B12(OR)12]2-, wherein R is selected from hydrogen, a branched or unbranched or a saturated or unsaturated, substituted or unsubstituted alkyl. The composition of claim 17, wherein R is the alkyl, wherein the alky l is optionally unsubstituted or wherein the alkyl is optionally substituted with an aryl, said aryl optionally substituted at one or more positions with a halogen. The composition of claim 18, wherein R is H or Me. The composition of any one of claims 16-19, wherein the weakly-coordinating boron cluster anions are coordinated with lithium. An electrochemical cell comprising an anode, a cathode, and an electrolyte comprising the composition according to claim 16. The electrochemical cell of claim 21, wherein the electrolyte is a solid-state electrolyte. |
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is related to, claims priority to, and incorporates herein by reference for all purposes U.S. Provisional Patent Application No. 63/350,759, filed June 9, 2022.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
This invention was made with government support under Grant Number GM124746, awarded by the National Institutes of Health, and Grant Number DE-SC0019381, awarded by the U.S. Department of Energy . The government has certain rights in the invention.
BACKGROUND OF THE INVENTION
The utility of weakly coordinating anions is ubiquitous across fields including stereoselective catalysis, polymerization initiation, electrochemistry and many more. Despite the wide breadth of applications, few weakly coordinating anions are synthetically tunable. Boron cluster-based weakly coordinating anions represent a class of anions that may be selectively altered to meet new challenges in application of this technology. However, many traditional scaffolds are expensive and difficult to scale. Therefore, new synthetic methods need to be developed to generate modular and scalable anions for enhanced efficacy of weakly coordinating anions.
BRIEF SUMMARY OF THE INVENTION
Boron cluster weakly-coordinating anions and methods of preparing the same are disclosed. One aspect of the invention provides for a composition comprising Li + and a weakly- coordinating boron cluster anion. In some embodiments, the weakly-coordinating boron cluster anion comprises a formula of [BnXx(OR) y ] 2- or a salt thereof, wherein X is a halogen, R is selected from hydrogen, a branched or unbranched, saturated or unsaturated, substituted or unsubstituted alkyl, branched or unbranched saturated or unsaturated, substituted or unsubstituted silyl, or a substituted or unsubstituted aryl and wherein n is an integer greater than or equal to 6, y is an integer selected from 1, 2, 3, or 4 and x is an inter equal to n - y. In some embodiments, the weakly -coordinating boron cluster anion comprises a formula of [B 12 X x (OR)y] 2- . Exemplary X include, Cl or Br. Exemplary R include, without limitation, Me, Et, C 3 H 5 , C 3 H 4 O, C 4 H 11 , C 6 H 13 , TMS, -OCH 2 C 6 F 5 , or a TEG (OC 7 O 3 H 15 ). In some mbodiments, the composition is a solid. In other embodiments, the composition is a solution comprising the weakly-coordinating boron cluster anion is dissolved within a solvent.
Another aspect of the invention provides for a composition comprising metal- coordinated weakly-coordinating boron cluster anion. The weakly-coordinating boron cluster anions may comprise a formula of [B 12 (OR) 12 ] 2- , wherein R is selected from hydrogen, a branched or unbranched or a saturated or unsaturated, substituted, or unsubstituted alkyl. Exemplary R include H or Me. In some embodiments, the weakly-coordinating boron cluster anions are coordinated with lithium.
Another aspect of the invention comprises an electrochemical cell comprising an anode, a cathode, and an electrolyte comprising any of the compositions described herein. In some embodiments, the electrolyte is a solid-state electrolyte. In other embodiments, the electrolyte is a liquid-state electrolyte. In some embodiments, the weakly-coordinating boron cluster anion has a 2- → I - redox potential of at least 3.0 V vs. Li/Li + and/or the weakly-coordinating boron cluster anion has a 1- → 0 redox potential of at least 3.5 V vs. Li/Li + .
These and other aspects of the invention are further described herein.
BRIEF DESCRIPTION OF THE DRAWINGS
Non-limiting embodiments of the present invention will be described by way of example with reference to the accompanying figures, which are schematic and are not intended to be drawn to scale. In the figures, each identical or nearly identical component illustrated is typically represented by a single numeral. For purposes of clarity, not every component is labeled in every figure, nor is every component of each embodiment of the invention shown where illustration is not necessary to allow those of ordinary skill in the art to understand the invention.
Figure 1: Schematic of the one-pot hydroxylation/chlorination procedure for synthesizing amino- and hydroxy-dodecaborate anions and their subsequent chlorinated derivatives.
Figure 2: Schematic for the alkylation of (NBu 4 ) 2 [B 12 Cl 9 (OH) 3 ] in dimethoxy ethane which requires a phase transfer agent (NBu 4 )Br to improve the solubility of the (NBu 4 ) 2 [B 12 Cl 9 (OH) 3 ] salt. The inset shows the electrospray ionization - mass spectrum of the alkylated products [B 12 Cl 9 (OC 5 H 11 ) 3 ] 2− [B 12 Cl 8 (OC 5 H 11 ) 3 (OH)] 2− which forms due to a [B 12 Cl 8 (OH) 4 ] 2− impurity.
Figure 3: The electrospray ionization - mass spectrum of B 12 C l 9 (O n Hex) 3 ] 2- and the differential scanning calorimetry of (NBu 4 ) 2 [B 12 C l 9 (O n Hex) 3 ] which shows melting at ~83 °C. Figure 4: Top, reaction of (NBu 4 ) 2 [B 12 Cl 9 (OH) 3 ] with KN(Si(CH 3 ) 3 )2 (KHMDS) and 1 -isopentylbromide. Middle, reaction of (NBu 4 ) 2 [B 12 Cl 9 (OH) 3 ] with (KHMDS). Bottom, reaction of (NBu 4 ) 2 [B 12 Cl 9 (OH) 3 ] with HN(Si(CH 3 ) 3 ) 2 (HMDS).
Figure 5: ESI spectrum of TBA 2 [B 12 Cl 10 (OH) 2 ].
Figure 6: ESI and 11 B NMR spectra and x-ray structure of TBA 2 [B 12 Cl 9 (OH) 3 ].
Figure 7: ESI, 11 B NMR, and 1 HNMR spectra of TBA 2 [B 12 Cl 9 (O(CH 2 ) 5 CH 3 ) 3 ].
Figure 8: 11 B NMR, and 1 HNMR spectra of C s2 [B 12 Cl 9 (O(CH 2 ) 5 CH 3 ) 3 ].
Figure 9: Cyclic voltammograms (left) and square wave voltammograms (right) of (NBu 4 ) 2 [B 12 Cl 9 (OH) 3 ] (top) and (NBu 4 )2[B 12 Cl 9 (O n Hex) 3 ] (bottom) in acetonitrile. 0.1 M (NBu 4 )[PF 6 ] supporting electrolyte 0.01 M analyte in acetonitrile, 0.1 V/s sweep rate. Glassy carbon working-electrode, Pt counter-electrode, Ag wire reference electrodes. All potentials are referenced to Fc/Fc + .
Figure 10: ESI and 1 HNMR spectra of C s2 [B 12 Cl 9 (O(CH 2 ) 2 CH 3 ) 2 ) 3 ] .
Figure 11: ESI and 1 HNMR spectra of C s2 [B 12 Cl 9 (OSi(CH 3 ) 3 ) 3 ].
Figure 12: Electrochemistry of Cs 2 [B 12 Cl 9 (OSi(CH 3 ) 3 ) 3 ].
Figure 13: ESI spectrum of B-O-Si crosslinked dodecaborates.
Figure 14: ESI spectrum and x-ray structure of TBA 2 [B 12 Br 9 (OH) 3 ].
Figure 15: 1 B NMR and 1 HNMR spectra of TBA 2 [B 12 Br 9 (OCH 2 CH 3 ) 3 ].
Figure 16: ESI spectrum of TBA 2 [B 12 Br 9 (O(CH 2 ) 5 CH 3 ) 3 ].
Figure 17: ESI spectrum of [B 12 (OH) x (OiPr) y H( 12-x-y )] 2- generated according to a first set of reaction conditions.
Figure 18: ESI spectrum of [B 12 (OH) x (OiPr) y H( 12-x-y )] 2- generated according to a second set of reaction conditions.
Figure 19: 11 B and 1 HNMR spectra of a prefunctionalized dodecaborate.
Figure 20: GC-MS, 11 B and 1 HNMR spectra of an expoxidated dodecaborate.
Figure 21: Panel A shows thermogravimetric analysis of Li 2 B 12 Cl 12 , Li 2 B 12 Cl 9 (OH) 3 and Li 2 B 12 Cl 9 (OCH 3 ) 3 and Panel B shows thermogravimetric analysis of Li 2 B 12 Br 12 , Li 2 B 12 Br 9 (OH) 3 and Li 2 B 12 Br 9 (OCH 3 ) 3 . Samples were heated at a rate of 10 °C/min under a constant flow of argon (200 mL/min).
Figure 22: A potential map showing the redox potentials (E1/2) for a series of weakly coordinating anion (WCA) clusters as disclosed herein.
Figure 23: Overlay of cyclic voltammograms for B 12 Cl 9 (OTEG) 3 2- where the upper potential limit is incrementally increased for 3.8 V to 4.4 V. Figure 24: A cyclic voltammogram of B 12 Cl 9 (OTEG) 3 2- for the w idest potential window (3.0V to 4.4V).
Figure 25: Overlay of cyclic voltammograms for TBA 2 B 12 Cl 9 (OH) 3 2- , TBA 2 B 12 Cl 9 (OMe) 3 2- , and TBA 2 B 12 Br 9 (OH) 3 2- clusters compared to TBA 2 B 12 Cl 12 2- , where the upper potential limit is 5 V and the potentials are vs Li/Li + .
Figure 26: Cyclic voltammograms ofB 12 Cl 12 2- and B 12 Cl 9 (OH) 3 2- collected at 100 mV/s scan rate in IM LiTFSI in 50:50 EC:DMC. Li was used as counter and reference electrodes. Glassy carbon was used as a working electrode. Overlayed for clarity.
Figure 27: 11 B{ 1 H} and 11 B NMR spectra of TBA 2 B 12 Cl 9 (OH) 3 used in cyclic voltammetry experiments. The 11 B{ 1 H} NMR spectrum of B 12 H 9 (OH) 3 2- is included for comparison.
Figure 28: Arrhenius plot of ionic conductivity demonstrating the weakly coordinating anions can function as solid-state electrolytes (SSEs).
DETAILED DESCRIPTION OF THE INVENTION
Disclosed herein are synthetically tunable weakly coordinating anions derived from boron cluster building blocks that are cheaper and more scalable than existing architectures. The utility of weakly coordinating anions is ubiquitous across fields including stereoselective catalysis, polymerization initiation, electrochemistry and many more. A series of facile, scalable synthetic methods have been developed and the presently disclosed methods overcome synthetic limitations and allow for the facile production of these tunable boron clusters at scale.
Weakly-coordinating boron cluster anions, such as [B 12 Cl 9 (OH) 3 ] 2- , may be produced on a scale as large as 100 g. Furtherdemonstrated herein is the capacity of functionalization to engender redox capabilities, providing a platform for the anions to be utilized in multiple oxidation states. The chemistry is compatible w ith cross-linking as well as the installation of polymerization handles. Overall, disclosed herein is a useful class of tunable, boron clusterbased anions that address the limitations of many weakly coordinating anions.
One aspect of the invention provides for mixed halogenated/hydroxylated boron cluster anions. These anions may be which can be amended with a variety of organic species (e.g., alkyl, aromatic, silyl) to create a diverse landscape of compounds with tunable properties. Additionally, the properties of the resulting anions can be tuned by altering the halogen type (Cl, Br, I, F). The boron clusters disclosed herein may be used to prepare compositions including Li + , or other metals, having tunable redox properties for use as electrolytes in electrochemical cells and batteries. Boron clusters comprise n number of boron atoms in a polyhedral form and contain (n + 1) skeletal bonding electrons that typically result in the formation of anions, such as closo type [BxHx] 2- anions where x is an integer greater than or equal to 6. In some embodiments, x is an integer from 6 to 12, including without limitation where x is 6, 10, or 12. These molecules exhibit unique bonding situations characterized by multicenter, two electron bonding and three- dimensional aromaticity and electron delocalization. These characteristics are believed to contribute to the high stability of these species.
Boron clusters may also comprise a heteroatom that replaces a boron atom in the polyhedral structure. These heteroboranes may be classified by formally converting the heteroatom to a BH X group having the same number of valence electrons. In some embodiments, the heteroboron cluster may comprise C, Si, Ge, or Sn in place of BH; N, P, As in place of BH 2 , or S or Se in place of BH 3 . In some embodiments, the heteroborane may be a carborane cluster where C replaces one or more BH groups.
