LEE, Darren Frank (3 Chilterns Close, The Country ParkWest Derby,Liverpool, Merseyside L12 0NT, GB)
BLAGG, Robin Joseph (Apt 3, Eden Court42 Wilbraham Road,Fallowfield, Manchester M14 7SD, GB)
CLOKE, Frederick Geoffrey Nethersole (72 Stanford Avenue, Brighton, Sussex BN1 6FD, GB)
LEE, Darren Frank (3 Chilterns Close, The Country ParkWest Derby,Liverpool, Merseyside L12 0NT, GB)
BLAGG, Robin Joseph (Apt 3, Eden Court42 Wilbraham Road,Fallowfield, Manchester M14 7SD, GB)
| CLAIMS 1. A method for the treatment of mixtures of gases, said method comprising contacting said gaseous mixtures with trivalent metal complexes, wherein the components of said gaseous mixtures become bound to said metal complexes in synthetically useful gas-metal complexes. 2. A method for the preparation of synthetically useful gas-metal complexes, said method comprising the treatment of mixtures of gases by contacting said gaseous mixtures with trivalent metal complexes, wherein the components of said gaseous mixtures become bound to said metal complexes in said gas-metal complexes. 3. A method as claimed in claim 1 or 2 wherein said trivalent metal complexes comprise complexes of actinide metals. 4. A method as claimed in claim 3 wherein said complexes of actinide metals comprise complexes of uranium. 5. A method as claimed in claim 1 or 2 wherein said trivalent metal complexes comprise complexes of transition metals. 6. A method as claimed in claim 5 wherein said complexes of transition metals comprise complexes of titanium, zirconium or hafnium. 7. A method as claimed in any one of claims 1 to 6 wherein said trivalent metal complexes comprise sandwich complexes. 8. A method as claimed in claim 7 wherein said sandwich complexes comprise sandwich complexes of uranium which comprise two ring systems which are selected from substituted or unsubstituted aromatic and heterocyclic ring systems. 9. A method as claimed in claim 8 wherein said aromatic ring systems comprise Cs to C10 aromatic rings. 10. A method as claimed in claim 9 wherein said C5 to Ci0 aromatic rings are selected from pentalenyl, indenyl, fluorenyl, cydopentadienyl and cyclooctatetraenyl rings. 1 1. A method as claimed in claim 8 wherein said heterocyclic ring system is selected from nitrogen-containing heterocycles. 12. A method as claimed in any one of claims 8 to 1 1 wherein said ring systems are substituted with from 1 to 5 ring substituents. 13. A method as claimed in claim 12 wherein said ring substituent groups comprise groups selected from alkyl, silyl and alkylsilyl groups. 14. A method as claimed in claim 13 wherein said groups are selected from methyl groups, butyl groups, trimethylsilyl groups and triisopropyfsilyl groups. 15. A method as claimed in claim 14 wherein said trivalent metal complexes comprise uranium(lll) mixed sandwich complexes of the general formula [U(L'){L")(thf)„], where L' is a mono-anionic six-electron donor such as substituted cydopentadienyl, substituted indenyl or a tri-dentate hydrotris(pyrazolyl)borate, L" is a di-anionic ten-electron donor, such as cyclooctatetraene or pentalene with two tri-/so-propylsilyl substituents, thf indicates that certain complexes were obtained as thf adducts, and n is 0 or an integer. 16. A method as claimed in claim 15 wherein said trivalent metal complexes comprise 1 ,4-di(trialkylsilyl)cyciooctatetraene/methylated cydopentadienyl mixed sandwich uranium(lll) complexes (1), ^-diitrialkylsilyljpentalene/methylated cydopentadienyl mixed sandwich uranium(lll) complexes (2), and 1 ,4-di(trialkylsilyl)cyclooctatetraene/ methyl(silyl)ated indenyl mixed sandwich uranium(lll) complexes (3): (1 ) (2) (3) R= SiMe3, SMPr3 R= SiMe3, Si'Pr3 R"= Me (1-3), 'Bu (1-2), S!Me3 (1 -2), V( (1 -2) R'= Me (1-5), 'Bu (1 -3), SiMe3 (1-3) R"= Me (0-4) GENERAL EXAMPLES In (1 ) and (2): R = -CH3 or -CH(CH3)2; R' = -CH3, -C(CH3)3 or Si(CH3)3; when R' n = 1-5, and when R' = -C(CH3)3 or Si{CH3)3, n = 1-3. In (3): R = -CH3 or -CH(CH3)2; R" = -CH3, -CH(CH3)2, -C(CH3)3 or Si(CH3)3; when R' = -CH3, p = 1 -3, and when R' = -CH(CH3)2, -C(CH3)3 or Si(CH3)3, p = 1-2; R" = CH3; r = 0-4. 7. A method as claimed in claim 16 wherein said trivalent metal complexes comprise the 1 ,4-di(triisopropylsilyl)cydooctatetraene/pentamethylcyclopentadienyl mixed sandwich uranium(lll) complex (4), the 1 ,4-di(triisopropylsilyl)cyclooctatetraene/ tetramethy!cyclopentadienyl mixed sandwich uranium(lll) complex (5), or the 1 ,4- di(triisopropylsilyl)cyclooctatetraene/hexamethylindenyl mixed sandwich uranium(lll) complex (6): (4) (5) (6) PREFERRED EXAMPLES 18. A method as claimed in any preceding claim wherein the gaseous molecules comprised in said mixtures of gases comprise polar gaseous molecules. 