In some embodiments, the compounds may be [BnX x (OR)y] 2- where the boron forms a polyhedron of n vertices where n is an integer greater than or equal to 6. In particular embodiments, n is an integer from 6 to 12, including where n is 6, 10, or 12. X is a halogen and R is selected from hydrogen, a branched or unbranched, saturated or unsaturated, substituted or unsubstituted alkyl, branched or unbranched saturated or unsaturated, substituted or unsubstituted silyl, or a substituted or unsubstituted aryl, and x and y are integers, the sum of which is n. X may be selected from Cl, Br, I, and F. Suitably, y may be selected from 1, 2, 3, or 4.
In some embodiments, the compounds may be [BnWmX x (OR)y] 2- where the boron and a heteroatom W form a polyhedron of n+m vertices where n and m an integer the sum of which is greater than or equal to 6. In particular embodiments, n+m is an integer from 6 to 12, including where n+m is 6, 10, or 12. Suitably, m is less than n. In some embodiments, m is 1. X is a halogen and R is selected from hydrogen, a branched or unbranched, saturated or unsaturated, substituted or unsubstituted alkyl, branched or unbranched saturated or unsaturated, substituted or unsubstituted silyl, or a substituted or unsubstituted aryl, x and y are integers, the sum of which is n-m. X may be selected from Cl, Br, I, and F. W may be selected from a heteroatom, such as C, Si, Ge, or Sn. Suitably, y may be selected from 1, 2, or 3.
In some embodiments, the compounds may be [B 12 X x (OR) y ] 2- where the boron atoms form a dodecaborate cluster with icosahedral symmetry, X is a halogen, R is selected from hydrogen, a branched or unbranched, saturated or unsaturated, substituted or unsubstituted alkyl, branched or unbranched saturated or unsaturated, substituted or unsubstituted silyl, or a substituted or unsubstituted aryl, and x and y are integers, the sum of which is 12. X may be selected from Cl, Br, I, and F. The integer x may be selected from 9, 10, and 11. The integer y may be selected from 1, 2, or 3. In some embodiments, R is hydrogen and may be prepared by the one-pot synthesis methods described herein.
In some embodiments, the compounds may be [B 12 (OR) 12 ] 2- , wherein R is selected from hydrogen, a branched or unbranched or a saturated or unsaturated, substituted or unsubstituted alkyl. In some embodiments, R is the alkyl, wherein the alkyl is optionally unsubstituted or wherein the alkyl is optionally substituted with an ary l, said aryl optionally substituted at one or more positions with a halogen.
Exemplary compounds of the present disclosure include [B 12 Cl 1 (OH) 11] 2- , [B 12 Cl 2 (OH) 10 ] 2- , [B 12 Cl 3 (OH) 9 ] 2- , [B 12 Br 1 (OH) 11 ] 2- , [B 12 Br 2 (OH) 10 ] 2- , [B 12 Br 3 (OH) 9 ] 2- , [B 12 F 1 (OH) 11 ] 2- , [B 12 F 2 (OH) 10 ] 2- , [B 12 F 3 (OH) 9 ] 2- , [B 12 I 1 (OH) 11 ] 2 --, [B 12 l 2 (OH) 10 ] 2- - ,[B 12 l 3 (OH) 9 ] 2- , [B 12 Cl 11 (OH)] 2- , [B 12 Br 11 (OH)] 2 --, [B 12 Cl 10 (OH) 2 ] 2- , [B 12 Br 9 (OH) 3 ] 2- , [B 12 Br 9 (OCH 3 ) 3 ] 2 --, [B 12 Cl 9 (OH) 3 ] 2 --, [B 12 Cl 9 (OCH 3 ) 3 ] 2- -, [B 12 Cl 9 (OTMS) 3 ] 2 --,
[B 12 Cl 9 (OBenzF 5 ) 3 ] 2- , [B 12 C l 9 (OC 3 H 5 ) 3 ] 2- , [B 12 Br 9 (O-ethyl) 3 ] 2- , [B 12 Cl 9 (OTEG) 3 ] 2 --,
[B 12 Br 10 (OH) 2 ] 2- , or [B 12 (OCH 3 ) 12 ] 2- .
Halogenation of the unfunctionalized B-H vertices of a [B n H n ] 2- cluster, such as [B 12 H 12 ] 2- , or [B n W m H n ] 2- ' cluster delocalizes the negative charge of anion and increases the oxidative stability of the anions. As a result, compounds of formula [B n X x (OR)y] 2- ', such as [B 12 Cl 9 (O H ) 3 ] 2- , or [B n W m X x (OR)y] 2- are amenable for use in ionic liquids. Moreover, the weakly coordinating anions have up to 4 hydroxyl groups that can be further functionalized. This allows for the tailoring of the anions and melting point for ionic liquids and redox properties for electrolytes.
In some embodiments, R is an organic species and may be prepared by the functionalization methods described herein. Suitably, R may be selected from a branched or unbranched, saturated or unsaturated, substituted or unsubstituted alkyl, branched or unbranched saturated or unsaturated, substituted or unsubstituted silyl, or a substituted or unsubstituted aryl. In order to create a weakly coordinating anionic matrix for ionic liquid applications, the anisotropy of the dodecaborate anion may be increased by appending organic species, such as alkyl groups, to the boron cluster through B-O-X linkages, where X is C, P, S, N, Al, B, Si, a transition metal, an alkali, or an alkali earth metal.
In some embodiments, the weakly coordinating boron cluster anion may be coordinated with a metal. In some embodiments the metal may be zinc or nickel. In one embodiment the metal is lithium. Exemplary metal-coordinated weakly coordinating boron cluster anions of the present disclosure include Li 2 [B 12 (OCH 3 ) 12 ], Li 2 [B 12 ( O CH 2 CH 3 ) 12 ], Li 2 [B 12 Cl 9 (OTEG) 3 ] and Li 2 [B 12 Cl 9 (OH) 3 ].
In some embodiments, the composition is solid. In some embodiments, the composition is a solid-state electrolyte. In one embodiment, the composition may be used to achieve room
5 temperature ionic conductivity. In one embodiment, the composition may be incorporated into an electrochemical cell with an anode, cathode, and an electrolyte. In one embodiment the electrochemical cell is a battery. In another embodiment, the battery may be an all-solid-state battery (ASSB). In one embodiment, the composition is used to achieve room temperature conductivity of lithium ions.
10 In some embodiments the composition may undergo a 1 electron, 1 electron, or 3 electron redox reaction. In some embodiments the redox potentials are tunable. Perfunctionalized dodecaborates can exhibit reversible oxidation events corresponding to the 2-/1- and 1-/0 oxidation states. For perhalogenated [ B 12 X 12 ] 2- clusters, the oxidation potential for the 2-/1- redox couple shifts to less positive potentials as X = I > Br > Cl > F. This shift
15 in redox potential is attributed to a combination of o-withdrawing effect and -backbonding of the p-orbitals of the X substituent to the boron cluster cage. Similarly, [ B 12 (O R) 12 ] 2- (R = alkyl or benzyl) species have much lower oxidation potentials due to increased -backbonding of the oxy gen lone pairs and diminished o-withdrawing effects due to the presence of the R group.
In some embodiments the redox potentials range from -1.0 to 6.0V versus Li/Li + . In
20 other embodiments the redox potentials range from 2.0V to 6.0V versus Li/Li 1 . In one embodiment the composition has a 2- to 1- redox potential of at least 2.0V, 2.1V, 2.2V, 2.3V, 2.4V, 2.5V, 2.6V, 2.7V, 2.8V, 2.9V, 3.0V, 3.1V, 3.2V, 3.3V, 3.4V, 3.5V, 3.6V, 3.7V, 3.8V, 3.9V, 4.0V, 4.1V, 4.2V, 4.3V, 4.4V, 4.5V, 4.6V, 4.7V, 4.8V, 4, ,9V, 5.0V. 5.1V, 5.2V, 5.3V, 5.4V, 5.5V, 5.6V, 5.7V, 5.8V, 5.9V or 6.0V versus Li/Li + . In another embodiment, the
25 composition has a 1- to 0 redox potential of at least 3.5V 3.6V, 3.7V, 3.8V, 3.9V, 4.0V, 4.1V, 4.2V, 4.3V, 4.4V, 4.5V, 4.6V, 4.7V, or 4.8V versus Li/Li + .
In other embodiments, the composition is soluble in a solvent. In some embodiments the solvent is aqueous. In other embodiments the solvent is non-aqueous. In some embodiments the solvent may include acetonitnle, ethyl acetate, methanol, ethanol, isopropanol, and
30 hexanes.
The term “alkyl” as contemplated herein includes a straight-chain or branched hydrocabon radical in all of its isomeric forms, such as a straight or branched group of 1-12, 1- 10, or 1-6 carbon atoms, referred to herein as C1-12 alkyl, C1-10 alky l, and C1-6 alkyl, respectively. In some embodiments, the alkyl may be unsaturated and, accordingly, may be an alkenyl or alkynyl. The term “alkenyl” as used herein refers to an unsaturated straight or branched hydrocarbon having at least one carbon-carbon double bond, such as a straight or branched group of 2-12, 2-10, or 2-6 carbon atoms, referred to herein as C 2-12 alkenyl, C 2-10 alkenyl, and C 2-6 alkenyl, respectively. The term “alkynyl” as used herein refers to an unsaturated straight or branched hydrocarbon having at least one carbon-carbon triple bond, such as a straight or branched group of 2-12, 2-10, or 2-6 carbon atoms, referred to herein as C 2-12 alkynyl, C 2-10 alkynyl, and C 2-6 alkynyl, respectively.
Unless specified otherwise, the alkyl may be substituted at one or more carbon positions with, for example, halogen, azide, alkyl, aralkyl, alkenyl, alkynyl, cycloalkyl, hydroxyl, alkoxyl, amino, nitro, sulfhydryl, imino, amido, carboxylic acid, -C(O)alkyl, -CChalkyl, carbonyl, carboxyl, alkylthio, sulfonyl, sulfonamido, sulfonamide, ketone, aldehyde, ester, heterocyclyl, aryl or heteroaryl moieties.
The term “aryl” is art-recognized and refers to a carbocyclic aromatic group. Representative aryl groups include phenyl, naphthyl, anthracenyl, and the like. The term “aryl” includes polycyclic ring systems having two or more carbocyclic rings in which two or more carbons are common to two adjoining rings (the nngs are “fused rings”) wherein at least one of the rings is aromatic and, e.g., the other ring(s) may be cycloalkyls, cycloalkenyls, cycloalkynyls, and/or aryls. Unless specified otherwise, the aromatic ring may be substituted at one or more ring positions with, for example, halogen, azide, alkyl, aralkyl, alkenyl, alkynyl, cycloalkyl, hydroxyl, alkoxyl, amino, nitro, sulfhydryl, imino, amido, carboxylic acid, - C(O)alkyl, -CChalkyl, carbonyl, carboxyl, alkylthio, sulfonyl, sulfonamido, sulfonamide, ketone, aldehyde, ester, heterocyclyl, aryl or heteroaryl moieties, -CF 3 , -CN, or the like. In certain embodiments, the aromatic ring is substituted at one or more ring positions with halogen, alkyl, hydroxyl, or alkoxyl. In certain other embodiments, the aromatic ring is not substituted, i.e., it is unsubstituted. In certain embodiments, the aryl group is a 6-10 membered ring structure.
The term "silyl" is art-recognized and refers to a group -SiR 3 where each R may be independently selected from hydrogen or a substituted or unsubstituted, branched or unbranched, saturated or unsaturated alkyl.
The term “haloalkyl” refers to an alkyl group that is substituted with at least one halogen. For example, -CH 2 F, -CHF 2 , -CF 3 , -CH 2 CF 3 , -CF 2 CF 3 , and the like.
The term “heteroalkyl” as used herein refers to an “alkyl” group in which at least one carbon atom has been replaced with a heteroatom (e.g., an O, N, or S atom). One type of heteroalkyl group is an “alkoxyl” group. The term “cycloalkyl” refers to a monovalent saturated cyclic, bicyclic, or bridged cyclic (e.g., adamantyl) hydrocarbon group of 3-12, 3-8, 4-8, or 4-6 carbons, referred to herein, e.g., as “C4-8-cycloalkyl,” derived from a cycloalkane. Unless specified otherwise, cycloalkyl groups are optionally substituted at one or more ring positions with, for example, alkanoyl, alkoxy, alkyl, haloalkyl, alkenyl, alkynyl, amido, amidino, amino, aryl, arylalkyl, azido, carbamate, carbonate, carboxy, cyano, cycloalkyd, ester, ether, formyl, halogen, haloalkyl, heteroaryl, heterocyclyl, hydroxyl, imino, ketone, nitro, phosphate, phosphonato, phosphinate, sulfate, sulfide, sulfonamido, sulfonyl or thiocarbonyl. In certain embodiments, the cycloalkyl group is not substituted, i.e., it is unsubstituted.
The term “cycloalkylene” refers to a diradical of a cycloalkyl group.
The term “partially unsaturated carbocyclyl” refers to a monovalent cyclic hydrocarbon that contains at least one double bond between ring atoms where at least one ring of the carbocyclyl is not aromatic. The partially unsaturated carbocyclyl may be characterized according to the number of ring carbon atoms. For example, the partially unsaturated carbocyclyl may contain 5-14, 5-12, 5-8, or 5-6 ring carbon atoms, and accordingly be referred to as a 5-14, 5-12, 5-8, or 5-6 membered partially unsaturated carbocyclyl, respectively. The partially unsaturated carbocyclyl may be in the form of a monocyclic carbocycle, bicyclic carbocycle, tricyclic carbocycle, bridged carbocycle, spirocyclic carbocycle, or other carbocyclic ring system. Exemplary partially unsaturated carbocyclyl groups include cycloalkenyl groups and bicyclic carbocyclyl groups that are partially unsaturated. Unless specified otherwise, partially unsaturated carbocyclyl groups are optionally substituted at one or more ring positions with, for example, alkanoyl, alkoxy, alkyl, haloalkyl, alkenyl, alkynyl, amido, amidino, amino, aryl, arylalkyl, azido, carbamate, carbonate, carboxy, cyano, cycloalkyl, ester, ether, formyl, halogen, haloalkyl, heteroaryl, heterocyclyl, hydroxyl, imino, ketone, nitro, phosphate, phosphonato, phosphinato, sulfate, sulfide, sulfonamido, sulfonyl or thiocarbonyl. In certain embodiments, the partially unsaturated carbocyclyl is not substituted, i.e., it is unsubstituted.
The terms “heterocyclyl” and “heterocyclic group” are art-recognized and refer to saturated, partially unsaturated, or aromatic 3- to 10-membered ring structures, alternatively 3- to 7-membered rings, whose ring structures include one to four heteroatoms, such as nitrogen, oxy gen, and sulfur. The number of ring atoms in the heterocyclyl group can be specified using 5 Cx-x nomenclature where x is an integer specifying the number of ring atoms. For example, a C3-7 heterocyclyl group refers to a saturated or partially unsaturated 3- to 7-membered ring structure containing one to four heteroatoms, such as nitrogen, oxygen, and sulfur. The designation “C3-7” indicates that the heterocyclic ring contains a total of from 3 to 7 ring atoms, inclusive of any heteroatoms that occupy a ring atom position.
The terms “amine” and “amino” are art-recognized and refer to both unsubstituted and substituted amines, wherein substituents may include, for example, alkyl, cycloalkyl, heterocyclyl, alkenyl, and aryl.
The terms “alkoxyl” or “alkoxy” are art-recognized and refer to an alkyl group, as defined above, having an oxygen radical attached thereto. Representative alkoxyl groups include methoxy, ethoxy, tert-butoxy and the like.
An “ether” is two hydrocarbons covalently linked by an oxygen. Accordingly, the substituent of an alkyl that renders that alkyl an ether is or resembles an alkoxyl, such as may be represented by one of -O-alkyl, -O-alkenyl, -O-alkynyl, and the like.
An “epoxide” is a cyclic ether with a three-atom ring typically include two carbon atoms and whose shape approximates an isosceles triangle. Epoxides can be formed by oxidation of a double bound where the carbon atoms of the double bond form an epoxide with an oxygen atom.
The term “carbonyl” as used herein refers to the radical -C(O)-.
The term “carboxamido” as used herein refers to the radical -C(O)NRR', where R and R' may be the same or different. Rand R' may be independently alkyl, aryl, arylalkyl, cycloalkyl, formyl, haloalkyl, heteroaryl, or heterocyclyl.
The term “carboxy” as used herein refers to the radical -COOH or its corresponding salts, e g. -COONa, etc.
The term “amide” or “amido” as used herein refers to a radical of the form - R 1 C(O)N(R 2- )-, -R 1 C(O)N(R 2 )- R 3 -, -C(O)N R 2- R 3 , or -C(O)NH 2 , wherein R 1 , R 2- and R 3 are each independently alkoxy, alkyl, alkenyl, alkynyl, amide, amino, aryl, arylalkyl, carbamate, cycloalkyl, ester, ether, formyl, halogen, haloalkyl, heteroaryl, heterocyclyl, hydrogen, hydroxyl, ketone, or nitro.
Salt of the compounds disclosed herein are also provided for. Suitably, the salt may be prepared from a mixture of the anions described herein with counter cations, such as alkali metals, alkali earth metals, protons, or organic cations, including organic cations suitable for use with an ionic liquids In some embodiments, the cations may be TBA + , Cs + , and the like.
To overcome the limitations of the art, the present technology is a large scale, one-pot synthesis of [B n Xx(OH) y ] 2- or [B n W m X x (OH) y ] 2- , such as [B 12 X x (OH) y ] 2- or [B 12 Cl 9 (OH) 3 ] 2- and the like, that serves as a versatile precursor in ionic liquids, electrolytes, flow-batteries, and weakly coordinating anions. Referring to Fig. 1, a scheme for preparing [B 12 X x (OH) y ] 2- is disclosed. Beginning from a [B12H12] 2- ’ dodecaborate cluster, the cluster may be hydroxylated by reacting the cluster in the presence an acid under conditions suitable for preparing the [B 12 H x (OH) y ] 2- . As illustrated in Fig. 1, the degree of hydroxylation may be controlled by reacting the cluster with an effective amount of an acid, such as H2SO4. As demonstrated in the Examples, the use of 26% H2SO4 results in the monohydroxylated product, 44% H 2 SO 4 results in the dihydroxylated product, and 54% H2SO4 results in the trihydroxylated product.
Upon synthesis of the [ B 12 H 9 (OH) 3 ] 2- anions, isolating the dry salts for chlorination with SO 2 CI 2 was difficult. Attempts to precipitate the [ B 12 H 9 (OH) 3 ] 2- with various organic cations (HNEt3 + , NBu 4 + and MePPh3 + ) were unsuccessful. The presence of hydroxyl groups on the [ B 12 H 9 (OH) 3 ] 2- anion enables hydrogen bonding interactions that prevent precipitation of[ B 12 H 9 (OH) 3 ] 2- salts. The high solubility of [ B 12 H 9 (OH) 3 ] 2- in water makes the chlorination with SO 2 CI 2 tedious because residual water can cause degradation of SO 2 CI 2 . Despite the hazardous nature of Ch gas, CI 2 sources are often found in household items such as bleach and pool cleaners. In particular, hypochlorous acid (H0C1), the main active ingredient in bleach, decomposes to CI 2 gas and water in the presence of acid. Thus, addition of NaOC ( aq) to an acidic solution of [ B 12 H 9 (OH) 3 ] 2- creates CI 2 gas that reacts leads to chlorination of the[ B 12 H 9 (OH) 3 ] 2- anion. Figure 1. After chlorination, the [ B 12 CI 9 (OH) 3 ] 2- anion readily precipitates as HNBu3 + , NBu 4 + and MePPh3 + salts from the aqueous reaction medium.
The halogen of the [B 12 X 9 (OH) 3 ] 2- anion may be suitably prepared by halogen substitution. As demonstrated in the Examples, [ B 12Br 9 (OH) 3 ] 2- anions may be prepared by substitution of the halogen atoms. Suitably, [ B 12 CI 9 (OH) 3 ] 2- may be reacted with X2, where X is a non-Cl halogen, under conditions sufficient for substitution of Cl with X.
Once the [BnX x (OH) y ] 2-- or [B n W m X x (OH) y ] 2-- salts, such as [ B 12 CI 9 (OH) 3 ] 2- salts, were isolated, alkylation of the clusters using a superbasic KOH/DMSO mixture to deprotonate the hydroxyl groups could proceed. However, the alkylation reactions proceeded slowly and often did not produce fully alkylated products. This may be due to two factors: 1) the steric bulk of the chlorine atoms near the B-OH vertices inhibits Sn2 reactivity and 2) the high pKa of the B-OH group requires a superbasic reaction medium to produce a small amount of reactive [B 12 Cl 9 (OH) 2 O] 3- . The long reaction times and partial conversion prompted us to search for a better reaction system.
Attempts to use a stronger base such as K t BuO in refluxing DME yielded trace amounts of alkylated [ B 12 CI 9 (OH) 3 ] 2- . Using NaH as a strong, non-nucleophilic base in dimethoxy ethane (DME) to deprotonate the [ B 12 CI 9 (OH) 3 ] 2- was successful however the poor solubility of the [ B 12 CI 9 (OH) 3 ] 2- in organic solvents, along with the steric blocking, only afforded partially alkylated [B 12 Cl 9 (OH) 3 ] 2- . Analysis of the unsuccessful reactions revealed the presence of 1- hexene by GC-MS suggesting that that steric bulk surrounding the active B-O vertex causes competition between S n 2 and E2 when reacting with 1 -bromohexane. To remedy these issues, (NBu 4 )Br was used to overcome the poor solubility of [ B 12 CI 9 (OH) 3 ] 2- in organic solvents, Figure 2. This combination of additives allowed us to achieve complete alkylation within 14 hours, as opposed to the 7+ day alkylation in superbasic KOH/DMSO mixtures. Having developed a versatile method for synthesizing (NBu 4 ) 2 [B 12 Cl 9 (O n Hex) 3 ], the melting point of the salt was measured with differential scanning calorimetry and an optical melting point apparatus which showed melting occurring at ~83 °C, Fig. 3. In contrast, the monoalkoxylated (NBu 4 )2[B 12 Cl 11 (OR)] (R = propyl, octyl, or dodecyl) do not melt below 300 °C, which highlights the effect of appending multiple alkoxy groups to lower the melting poi •nt.14
While developing the alkylation procedure for [ B 12 CI 9 (OH) 3 ] 2- resolving the poor solubility of the [ B 12 CI 9 (OH) 3 ] 2- in organic solvents was attempted by using acetonitrile as a polar, aprotic solvent. Although acetonitrile readily dissolves [ B 12 CI 9 (OH) 3 ] 2- salts, it is not compatible with NaH due to reduction of the nitrile group its subsequent reaction with alkyl halides. Thus, potassium bis(trimethylsilyl)amide (KHMDS) was employed as a strong, non- nucleophilic base that is capable of deprotonating the BOH group without generating byproducts of acetonitrile reduction. Reaction of (NBu 4 )2[B 12 Cl 9 (OH) 3 ] with 1 -bromohexane and KHMDS in acetonitrile resulted in quantitative conversion of B-OH to B-OSi(CH 3 ) 3 groups, Figure 4. In contrast, reaction of (NBu 4 )2[B 12 Cl 9 (OH) 3 ] with KHMDS in acetonitrile without alkyl bromide led to partial silylation of the hydroxyl groups. This difference in reaction outcome suggested that formation of neutral HN(Si(CH 3 ) 3 ) 2 and (C 5 H 11 )N(Si(CH 3 ) 3 ) 2 , formed via deprotonation of B-OH groups and Sn2 alkylation with 1 -bromohexane respectively, act as the active silylation reagent. Indeed, reaction of (NBu 4 )2[B 12 Cl 9( OH) 3 ] with HN(Si(CH 3 ) 3 ) 2 in acetonitrile resulted in quantitative conversion of B-OH to B-OSi(CH 3 ) 3 groups.
The following representation of a boron cluster illustrates a numbering scheme for a B12 cluster.
In some embodiments, vertex Bl is B-NH 3 , vertices B2-B6 are B-H, and vertices B7- B12 are B-Cl. In some embodiments, vertex Bl is B-NH 3 , four of vertices B2-B6 are B-H, and the remaining vertices are B-Cl. In some embodiments, vertex Bl is B-NH 3 , three of vertices B2-B6 are B-H, and the remaining vertices are B-Cl or B-Br. In some embodiments, vertex Bl is B-NH 3 , three of vertices B2-B6 are B-H, for example vertices B3, B5, and B6 or symmetry equivalent thereof are B-H, and the remaining vertices are B-Cl or B-Br. In some embodiments, the vertices are all B-Cl or all B-Br.
In some embodiments, vertex Bl is B-OH and vertices B2-B12 are B-H. In some embodiments, vertex Bl is B-OH and vertices B2-B12 are B-Cl. In some embodiments, two vertices are B-OH, for example vertex B 1 and vertex B7, and remaining vertices are B-H. In some embodiments, two vertices are B-OH, for example vertex Bl and vertex B7, and remaining vertices are B-Cl. In some embodiments, three vertices are B-OH, for example vertices Bl, B7, and B9, and remaining vertices are B-H. In some embodiments, three vertices are B-OH, for example vertices Bl, B7, and B9 or symmetry equivalents thereof, and remaining vertices are B-Cl. In some embodiments, three vertices are B-OR, for example vertices Bl, B7, and B9 or symmetry equivalents thereof, where R = alkyl or other group as described herein, and remaining vertices are B-Cl. In some embodiments, three vertices are B- OR, for example vertices Bl, B7, and B9 or symmetry equivalents thereof, where R = trimethyl silyl, and remaining vertices are B-Cl.
In some embodiments, some of the vertices are B-OH, some of the vertices are B-OR, where R = alkyl, and the remaining vertices are B-H. The R group can be alkyl, functionalized alkyl, alkenyl, epoxide, TEG.
Another aspect of the invention provides for crosslinked dodecaborate groups. Suitably, the compound may be crosslinked by a B-O-X, such as a B-O-Si crosslinker. The crosslinked clusters may be prepared from the [ B n X x (OH)y] 2- or [B n W m X x (OH) y ] 2- anions disclosed herein by the Examples provided below. In some embodiments, the compound may be [(B 12 X 11 )- OSi(CH 3 ) 2 O-(B 12 X 11 )] 4- but higher order oligomers or polymers may be prepared. In some embodiments, X is selected from C, P, S, N, Al, B, Si, a transition metal, an alkali, or an alkali earth metal.
Another aspect of the invention provides for compounds of formula [B n (OH) x (OR)yH(n- x-y)] 2- or a salt thereof. Suitably, R may be a branched or unbranched, saturated or unsaturated, substituted or unsubstituted alkyl and n is an integer greater than or equal to 6, suitably from 6-12, x is an integer from 0-n, y is an integer from 0-n, and x + y is an integer from 1-n.
Another aspect of the invention provides for compounds of formula [B n (OR) n ] 2- or a salt thereof. Suitably, R may be a branched or unbranched, saturated or unsaturated, substituted or unsubstituted alkyl. In some embodiments, the alkyl is an unsaturated alkyl that may be further used to functionalize or react the [B 12 (OR) 12 ] 2- compounds, such as the alkenyl groups disclosed in the Examples. In some embodiments, the alkyl is a substituted alkyl that may be further used to functionalize or react the [B 12 (OR) 12 ] 2- compounds, such as the epoxidated groups disclosed in the Examples.
Anionic polyhedral borates are renowned for their ability to serve as robust, weakly coordinating anions. These properties make polyhedral borates to be used as components in ionic materials such as ionic liquids and solid electrolytes. In particular, persubstituted icosahedral borates, [B 12 R 12 ] 2- , are known for their electrochemical stability, stability to acids and bases, and weakly coordinating nature due to the delocalized 3-dimensional aromaticity. Despite their weakly coordinating nature, ionic liquids based on polyhedral boranes do not exhibit the low melting points such as those observed for bis(trifluorosulfonyl)imide or cyanimide containing ionic liquids.
The higher melting points of dodecaborate-based ionic liquids may be due to their dianionic (2-) charge and icosahedral symmetry. The dianionic charge of dodecaborate can lead to higher lattice energies when compared to the lattice energies of salts composed of singly -charged anions. One approach to reducing the Coulombic attraction between the cations and the dodecaborate anions is to appending a formally cationic functional group such as ammonium, sulfonium, or phophonium group to the dodecaborate which results in a charge- compensated monoanionic dodecaborates. Another strategy for lowering the melting point of dodecaborate-based salts is to install alkyl chains which are believed to disrupt crystal packing by increasing the structural anisotropy of the anion. Alternatively, dodecaborate-containing ionic liquids can be formed by using long-chain alkyl imidazolium cations to further disrupt crystal packing.
Halogenation of the exohedral B-H bonds to B-X bonds (X = F, Cl, Br, or I) is used to increase the chemical stability of the dodecaborate anions against oxidative degradation. Despite the body of work on chlorinated dodecaborates, only a handful of chlorination techniques are reported. Although chlorination of PBs using chlorine gas is simple, the corrosive nature of Ch gas requires specialized gas fittings and safety protocols that can discourage synthesis of unique chlorinated dodecaborates for new applications. Alternative chlorination methods use highly corrosive SbCl 5 as a chlorinating agent or use SO 2 CI 2 in refluxing acetonitrile to produce Ch gas in situ. 18 ’ 19 Furthermore, the products of acid catalyzed hydroxylation and amination of dodecaborate in aqueous media require extensive drying prior to using SO 2 CI 2 as a chlorinating agent. 20-,2-1
Unless otherwise specified or indicated by context, the terms “a”, “an”, and “the” mean “one or more.” For example, “a molecule” should be interpreted to mean “one or more molecules.”
As used herein, “about”, “approximately,” “substantially,” and “significantly” will be understood by persons of ordinary skill in the art and will vary to some extent on the context in which they are used. If there are uses of the term which are not clear to persons of ordinary skill in the art given the context in which it is used, “about” and “approximately” will mean plus or minus <10% of the particular term and “substantially” and “significantly” will mean plus or minus >10% of the particular term.
As used herein, the terms “include” and “including” have the same meaning as the terms “comprise” and “comprising.” The terms “comprise” and “comprising” should be interpreted as being “open” transitional terms that permit the inclusion of additional components further to those components recited in the claims The terms “consist” and “consisting of’ should be interpreted as being “closed” transitional terms that do not permit the inclusion additional components other than the components recited in the claims. The term “consisting essentially of’ should be interpreted to be partially closed and allowing the inclusion only of additional components that do not fundamentally alter the nature of the claimed subject matter.
All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.
All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein. Preferred aspects of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred aspects may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect a person having ordinary skill in the art to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.
EXAMPLES
Exemplarily dodecaborate-based weakly-coordinating anions and the preparation thereof are illustrated in the Examples that follow.
EXAMPLE 1:
TBA 2 [B 12 Cl 10( OH) 2 ]
2 Cs +
1
The ESI spectrum of TBA 2 [B 12 C1 10 (OH) 2 ] is shown in Fig. 5. In this example, the Bl and B7 vertices are B-OH while the remaining vertices are B-Cl.
TBA 2 [B12Cl 9 (OH) 3 ]
Conducted on 100 g scale
The ESI and 11 B NMR spectra and x-ray structure of TBA 2 [B 12 Cl 9 (OH) 3 ] are shown in
Fig. 6. In this example, the Bl, B7, and B9 vertices are B-OH while the remaining vertices are B-Cl TBA 2 [B 12 Cl 9 (O(CH 2 ) 5 CH 3 ) 3 ]
2 TBA- ? R “ | 2 '
DME W >l,
80 C { 14 h RO^XS^tlR
30% yield
The ESI, 11 B NMR, and 1 H spectra of TBA 2 [B 12 Cl 9 (O(CH 2 ) 5 CH 3 ) 3 ] are shown in Fig.
7. In this example, the Bl, B7, and B9 vertices are converted from B-OH to B-OR where R=n- hexyl, while the remaining vertices are B-Cl.
CS 2 [B 12 C1 9 (O(CH 2 ) 5 CH 3 ) 3 ] 1 1 B NMR, and 1 HNMR spectra of CS 2 [B 12 Cl 9 (O(CH 2 ) 5 CH 3 ) 3 ] are shown in Fig. 8. In this example, the Bl, B7, and B9 vertices are converted from B-OH to B-OR where R=hexyl, while the remaining vertices are B-Cl.
Cyclic Voltammetry of TBA 2 [B 12 C1 9 (OH) 3 ] and TBA 2 [B 12 C1 9 (O(CH 2 ) 5 CH 3 ) 3 ]
Electrochemical analysis of (NBu 4 ) 2 [B 12 Cl 9 (OH) 3 ] and (NBu 4 ) 2 [B 12 Cl 9 (O n Hex) 3 ] did not display any reduction waves corresponding to a 2-/3- reduction event, however an oxidation peak was observed at voltages greater than +1.1 V vs Fc/Fc + , Fig. 9. The oxidation of the [ B 12 CI 9 (OH) 3 ] 2- anion (+1.2 V vs Fc/Fc + ) is not reversible, as evidenced by the lack of a reduction wave on the reverse voltage scan. In contrast, the oxidation of the[B 12 Cl 9 (O n Hex) 3 ] 2- anion (+1.1 V vs Fc/Fc 1 ) is cathodically shifted by ~0.1 V and it is reversible, as evidence by the presence of a reduction wave on the reverse voltage scan. A second oxidation event corresponding to the 1-/0 oxidation is not observable under these conditions due to decomposition of the electrolyte above +1.8 V. The cathodic shift in the oxidation potential of (NBu 4 ) 2 [B 12 Cl 9 (O n Hex) 3 ], relative to (NBu 4 ) 2 [B 12 Cl 9 (OH) 3 ], is due to reduced o-withdrawing effects of the alkoxy group compared to a hydroxyl group. The high cathodic stability of the [B 12 Cl 9 (O n Hex) 3 ] 2- [B 12 Cl 9 (O n Hex) 3 ] 2- anions, along with the reversible oxidation of the [B 12 Cl 9 (O n Hex) 3 ] 2- anion, presents new opportunities for boron cluster-based electrolytes and flow-batteries. TBA 2 [B 12 Cl 9 (O(CH 2 ) 2 CH(CH 3 ) 2 ) 3 ] wn in Fig. 2 and Fig. 10 respectively. In this example, the Bl, B7, and B9 vertices are converted from B- OH to B-OR where R=(CH 2 )2CH(CH 3 )2, while the remaining vertices are B-Cl. TBA 2 [B 12 Cl 9 (OSi(CH 3 ) 3 ) 3 ] example, the Bl, B7, and B9 vertices are converted from B-OH to B-OR where R=TMS, while the remaining vertices are B-Cl. Cyclic Voltammetry of TBA 2 [B 12 Cl 9 (OSi(CH 3 ) 3 ) 3 ]
A cyclic voltammogram of [B 12 Cl 9 (OSi(CH 3 ) 3 ) 3 ] is shown in Fig. 12. The cyclic voltammogram was conducted using 0.1 M TBA[PF 6 ] supporting electrolyte, 0.01 M analyte in acetonitrile, 0. 1 V/s sweep rate with a glassy carbon working-electrode, Pt counter-electrode, and Ag wire reference electrode. All potentials are referenced to Fc/Fc+. Cross-linking via B-O-Si Bonds
HOTS
0.17 eq CH S CN SO C< 28 h
The ESI spectrum of B-O-Si crosslinked dodecaborates is shown in Fig. 13. In this example, two clusters are linked at the respective Bl vertices by an -O-Si-O- linker, while the remaining vertices are B-Cl.
TBA 2 [B 12 Br 9 (OH) 3 ]
OH
Br s
50% MeOH
50% H z SQ. t TBA-Br
The ESI spectrum and x-ray structure of TBA 2 [B 12 Br 9 (OH) 3 ] are shown in Fig. 14. In this example, the Bl, B7, and B9 vertices are converted B-OH and the remaining vertices are converted to B-Br.
TBA 2 [B 12 Br 9 (OCH 2 CH 3 ) 3 ]
The ESI spectrum of TBA 2 [B 12 Br 9 (O(CH 2 ) 5 CH 3 ) 3 ] is shown in Fig. 15. In this example, the Bl, B7, and B9 vertices are converted from B-OH to B-OR where R=ethyl, while the remaining vertices are B-Cl. TBA 2 [B 12 Br 9 (O(CH 2 ) 5 CH 3 ) 3 ]
The ESI spectrum of TBA 2 [B 12 Br 9 (O(CH 2 )sCH 3 ) 3 ] is shown in Fig. 16. In this example, the Bl, B7, and B9 vertices are converted from B-OH to B-OR where R=n-hexyl, while the remaining vertices are B-Br. [ B 12 (OH) x (O i Pr) y H( 12-x-y ]| 2-
ESI spectrum of [ B 12 (OH) x (O i Pr) y H( 12-x-y ]| 2- prepared with H2SO4 is shown in Fig. 17.
In this example, some of the vertices are converted to B-OR where R = isopropyl while the remaining vertices are B-H or B-OH. Under these conditions, a mixture was observed that includes x=l-6 and y=3-10.
ESI spectrum of [B 12 (OH) x (OiPr) y H( 12-x-y )] 2 p- repared with H3PO4 is shown in Fig. 18.
In this example, some of the vertices are converted to B-OR where R = isopropyl while the remaining vertices are B-H or B-OH. Under these conditions, a mixture was observed that includes x=0-2 and y=l-2. Perfunctionalized Clusters
GC-MS, 11 B and 1 H NMR spectra of a perfunctionalized dodecaborate [B 12 (OC 3 H 5 )] 2- are shown in Fig. 19. In this example, the dodecaborate cluster is functionalized with an alkene group. The B1-B12 vertices are converted from B-H to B-OR where R= — C 3 H 5
GC-MS, 11 B and 1 H NMR spectra of an epoxidated dodecaborate are shown in Fig. 20. In this example, the dodecaborate cluster is functionalized with an epoxide. The Bl -Bl 2 vertices are converted to B-OR where R= C— 3 H 5 O.
General Procedure
Hydroxylation:
C S2 B 12 H 12 (2 g, 5 mmol) and a dry stir bar were added to a clean, dry round bottom flash (150 mL) and the flask was placed into an ice bath. Under vigorous stirring, diluted sulfuric acid was added dropwise using an addition funnel (22 mL, 43% v/v for dihydroxylation and 54% v/v for trihydroxylation). The round bottom flask was moved to an oil bath and fitted with a reflux condenser. The bath was heated to 110°C and the reaction was allowed to reflux for 20 hours. Note: Conversion was monitored by 11 B NMR spectroscopy.
Halogenation:
Halogenation immediately followed hydroxylation and was conducted in the same reaction vessel.
Chlorination:
After allowing the reaction to cool to room temperature after hydroxylation, the reflux condenser was removed and an addition funnel was fitted onto the round bottom flask. All joints were heavily greased and a stopper was placed on top of addition funnel to avoid any gas release. Excess sodium hypochlorite (6%, 35 mmol, 7 equiv per cluster) was slowly added to the round bottom via addition funnel while the contents were stirred heavily. The reaction was allowed to proceed at room temperature for 2 hours. After 2 hours, the round bottom was heated to 60°C for 24 hours. The reaction progress was monitored by ESI-MS(-).
Cation exchange and work-up:
Unreacted chlorine was quenched with sodium sulfite until the reaction liquid was clear. Excess (2.2 equivalents per cluster) tetrabutylammonium bromide was dissolved in minimal water and added drop-wise to the reaction mixture. A white powder precipitated from solution and was collected via vacuum filtration. After 3 washes with water (10 mL), the product was collected and recrystallized from hot ethanol.
Bromination:
After allowing the reaction to cool to room temperature after hydroxylation, the reflux condenser was removed and the reaction was diluted by 50% using methanol. Under vigorous stirring at room temperature, bromine (5.0 mL, 0.2 mol, 40 equiv per cluster) was added to the mixture. The round bottom flask was re-fitted with the reflux condenser and the reaction was heated to 60°C for 48 hours. The reaction progress was monitored by ESI-MS(-).
Cation exchange and work-up:
Unreacted bromine was quenched with sodium thiosulfate until the reaction liquid was clear. The acid was quenched with calcium carbonate until pH strips indicated the neutral pH. The reaction mixture was then filtered under vacuum. The filtrate was subjected to rotary evaporation to remove methanol. After, excess (2.2 equivalents per cluster) tetrabutyl ammonium bromide was dissolved in minimal water and added dropwise to the reaction mixture. A white powder precipitated from solution and was collected via vacuum filtration. After 3 washes with water (10 mL), the product was collected and recrystallized from hot ethanol.
Alkylation:
Unless otherwise noted, the following procedure was used to alkylate the mixed halogenated/hydroxylated anions. To a dry, clean Schlenk flask, TBA 2 (B 12 X 9 -io(OH)2-3) (0.5 mmol), tetrabutyl ammonium iodide (0.7 mmol) and a stir bar were added. The flask was then brought into a glovebox and sodium hydride (5.0 mmol) and dried dimethoxyethane (5.0-10.0 mL) were added. The flask was stoppered and removed from the glovebox. After, the flask was placed into an oil bath and charged with alkyl halide (2.5 equiv per hydroxy). The oil bath was then heated to 80°C for 14 hours. Work-up:
After 14h, the flask was moved from the oil bath and into an ice bath. Excess sodium hydride was quenched by slowly adding methanol (25 mL) to the reaction mixture under stirring. Once all solids had dissolved and bubbles ceased to evolve, the flask was removed from the ice bath and solvent was removed under rotary evaporation. The solids were placed onto a filter and washed with hexanes (20 mL), sodium sulfite (5 M, 20 mL) and water (20 mL x 3). The product was then dissolved in dichloromethane (5.0 mL) and placed onto a silica plug. Pure product was eluted using a mixture (50:50 v/v) dichloromethane and acetone. Solvent was then removed under rotary evaporation. Depending on the alkyl chain, the product was recrystallized from either hot isopropanol or ethanol.
EXAMPLE 2
Halogenated dodecaborates [B 12 X 12 ] 2- (X= Cl, Br, I, F) are polyhedral boranes that can be produced from facile and scalable syntheses; however, generally low solubility of these salts limits widespread utility. Herein are presented a series of mixed halogenated dodecaborates. The present strategy allows for tuning of physical properties such as steric bulk, solubility and thermal stability of the anions. Coordination to both tetrabutylammonium (TBA + ) and lithium (Li + ) cations is demonstrated. Thermogravimetric analysis offers insights on the thermal stability of [B 12 X 9 (OR) 3 ] 2 -- anions. Finally, a preliminary assessment of solubility demonstrates enhanced solubility of [B 12 X 9 (OR) 3 ] 2w- salts over perhalogenated analogues.
Dodecaborate anions have a significant limitation of generally lower solubilities of [B 12 X 12 ] 2- salts compared to those of [HCB 11 H 11 ]-. Herein, the scope of accessible dodecaborate-based WCAs is augmented through a mixed hydroxylation and halogenation strategy. Through mixed halogenation a platform for tuning the solubility of the resulting salts is provided, circumventing this known limitation of dodecaborate anions. Importantly, alkoxylation offers further opportunities for steric blocking of hydroxyl oxygen while also allowing for enhanced modulation of stability and solubility. Coordination to both alkali metal lithium and organic cation tetrabutylammonium is demonstrated. Thermal stability profiles of the resulting salts is highlighted and preliminary evidence of enhanced solubility of mixed halogenated clusters over the corresponding perhalogenated analogues is provided.
After initial discovery of [B 12 X 12 ] 2-- , a number of early pioneers explored various methods to modify [B12H12] 2- : Specifically, Muetterties reported the hydroxylation of [B 12 H 12 ] 2 -- by heating N-methyl-2-pyrrolidinone in nitric acid. (Knoth, W. H ; Sauer, J. C.; England, D. C ; Heftier, W. R.; Muetterties, E. L. Chemistry of Boranes. XIX. 1 Derivative Chemistry of BioHio" 2- and B 12 H 12 -2 . J. Am. Chem. Soc. 1964, 86, 3973-3983.) Subsequent treatment of the product with NaOH yielded [B 12 Hm(OH) n ] 2- where m= 10-11 and n= 1-2. Decades later, a single-step hydroxylation in sulfuric acid was reported by Hawthorne and coworkers. This high yielding and efficient method offered a higher degree of specificity in hydroxyl addition leading to the isolation of [B 12 H m (OH) n ] 2- clusters where m= 8-11 and n= 1 - 4. The preparation reported by Hawthorne was used with slight modification (49% sulfuric acid was increased to 53%) to generate [B 12 H 9 (OH) 3 ] 2- (Scheme 1, see Synthesis below). (Peymann, T.; Knobler, C. B.; Hawthorne, M. F. A Study of the Sequential Acid-Catalyzed Hydroxylation of Dodecahydro-closo-dodecaborate(2-). Inorg. Chem. 2000, 39, 1163-1170) It should be noted that hydroxylation repeatably led to -5-10% [B 12 H8(OH)4] 2- by-product. This compound could be removed through column chromatography; however, for ease of subsequent scale-up the slight [B 12 H 8 (OH) 4 ] 2- - impurity in all subsequent reactions was retained.
Scheme 1: Schematic detailing the hydroxylation, halogenation, and alkoxylation of [B 12 X 12 ] 2- . In this example, the Bl, B7, and B9 vertices are converted to B-OH and to B-OR where R=methyl, while the remaining vertices are B-Cl or B-Br. Scheme 2: Schematic detailing the facile generation of Na2B 12 H 12 from the pyrolysis ofNaB 3 H 8 .
Following hydroxylation, [B 12 H 9 (OH) 3 ] 2- was subjected to either chlorination or bromination to yield [B 12 Cl 9 (OH) 3 ] 2- and [B 12 Br 9 (OH) 3 ] 2- , respectively. (Scheme 2, see Synthesis below) Perchlorination of [B 12 HI 2 ] 2- has been achieved through various preparations. First, Muetterties and coworkers heated Na 2 B 12 H 12 *2H 2 O in a silver-lined pressure vessel containing chlorine gas for 2 hr under autogenous pressure.( Knoth, W. H. ; Miller, H. C. ; Sauer, J. C.; Balthis, J. H.; Chia, Y. T.; Muetterties, E. L. Chemistry of Boranes. IX. 1 Halogenation of BioHio' 2- and B 12 H 12 ' 2- . Inorg. Chem. 1964, 3, 159-167.) Later, the method was improved by Uzun et al. who achieved perchlorination by bubbling chlorine gas into a solution of Na 2 B 12 Hi 2 for ~30 hr (Geis, V.; Guttsche, K ; Knapp, C.; Scherer, H.; Uzun, R. Synthesis and Characterization of Synthetically Useful Salts of the Weakly-Coordinating Dianion [B 12CI 12 ] 2-- . Dalton Trans. 2009, 15, 2649-2884). Finally, perhalogenation was achieved using thionyl chloride (SOCI 2 ) under refluxing in acetonitrile. An alternate approach utilizing sodium hypochlorite to generate Ch in situ was used in order to circumvent the need for a chlorine tank or highly corrosive SOCI2, significantly enhancing the safety and scalability of the reaction. Sodium hypochlorite was previously utilized to chlorinate the B-H bonds within tertiary amineboranes as outlined below:
Rate of chlorination increased with decreasing pH as formation of hypochi orous acid was determined to be the kinetically limiting step for monochlorination. A similar approach was applied by treating CS 2 B 12 H 9 (OH) 3 dissolved in sulfuric acid to dropwise addition of excess sodium hypochlorite (6%). Green gas (CI2) was observed upon addition of the sodium hypochlorite and the sealed vessel was allowed to stir at room temperature for two hours after which the temperature was increased to 60 °C. Following a 24 hr period, product was precipitated by addition of tetrabutylammonium bromide (TBA-Br), filtered and washed with water. Negative mode ESI(-) mass spectrometry of the isolated product was consistent with the formation of [B 12 Cl 9 (OH) 3 ] 2-- . Next, the isolated product was analyzed through 11 B NMR spectroscopic analysis. A singlet resonance was observed (-7.2 ppm) along with two overlapping resonances (-13.5 ppm and -15.2 ppm) with an integral ratio of 1 to 3 consistent with the expected splitting pattern for [B 12 Cl 9 (OH) 3 ] 2- (See Methods below). After, the nature of the cation was probed through 1 H and 13 C NMR spectroscopic analysis. A distinct singlet with an integration of 3 was observed in the 3 H NMR spectrum along with four multiplets in an integral ratio of 16:16: 16:24, indicating the [B 12 Cl 9 (OH) 3 ] 2- anion had been isolated as a TBA salt. Four resonances in the 13 CNMR spectrum corresponding to the TBA cation lend additional support to the formation of TBA 2 B 12 Cl 9 (OH) 3 (see Methods below). Finally, X-ray crystallography unequivocally confirmed the presence of TBA 2 B 12 Cl 9 (OH) 3 as well as the regioselectivity in hydroxyl placement which aligned well with previous hydroxylation reports. No evidence of cation coordination to the hydroxyl moiety is observed within the complex, suggesting the steric bulk of halogenation is sufficient to shield the oxygen atom from TBA + . Importantly, the reaction conditions could be applied to kilogram-scale chlorination at collaborator facilities, suggesting the facile and inexpensive preparation is amenable to industrially relevant quantities. Bromination of [B 12 Hb(OH) 3 ] 2- was achieved using a reported method with only slight modification (See Methods below) and the[B 12 Br 9 (OH) 3 ] 2- anion was also isolated as a TBA salt in order to provide a more consistent analysis of anionic properties.
Next, both TBA 2 B 12 Cl 9 (OH) 3 and TBA 2 B 12 Br 9 (OH) 3 were methylated in order to enhance the steric hindrance of the [B 12X 9 (014) 3 ] 2- scaffold and offer new opportunities for tuning of physical properties. Taking inspiration from reports for the peralkoxylation of [B 12 (OH) 12 ] 2- , TBA 2 B 12X 9 (OH) 3 was heated to 80 °C in 1 ,2-dimethoxy ethane (DME) with strong base, sodium hydride (NaH). After 5 min, the reaction vessel was charged with excess methyl iodide (CH 3 -I) and allowed to react. Masses consistent with full methylation of TBA 2 B 12 Cl 9 (OH) 3 were observed by negative mode ESI(-) mass spectrometry within 30 min. In addition, a distinct singlet was observed at 3.5 ppm in the 1 H NMR spectmm along with four multiplets in an integral ratio of 9: 16:16: 16:24, further suggesting full methylation to TBA 2 B 12 Cl 9 (OCH 3 ) 3 had occurred. Finally, five resonances were observed in the 13 C spectrum corresponding to four TBA cation resonances and one resonance corresponding to the methoxy 13 C. Methylation of TBA 2 B 12 Br 9 (OH) 3 was more sluggish, requiring 18 hours to reach full conversion by negative mode ESI(-) mass spectrometry. The slower kinetics associated with methylation of TBA 2 B 12 Br 9 (OH) 3 are likely the result sterically encumbering B-Br pentagonal belt surrounding the hydroxyl groups, limiting access to the methylating reagent. In addition to mass spectrometry, 3 H NMR and 13 C NMR spectroscopy confirmed full conversion to TBA 2 B 12 Br 9 (OCH 3 ) 3 (See Synthesis below).
After generation of TBA 2 B 12 X 9 (OR) 3 (X= Br, Cl and R= H, CH 3 ) salts, a resin- based cation exchange method was utilized to convert to the organic cation to lithium. Adapted from an elegant approach reported by Strauss and coworkers, TBA 2 B 12 X 9 (OR) 3 was dissolved in various mixtures of acetone, acetonitrile and methanol depending on the solubility of the given salt and passed through a column packed with Amberlyst-15 proton resin exchange beads (See Cation Exchange Procedures and Table 1 below and Ivanov, S. V.; Miller, S. M.; Anderson, O. P.; Solntsev, K.A: Strauss, S. H. Synthesis and Stability of Reactive Salts of Dodecafluoro- closo-dodecaborate(2-). J. Am. Chem. Soc. 2003, 125, 4694-4695.). The eluted solvent was dried in vacuo until an oily residue remained. The residue was dissolved in water and the pH was brought up to 7 using LiOH. After drying in vacuo, white powders were isolated. Complete cation exchange was first indicated by the facile dissolution of the isolated powders in water as all TBA 2 B 12 X 9 (OR) 3 salts were completely insoluble in aqueous media. Secondly, a singlet resonance at ~0.0 ppm was observed by 7 Li NMR spectroscopy for all cation-exchanged salts further suggesting the organic cation had been removed. 1 H NMR and 13 C NMR spectroscopy provided additional evidence that lithium salts had been isolated. No resonances were observed in the 1 HNMR spectra for both Li 2 B 12 Cl 9 (OH) 3 and Li 2 B 12 Br 9 (OH) 3 providing indirect verification of TBA removal. The 1 HNMR spectrum for Li 2 B 12 Cl 9 (OCH 3 ) 3 contained only a singlet resonance at 3.7 ppm which can be ascribed to the methoxy 1 H nuclei. Similarly, a single resonance at 54.6 ppm was observed by 13 C NMR and corresponds to the methoxy 13 C nuclei. As with Li 2 B 12 Cl 9 (OCH 3 ) 3 , the 1 HNMR and 13 C NMR Spectra of Li 2 B 12 Br 9 (OCH 3 ) 3 contained single resonances corresponding to methoxy at 3.7 ppm and 54.8 ppm, respectively (See Cation Exchange Procedures, below). These results highlight capacity ion exchange to dramatically alter the solubility properties of the anions and provides a useful path forward for many battery and Li-conductivity applications.
Next, the thermal stability of the library of mixed halogenated dodecaborates as lithium salts was analyzed using thermogravimetric analysis. In order to benchmark the stability, Li 2 B 12 Cl 12 and Li 2 B 12 Br 12 were prepared as control samples (See Synthesis below). As seen in Figure 21 A, the plot of weight (%) against temperature indicates that from 60 °C to 200 °C, 18% of the Li 2 B 12 Cl 12 sample weight is lost, suggesting three water molecules were coordinated to each lithium (See Thermogravimetric Analysis, below). As the temperature scans from 200 °C to 575 °C, no weight change is observed indicating Li 2 B 12 Cl 12 is thermally stable across this range. These results are in close agreement with the thermogravimetric analysis of CS 2 B 12 Cl 12 where no mass changes were observed between 180 °C and 600 °C. After 600 °C, decomposition of the sample and 85% mass loss was observed. Comparatively, a 14% dehydration was observed in the sample of Li 2 B 12 Cl 9 (OH) 3 , corresponding to only two water molecules per lithium, possibly due to coordination of the anion hydroxy groups to the alkali metal (Figure 21A). Elevating the temperature from 200 °C to 500 °C results in negligible weight change; however, after 500 °C, a rapid loss in 20% of the sample weight is observed suggesting mixed halogenation lowers the thermal stability of the anion scaffold. After initial dehydration corresponding to the loss of three water molecules per lithium, heated sample of Li 2 B 12 Cl 9 (OCH 3 ) 3 resulted in the most significant weight change profile as -10% loss is observed at just 250 °C (Figure 21 A,). Continued mass loss is observed as heating extends to 1000 °C resulting in an overall 80% reduction in sample weight. The significant impact of methylation upon anion stability could be the result of thermally induced, lithium chloride- catalyzed demethylation which was previously observed in aryl methyl ether substrates by Bei and coworkers under microwave conditions. The library of brominated lithium salts was analyzed by thermogravimetric analysis. Samples of Li 2 B 12 Br 12 , Li 2 B 12 Br 9 (OH) 3 and Li 2 B 12 Br 9 (OCH 3 ) 3 dehydrated by 8%, 15% and 11%, corresponding to the coordination of three, four and three water molecules to lithium, respectively (Figure 21 B). Heating Li 2 B 12 Br 12 beyond 200 °C resulted in no significant mass changes until 800 °C where 80% of the sample weight was lost. This remarkable stability is in close agreement with the thermogravimetric analysis of Cs2B 12 Br 12 where heating to 950 °C was required to induce decomposition. Heating Li 2 B 12 Br 9 (OH) 3 beyond 200 °C resulted in little change in weight until 500 °C, after which continuous mass loss was observed indicating Li 2 B 12 X 9 (OH) 3 salts have similar thermal stability when X= Cl and X= Br. Finally, continuous weight loss is observed in the thermogravimetric curve of Li 2 B 12 Br 9 (OCH 3 ) 3 across the thermal scan from 60 °C to 1000 °C suggesting thermally induced reactivity is likely occurring in heated samples of both L1 2 B12Cl 9 (OCH 3 ) 3 and Li 2 B 12 Br 9 (OCH 3 ) 3 (Figure 21 B). Overall, mixed halogenation lowers thermal stability when compared to perhalogenation; however, exceptional stability is still demonstrated, especially for Li 2 B 12 X 9 (OH) 3 salts which remain intact up to 500 °C. Importantly, halogen type (X= Cl or Br) did not substantially impact thermal stability and modulation of X could be used instead to modulate the stenc and solubility properties of the resulting salt.
Finally, a preliminary assessment of the solubility properties of anhydrous Li 2 B 12 Cl 12 , Li 2 B 12 Cl 9 (OH) 3 and Li 2 B 12 Cl 9 (OCH 3 ) 3 in acetonitrile, ethyl acetate, methanol, ethanol, isopropanol, and hexanes was completed. (See Assessment of Solubility and Table 2, below) Li 2 B 12 Cl 12 was insoluble in all solvents except ethyl acetate where partial solubility was observed. Li 2 B 12 Cl 9 (OH) 3 was insoluble in all solvents except ethyl acetate, ethanol and isopropanol where partial solubility was observed. The enhanced solubility could be a result of hydrogen bonding facilitated by hydroxylation of the cluster. In contrast to both Li 2 B 12 Cl 12 and Li 2 B 12 Cl 9 (OH) 3 , Li 2 B 12 Cl 9 (OCH 3 ) 3 was found to be insoluble only in hexanes. In all other solvents, partial or full solubility was observed indicating methylation affords significant enhancement to anion solubility which could be due to both enhanced intermolecular interactions (Van Der Waals and hydrogen bonding) as well as alterations to the polarity of the cluster. Computational modeling will be conducted in future studies in order to better understand the impact of mixed hydroxylation and halogenation upon solubility.
In conclusion, a series of [B 12 X 9 (OR) 3 ] 2- (X= Br, Cl and R= H, CH 3 ) WCAs is prepared from a mixed hydroxylation and halogenation strategy . A facile method for chlorination is disclosed herein utilizing sodium hypochlorite which enhances the usability and safety of the reaction by eliminating the need for a chlorine gas tank or highly corrosive SOCI 2 . This developed procedure was amenable to both mixed halogenation as well as perhalogenation, suggesting a wide array of dodecaborate substrates could be modified. Importantly, kilogramscale chlorination was demonstrated, suggesting these reaction conditions could be synthesized at industrially quantities. Coordination of all anions to both TBA + and Li + is demonstrated and thermogravimetric analysis of Li 2 B 12 Xs(OR) 3 salts was conducted. A reduced thermal stability was observed for both Li 2 B 12 Cl 9 (OH) 3 and Li 2 B 12 Br 9 (OH) 3 when compared to the perhalogenated analogues; however, both salts were stable up to exceptionally high temperatures (-500 °C). Onset of decomposition within Li 2 B 12 Cl 9 (OCH 3 ) 3 and Li 2 B 12 Br 9 (OCH 3 ) 3 salts was observed at -250 °C highlighting the impact enhanced organic character imparts upon anion stability. Finally, a preliminary assessment of the solubility 7 of Li 2 B 12 Cl 12 , Li 2 B 12 Cl 9 (OH) 3 and Li 2 B 12 Cl 9 (OCH 3 ) 3 in selected solvents was conducted. The least soluble salt was Li 2 B 12 Cl 12 followed by Li 2 B 12 Cl 9 (OH) 3 and then Li 2 B 12 Cl 9 (OCH 3 ) 3 , suggesting the proposed strategy was effective at enhancing anion solubility.
Materials:
All reagents were purchased from Sigma Aldrich, Strem Chemicals, Chemlmpex, Oakwood Chemicals, TCI, Fisher Scientific, Carbosynth, Combi-Blocks, or Alfa Aesar, and used as received unless otherwise noted. Solvents (methanol (MeOH), acetone, acetonitrile (ACN), dichloromethane (DCM), dimethoxyethane (DME) and diethyl ether (Et2O), were used as received without further purification unless otherwise specified. Milli-Q water was used for all experiments. Deuterated solvents (CDCl 9 , and D 2 O) were obtained from Cambridge Isotope Laboratories and used as received. NMR
All NMR spectra were obtained on a Bruker Avance 400 or a Bruker DRX 500 MHz broad band FT NMR spectrometer. 1 HNMR and 13 C { 1 H} NMR spectra were referenced to residual protio- solvent signals, and both 1 'B and 11 B{ 1 H} chemical shifts were referenced to BF 3 *Et 2 O (15% in CDCl 3 , 5 0.0 ppm).
Synthesis of TBA 2 B 12 Cl 12 :
CS 2 B 12 H 12 (2.0 g, 5.0 mmol) and a dry stir bar were added to a clean, dry round bottom flask (250.0 mL). Under vigorous stirring, hydrochloric acid (3 M) was added dropwise using an addition funnel (60.0 mL). Excess sodium hypochlorite (40.0 mL, 6%) was slowly added to the round bottom via addition funnel (all joints were heavily greased and fitted with parafilm to trap any evolved gas) and the contents were stirred heavily. The sealed reaction was allowed to proceed at room temperature for 2 hrs. After, the round bottom was heated to 60 °C for 24 hrs. Unreacted chlorine was quenched with sodium sulfite until the reaction liquid was clear. Excess (2.2 equivalents per cluster) tetrabutvl ammonium bromide (TBA-Br) was dissolved in minimal water and added drop-wise to the reaction mixture. A white powder precipitated from solution and was collected via vacuum filtration. After 3 washes with water (10.0 mL), the product was collected and recrystallized from hot ethanol. Note: Conversion was monitored by 11 B NMR spectroscopy and ESI-MS(-). 11 B NMR (160 MHz, 25 °C, DMSO-d 6 ) 6: -10.4 ppm. ESI-MS(-) (MeCN) [M-+Na] : 577.7237 (calc’d, 577.7283) m/z. This species is observed as the [M'+Na] adduct under ESI-MS(-) conditions. Four multiplets are observed in the 1H NMR spectrum of TBA 2 B 12 Cl 12 , as consistent with the splitting pattern and integral ratio of the TBA cation. A singlet resonance consistent with perhalogenation of the cluster is observed in the 11 B NMR spectrum of TBA 2 B 12 Cl 12 . All resonances of the 13 C NMR spectrum of TBA 2 B 12 Cl 12 are consistent with the splitting pattern and integral ratio of the TBA cation.
Synthesis of TBA 2 B 12 Cl 9 (OH) 3 :
CS 2 B 12 H 12 (6.0 g, 15.0 mmol) and a dry stir bar were added to a clean, dry round bottom flask (300.0 mL) and the flask was placed into an ice bath. Under vigorous stirring, diluted sulfuric acid was added dropwise using an addition funnel (120.0 mL, 53% v/v). The round bottom flask was moved to an oil bath and fitted with a reflux condenser. The bath was heated to 110°C and the reaction was allowed to reflux for 20 hrs. After allowing the reaction to cool to room temperature after hydroxylation, the reflux condenser was removed and an addition funnel was fitted onto the round bottom flask. All joints were heavily greased and a stopper was placed on top of addition funnel to avoid any gas release. Additionally, parafilm was placed over all joints. Excess sodium hypochlorite (120.0 mL, 6%) was slowly added to the round bottom via addition funnel while the contents were stirred heavily. The reaction was allowed to proceed at room temperature for 2 hrs. After, the round bottom was heated to 60 °C for 24 hrs. Unreacted chlorine was quenched with sodium sulfite until the reaction liquid was clear. Excess (2.2 equivalents per cluster) tetrabutylammonium bromide (TBA-Br) was dissolved in minimal water and added drop-wise to the reaction mixture. A white powder precipitated from solution and was collected via vacuum filtration. After 3 washes with water (10.0 mL), the product was collected and recrystallized from hot ethanol. Note: Conversion was monitored by 11 B NMR spectroscopy and ESI-MS(-). 11 B NMR (128 MHz, 25 °C, CD 3 CN) 5: -7.2 ppm (s; B1,B7,B9), -13.5(s; B3,B4,B8,B6,B10,Bl l), -15.2(s;B2,B5,B12) . ESI-MS(-) (MeCN) [M- +H] : 499.8499 (calc’d, 499.8514) m/z. This species is observed as the [M-+H] adduct under ESI-MS(-) conditions. In the 1 HNMR spectrum of TBA 2 B 12 Cl 9 (OH) 3 , four multiplets are observed as consistent with the splitting pattern and integral ratio of the TBA cation. In addition, a singlet corresponding to the hydroxyl 1H atoms is observed. In the 11 B NMR spectrum of TBA 2 B 12 Cl 9 (OH) 3 , a resonance at -7.2 ppm ascribed to the B-0 bonds and overlapping resonances at -13.5 ppm and -15.2 ppm corresponding to the B-Cl bonds is observed. All resonances are consistent with the splitting pattern and integral ratio of the TBA cation in the 13 C NMR spectrum of TBA 2 B12Cl 9 (OH) 3 .
Synthesis of TBA 2 B 12 Cl 9 (OCH 3 ) 3 :
TBA 2 B12Cl 9 (OH) 3 (2.0 g, 2.0 mmol) and a dry stir bar were placed into a dry Schlenk flask (50.0 mL) and transferred into a nitrogen filled glovebox. Sodium hydride (NaH, 0.5 g, 20.0 mmol) and DME (10.0 mL) were added to the flask and it was sealed and transferred out of the glovebox. The flask was then removed from the glovebox and transferred to an oil bath. The oil bath was heated to 80 °C and methyl iodide (0.9 mL, 15.0 mmol) was slowly injected into the sealed flask under a flow of nitrogen. The reaction was allowed to proceed for 0.5 hrs. After, the reaction mixture w as quenched with MeOH so that all NaH had reacted. The DME and MeOH were removed under vacuum and the product was dissolved in DCM (10.0-15.0 mL) and passed through a silica plug. The filtrate was collected and dried under vacuum. 1 'B NMR (128 MHz, 25 °C, DMSO-d 6 ) 5: -9.8 ppm (s; Bl, B7, B9), -15.8 (s; B3,B4,B8,B6,B1O,B11), -17.6(s;B2,B5,B12). ESI-MS(-) (MeCN) [M-+H] : 541.8957 (calc’d, 541.8985) m/z. This species is observed as the [M'+H] adduct under ESI-MS(-) conditions. In the 1 HNMR spectrum of TBA 2 B 12 Cl 9 (OCH 3 ) 3 , four multiplets are observed as consistent with the splitting pattern and integral ratio of the TBA cation. In addition, a singlet at 3.48 observed and corresponds to the methoxy 1 H. The 11 B NMR spectrum of TBA 2 B 12 Cl 9 (OCH 3 ) 3 shows a resonance at -9.8 ppm ascribed to the B-0 bonds and overlapping resonances at -15.8 ppm and -17.6 ppm corresponding to the B-Cl bonds. The 13 C NMR spectrum of TBA 2 B 12 Cl 9 (OCH 3 ) 3 shows four resonances that correspond to the TBA cation and a fifth resonance ascribed to the methoxy 13 C.
Synthesis of C S2 B 12 B r 12 :
The procedure was adapted from Muetterties (Miller, H. C.; Muetterties, E. L.; Boone, J. L.;Garrett, P.; Hawthorne, M. F. Borane Anions. In Inorganic Syntheses; McGraw-Hill, Inc., 1967; pp 81-91). A solution of CS 2 B 12 H 12 (2.0 g, 5.0 mmol) in 50 mL of aqueous methanol (50% v/v) was cooled to 5 °C. Under vigorous stirring 5.0 mL (187.5 mmol) of B 12 were added dropwise. Once at room temperature the reaction was moved to an oil bath and fitted with a reflux condenser. An additional 5.0 mL of B r 2 were added and the reaction was allowed to reflux (90 °C) for 48 hrs. The solvent and unreacted B 12 were removed in vacuo. The white powder was recrystallized from water overnight. The recrystallized product was then introduced to 50 mL of aqueous methanol (50% v/v) in a clean round bottom flask (250.0 mL). 5.0 mL of B 12 were then added dropwise. The reaction was left under reflux (90 °C) for 24 hrs. The solvent and excess B 12 were removed in vacuo. The resulting white powder was recrystallized from w aler until full conversion was observed. Note: Conversion was monitored by 11 B NMR spectroscopy and ESI-MS(-) 1 HNMR and 13 C NMR are omitted as no resonances were anticipated for this sample. 11 B NMR (160 MHz, 25 °C, DMSO-d 6 ) 5: -12.96 ppm. ESI- MS(-) (MeCN) [M 2- ] : 544.0644 (calc’d, 544.0648) m/z. This species is observed as the [M 2- ] under ESI-MS(-) conditions.
Synthesis of TBA 2 B 12 Br 9 (OH) 3 :
CS 2 B 12 H 12 (2.0 g, 5.0 mmol) and a dry stir bar were added to a clean, dry round bottom flask (250.0 mL) and the flask was placed into an ice bath. Under vigorous stirring, diluted sulfuric acid was added dropwise using an addition funnel (120 mL, 53% v/v). The round bottom flask was moved to an oil bath and fitted with a reflux condenser. The bath was heated to 110°C and the reaction was allowed to reflux for 20 hrs. After allowing the reaction to cool, the reaction was diluted with MeOH (120.0 mL) and the vessel was charged with bromine (5.0 mL). The reaction was again fitted with a reflux condenser and heated to 80°C for 48 hrs. Excess (2.2 equivalents per cluster) tetrabutylammonium bromide (TBA-Br) was dissolved in minimal water and added drop-wise to the reaction mixture. The precipitate was isolated by vacuum filtration and washed with water (10.0 mL x 3). After, the product was dried in vacuo. 11 B NMR (128 MHz, 25 °C, CD 3 CN) 5: -7.5 ppm (s; B1,B7,B9), -16.8 (s; B3,B4,B8,B6,B1O,B11), -19.0 (s;B2,B5,B12). ESI-MS(-) (MeCN) [M-+Na] : 922.3774 (calc’d, 922.3749) m/z. This species is observed as the [M-+Na] adduct under ESI-MS(-) conditions. The 1 HNMR spectrum of TBA 2 B 12 Br 9 (OH) 3 shows four multiplets are observed as consistent with the splitting pattern and integral ratio of the TBA cation. The 11 B NMR spectrum of TBA 2 B 12 Br 9 (OH) 3 shows a resonance at -7.5 ppm ascribed to the B-0 bonds and overlapping resonances at -16.8 ppm and -19.0 ppm corresponding to the B-Cl bonds. The 13 C NMR spectrum of TBA 2 B 12 Br 9 (OH) 3 shows all resonances are consistent with the splitting pattern and integral ratio of the TBA cation.
Synthesis of TBA 2 B 12 Br 9 (OCH 3 ) 3 : TBA 2 B 12 Br 9 (OH) 3 (0.5 g, 0.35 mmol) and a dry stir bar were placed into a dry Schlenk flask (50.0 mL) and transferred into a nitrogen filled glovebox. Sodium hydride (NaH, 0.9 g, 3.5 mmol) and DME (10.0 mL) were added to the flask and it was sealed and transferred out of the glovebox. The flask was then removed from the glovebox and transferred to an oil bath. The oil bath was heated to 80 °C and methyl iodide (0.16 mL, 2.6 mmol) was slowly injected into the sealed flask under a flow of nitrogen. The reaction was allowed to proceed for 18 hrs. After, the reaction mixture was quenched with MeOH so that all NaH had reacted. The DME and MeOH were removed under vacuum and the product was dissolved in DCM (10.0-15.0 mL) and passed through a silica plug. The filtrate was collected and dried under vacuum. 11 B NMR (128 MHz, 25 °C, DMSO-d 6 ) 5: -7.4 ppm (s; B1,B7,B9),-16.4 (s; B3,B4,B8,B6,B1O,B11) , -19.0 (s;B2,B5,B12) . ESI-MS(-) (MeCN) [M-+Na] : 964.4276 (calc’d, 964.4220) m/z. This species is observed as the [M-+Na] adduct under ESI-MS(-) conditions. The 1 HNMR spectrum of TBA 2 B 12 Cl 9 (OCH 3 ) 3 shows four multiplets are observed as consistent with the splitting pattern and integral ratio of the TBA cation. In addition, a singlet at 3.5 ppm is observed and corresponds to the methoxy 1 H. The 11 B NMR spectrum of TBA 2 B 12 Br 9 (OCH 3 ) 3 with a resonance at -7.4 ppm ascribed to the B-O bonds and overlapping resonances at -16.4 ppm and -19.0 ppm corresponding to the B-Cl bonds. The 13 C NMR spectrum of TBA 2 B 12 Br 9 (OCH 3 ) shows four resonances that correspond to the TBA cation and a fifth resonance ascribed to the methoxy 13 C.
Cation Exchange Procedures
Cation exchange was achieved by adapting the procedure of Strauss and coworkers. Salts were dissolved in the following solvents and volumes: Table 1: Solvent mixtures utilized to solubilize all compounds for cation exchange.
Compound Acetonitrile (mL) Methanol (mL) Acetone (mL) TBA 2 B 12 Cl 12 5 5 TBA 2 B 12 Cl 9 (OH) 3 10 10 20
TBA 2 B 12 Cl 9 (OCH 3 ) 3 5 15 15
Cs 2 B 12 Br 12 10 15
TBA 2 B 12 Br 9 (OH) 3 5 5 TBA 2 B 12 Br 9 (OCH 3 ) 3 5 10 5
After dissolution, the Amberlyst-15 column (15 in) was prepared by passing 3 column volumes of the solvent mixture used to dissolve the given compound through the resin. After, the dissolved compound was loaded to the top of the column and allowed to elute (~l-2 drops/sec). Thesolvent was collected and dried in vacuo. An oily residue was collected, and deionized water (10 mL) was added. After, the pH was brought up to 7 using Li OH* H 2 O (200 mg/mL). Activated charcoal (1 g) was charged into the vessel and allowed to stir for 3-4 hrs. After, the activated charcoal was removed under vacuum filtration, washed with water (20 mL x 3) and the filtrate was collected. The filtrate was dried under vacuum and stored at 10 °C. 11 B NMR confirmed the presence of intact cluster, 7 Li NMR confirmed the presence of the alkali cation and 1 H NMR indicates loss TBA. All samples were prepared in D 2 O.
11 B NMR spectrum of Li 2 B 12 Cl 12 confirms no changes to the cluster occurred during cation exchange. 1 HNMR spectrum of Li 2 B 12 Cl 12 shows the only resonance observed can be attributed to residual water in D 2 O, suggesting all TBA cation had been exchanged. 7 Li NMR spectrum of Li 2 B 12 Cl 12 . The observed singlet confirms the presence of 7 Li in the sample.
11 B NMR spectrum of Li 2 B 12 Cl 9 (OH) 3 confirms no changes to the cluster occurred during cation exchange. 1 HNMR spectrum of Li 2 B 12 Cl 9 (OH) 3 shows the only resonance observed can be attributed to residual water in D 2 O, suggesting all TBA cation had been exchanged. 7 Li NMR spectrum of Li 2 B 12 Cl 9 (OH) 3 shows the observed singlet confirms the presence of 7 Li in the sample. 11 B NMR spectrum of Li 2 B 12 Cl 9 (OH) 3 confirms no changes to the cluster occurred during cation exchange. 1HNMR spectrum of Li 2 B 12 Cl 9 (OCH 3 ) 3 shows two resonances are observed and are attributed to residual water in D 2 O and methoxy 1 H indicating all TBA cation had been exchanged. 13 C NMR spectrum of Li 2 B 12 Cl 9 (OCH 3 ) 3 shows a singlet resonance is observed and is attributed to methoxy 13 C indicating all TBA cation had been exchanged. The 13 C NMR was referenced externally to 10% ethylbenzene in CDCl 3 . 7 Li NMR spectrum of Li 2 B 12 Cl 9 (OCH 3 ) 3 shows the observed singlet confirms the presence of 7 Li in the sample. 11 B NMR spectrum of Li 2 B 12 Br 12 confirms no changes to the cluster occurred during cation exchange. 7 Li NMR spectrum of Li 2 B 12 Br 12 shows the observed singlet confirms the presence of 7 Li in the sample. 1 1 B NMR spectrum of Li 2 B 12 Br 9 (OH) 3 confirms no changes to the cluster occurred during cation exchange. 1 HNMR spectrum of Li 2 B 12 Br 9 (OH) 3 , shows the only resonance observed can be attributed to residual water in D 2 O, suggesting all TBA cation had been exchanged. 7 Li NMR spectrum of Li 2 B 12 Br 9 (OH) 3 shows the observed singlet confirms the presence of 7 Li in the sample. 11 B NMR spectrum of Li 2 B 12 Br 9 (OCH 3 ) 3 confirms no changes to the cluster occurred during cation exchange. 1 HNMR spectrum of Li 2 B 12 Br 9 (OCH 3 ) 3 shows two resonances that may be attributed to residual water in D 2 O and methoxy ’H indicating all TBA cation had been exchanged. 13 C NMR spectrum of Li 2 B 12 Br 9 (OCH 3 ) 3 shows a singlet resonance is observed and is attributed to methoxy 13 C indicating all TBA cation had been exchanged. The 13 C NMR was referenced externally to 10% ethylbenzene in CDCh.
7 Li NMR spectrum of Li 2 B 12 Br 9 (OH) 3 shows the observed singlet confirms the presence of 7 Li in the sample.
Thermogravimetric Analysis
Thermogravimetric analyses were performed on a PerkinElmer Pyris Diamond TG/DTA under a constant flow of Argon (200 mL/min). Samples were heated in ceramic trays (5 mm) from 60 °C to 1000 °C at 10 °C/min. The following equation was used to assess the number of water molecules lost per lithium per sample:
Assessment of Solubility Li 2 B 12 Cl 12 , Li 2 B 12 Cl 9 (OH) 3 and Li 2 B 12 Cl 9 (OCH 3 ) 3 were added to a 96-well plate with enough compound to cover the bottom of the well The following solvents were added: (A) acetonitrile, (B) ethyl acetate, (C) methanol, (D) ethanol, (E) isopropanol , (F) hexanes and (G) chloroform. Table 2: Preliminary assessment of solubility for Li 2 B 12 Cl 12 , Li 2 B 12 Cl 9 (OH) 3 and Li 2 B 12 Cl 9 (OCH 3 ) 3 . P indicates partially soluble, S indicates soluble and I indicates insoluble.
Compound A B D E F G
Li 2 B 12 Cl 12 I P I I I I
Li 2 B 12 Cl 9 (OH) 3 I P I P P I
Li 2 B 12 Cl 9 (OCH 3 ) 3 P S P S S I
EXAMPLE 3
Synthesis:
TBA 2 B12Cl 9 (OH) 3 (1.0 g, 1.0 mmol) and a dry stir bar were placed into a dry Schlenk flask (50.0 rnL) and transferred into a nitrogen fdled glovebox. Sodium hydride (NaH, 0.25 g, 10.0 mmol) and DME (10.0 mL) were added to the flask and it was sealed and transferred out of the glovebox. The flask was then removed from the glovebox and transferred to an oil bath. The oil bath was heated to 70 °C and l-(2-Bromoethoxy)-2-(2-methoxyethoxy)ethane (Br- TEG) (7.5 mmol) was slowly injected into the sealed flask under a flow of nitrogen. The reaction was allowed to proceed for 18 hrs. After, the reaction mixture was quenched with MeOH so that all NaH had reacted. The DME and MeOH were removed under vacuum and the product was dissolved in DCM (10.0-15.0 rnL) and passed through a silica plug. The filtrate was collected and dried under vacuum. B 12 H 12 2- -
Scheme 3: Schematic detailing the generation of TBA 2 B 12 Cl 9 (OTEG) 3 .
Scheme 4: Schematic detailing the Li + cation exchange of TBA 2 B 12 Cl 9 (OTEG) 3 to form Li 2 B 12 Cl 9 (OTEG) 3 2- . Electrochemical characterization:
Figure 23 shows an overlay of cyclic voltammograms demonstrating the widening of the potential window in 0.1 V increments between 3.8 and 4.4 V to capture the redox couple for B 12 Cl 9 (OTEG) 3 . Cyclic voltammograms were collected using a scan rate of 100 mV/s and in IM LiTFSI in 50:50 in ethylene carbonate: dimethyl carbonate (EC:DMC). Lithium was used as a counter electrode and a reference electrode. Glassy carbon was used as a working electrode.
Figure 24 shows a cyclic voltammogram of B 12 Cl 9 (OTEG) 3 2- . The redox couple B12CI9- (OTEG) 3 2- is fully displayed when the potential is cycled between 3.0 V and 4.4V. The cyclic voltammogram was collected using a scan rate of 100 mV/s and in IM LiTFSI in 50:50 in ethylene carbonate: dimethyl carbonate (EC:DMC). Lithium was used as a counter electrode and a reference electrode. Glassy carbon was used as a working electrode.
EXAMPLE 4
Figure 22 shows a potential map of various weakly coordinating anion (WCA) clusters. The redox potentials (E1/2) for the 2- / 1- redox couple range from 2.89 V to 5.52 V vs Li/Li + based on the substitution at the boron centers (e.g., B-H, B-Cl, B-Br, B-OR, B-NO2), the degree of substitution (e.g, 0, 3, or 12 -OR substituents or 0, 9, or 12 halogen substituents), and the nature of the -OR group (R = -H, -Me, -OCH 2 C 6 F 5 , -OTEG, etc). The fully halogenated clusters have E1/2 potentials greater than 5.0 V vs Li/Li + . The fully substituted clusters of the type B12(OR)12 2- generally have E1/2 less than 4.0 V vs Li/Li + . The clusters with mixed halogen and -OR substitution of the type B 12 X x (OR) 12 -x 2- generally have E1/2 between 4.0 V and 5.0 V, vs Li/Li + . The potentials are given versus Li/Li + in IM lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in ethylene carbonate: dimethyl carbonate (EC:DMC) in a 50:50 ratio. Li was used as a counter electrode and reference electrode. Glassy carbon was used as a working electrode.
Figure 25 shows cyclic voltammograms of various WCA clusters showing their redox couples at high potentials. The CVs were collected by cycling between 2.0 V and 5.0 V vs Li/Li + at 100 mV/s scan speed with IM lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in ethylene carbonate: dimethyl carbonate (EC:DMC) in a 50:50 ratio. Li was used as a counter electrode and reference electrode. Glassy carbon was used as a working electrode.
Figure 26 shows an overlay of cyclic voltammograms of B 12 Cl 12 2- and B 12 Cl 9 (OH) 3 2- showing the redox couple of B 12 Cl 9 (OH) 3 2- at approximately 4.6 V vs Li/Li + . The CV was collected at 100 mV/s scan rate in IM LiTFSI in 50:50 EC:DMC. Li was used as counter and reference electrodes. Glassy carbon was used as a working electrode.
Figure 27 shows 11 B {H} and 11 B NMR spectra of TBA 2 B 12 Cl 9 (OH) 3 used in cyclic voltammetry experiments. The spectrum of B 12 H 9 (OH) 3 -2 is included for comparison with numbers showing the peak assignments. A D 2 O/H 2 SO 4 mixture was used as the solvent. EXAMPLE 5
There is an eminent market demand for safer, cheaper, higher capacity, and longer lifetime energy storage technologies and systems. One area of energy storage that has seen a resurgence in both academic and commercial interest over the past decade is solid-state electrolytes (SSEs) for all-solid-state batteries (ASSBs). Still, several technical challenges remain for ASSBs that limit their applications. Among these are the need to increase ionic conduction, broaden the electrochemical stability window, eliminate detrimental dendrite formation, and achieve high energy density. Closo-borates, specifically closo-M 2 B 12 H 12 (M= Li, Na), exhibit favorable properties relevant to SSEs, including ion selectivity, reduction stability, weak coordination to cations, and potential for device integration. Yet, their practical application as SSEs has stalled due to their inadequate ionic conductivity at room temperature. Although their open structures lead to rapid ionic conduction, this high conductivity is limited to the disordered, high- temperature polymorphs only accessible at temperatures over 300°C.
Synthetically designing boron clusters at the atomic level to modify lattice packing, can provide a pathway towards room temperature ionic conductivity. The weakly coordinating character of the robust anionic boron-cluster framework disclosed herein can be enhanced through the integration of halogens onto the vertices of the boron cage. Progress on this front includes developing a facile and scalable strategy for sequentially hydroxylating multiple vertices in the parent cluster. These compounds can be further polyhalogenated, resulting in a vertex-differentiated polyfunctionalized B 12-based scaffold. Additionally, a large-scale and versatile complete cation exchange method has been established for these perfunctionalized species, which circumvents the lengthy cation exchange procedures used previously. As such, one can access clusters containing H + , Li + , Na + and Cs + cations, which can modulate the resulting cluster packing lattice in the solid-state and solubility properties in solution. Disclosed herein are data addressing the structure/function relationship between vertex differentiation and the resulting electrochemical potential window upon cycling of these SSEs. Ionic conductivity in B 12-based boron clusters is generally achieved by thermally induced disorder in the structure, where the large, weakly coordinating anions rotate, creating a dynamic environment for the easy movement of cations. To compare the library of mixed halogenation/hydroxylation B 12-based Li + salts to established cluster-based WCAs, the ionic conductivity of the different clusters was determined by electrochemical impedance spectroscopy (EIS). Figure 28 shows the temperature dependence of the ionic conductivity in an Arrhenius plot. By analyzing the chemical nature of the anion on the conduction mechanism, it was determined that the total ionic conductivity is mediated only by Li + (cation) conduction — with no contribution from the core of the cage or any other functional groups. Li 2 B 12 (OH) 12 was used as a control, with a measured conductivity of 8.9 x 10 4 S cm" 1 at 300 °C. Also included in Figure 28 are data for Li 2 B 12 Cl 9 (OMe) 3 , Li 2 B 12 Br 12 , Li 2 B 12 Br«(OH) 3 , and Li 2 B 12 Br 9 (OMe) 3 . Li 2 B 12 Cl 12 has a conductivity of 4.0 x 10 4 S cm 4 at 300 °C, and Li 2 B 12 Cl 9 (OH) 3 has a conductivity of 7.6 x 10 4 S cm 4 at 300 °C. The high-temperature ionic conductivity of Li 2 B 12 Cl 9 (OH) 3 is similar to that of Li 2 B 12 (OH) 12 . The high ionic conductivity of Li 2 B 12 Cl 9 (OH) 3 at elevated temperatures suggests it is likely to have similar properties to Li 2 B 12 Cl 12 and L 12 B 12 (OH) 12 . In the Li 2 B 12 Cl 12 and Li 2 B 12 (OH) 12 perfunctionahzed analogues, the inert sphere undergoes a thermal polymorphic transition which facilitates anion reorientations, contributing to the cation diffusion and overall high ionic conductivity. Additionally, the low activation barriers in the energy interactions between cations and anions in a solid-state environment further facilitate ion diffusion and conductivity. This high ionic conductivity confirms the retention of WC A character in the solid state for these Li + salts. Due to their high ionic conductivity, these WCAs can act as solid-state electrolytes. In one example, the WCAs disclosed herein can be included as solid-state electrolytes in an electrochemical cell that includes an anode and a cathode. In another example, the WCAs disclosed herein can be included as liquid-state electrolytes in a three-electrode electrochemical cell that includes a working electrode, a counter electrode, and a reference electrode.
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