19. A method as claimed in claim 18 wherein said polar gaseous molecules are comprised of the oxides of carbon, nitrogen and sulphur. 20. A method as claimed in claim 18 or 19 wherein said mixtures of gases comprise at least one of carbon monoxide, carbon dioxide, nitrogen monoxide, nitrogen dioxide, dinitrogen monoxide and sulphur dioxide. 21. A method as claimed in claim 18, 19 or 20 wherein said gaseous mixtures additionally comprise at least one additional gas. 22. A method as claimed in claim 21 wherein said at least one additional gas is selected from ammonia, hydrogen sulphide, carbon disulphide, hydrogen, substituted or unsubstituted hydrocarbons and haiocarbons. 23. A method as claimed in claim 22 wherein said unsubstituted hydrocarbon is methane. 24. A method as claimed in any preceding claim wherein the gaseous molecules comprised in said mixtures of gases are radioactively labelled. 25. A method as claimed in claim 24 wherein said radioactively labelled gaseous molecules are the oxides of carbon which are 1 C or 13C labelled. 26. A method as claimed in any preceding claim wherein said gaseous mixtures are contacted with said trivalent metal complexes at ambient temperature and pressure. 27. A synthetically useful gas-metal complex, said gas-metal complex comprising the complex formed by the treatment of mixtures of gases with trivalent metal complexes, wherein the components of said gaseous mixtures become bound to said metal complexes in said gas-metal complexes. 28. A gas-metal complex as claimed in claim 27 which comprises a complex obtained from the reaction of mixtures of gases comprising at least one oxide of carbon and at least one other gas selected from at least one of hydrogen, ammonia or an oxide of nitrogen with trivalent metal sandwich complexes of uranium which comprise two aromatic ring systems selected from pentalenyl, indenyl, fluorenyl, cyclopentadienyl and cyclooctatetraenyl rings. 29. A method for the production of organic chemical compounds, said method comprising the treatment of the gas-metal complexes as claimed in claims 27 and 28. 30. A method as claimed in claim 29 wherein said treatment comprises electrochemical treatment of said gas-metal complex. 31. A method as claimed in claim 30 wherein said electrochemical treatment of said gas-metal complexes comprises bulk electrochemical techniques involving controlled potential electrolysis. 32. A method as claimed in claim 31 wherein electrochemically reduction of samples of di-uranium(IV) deltate and squarate complexes is achieved by applying a reductive potential between gold and platinum mesh electrodes through a [nBu4N][B{C6F5)4]/tetrahydrofuran solution containing the said complexes. 33. A method as claimed in claim 32 wherein said reduction potential is approximately 0.25 V more negative than the reduction potential of the said complexes. 34. A method for the preparation of organic chemical compounds, said method comprising: (a) treating mixtures of gases by contacting said gaseous mixtures with trivalent metal complexes, wherein the components of said gaseous mixtures become bound to said metal complexes in said gas-metal complexes; and (b) treating said gas-metal complexes in an electrochemical cell. |
[0001] The present invention relates to metal complex compounds and their reactions with small gaseous molecules. More specifically it is concerned with the use of uranium complexes in the treatment of gases such as the oxides of carbon, nitrogen and sulphur and the synthetically valuable compounds thereby obtained.
Background to the Invention
[0002] The detrimental environmental impact associated with the generation of so-called "greenhouse gases", and the role of these gases in the phenomenon of global warming, are well known and much attention has been devoted to the development of different means by which the volumes of such gases released in emissions may be reduced. Thus, for example, the production of large volumes of greenhouse gases by electricity generation associated with the burning of fossil fuels has resulted in greater interest in alternative means of generation, such as wind, wave and solar power, as well as nuclear power generation. Also, greenhouse gas emission associated with various modes of transport - and most particularly with the rapid growth in use of the internal combustion engine and in the use of air transport - has resulted in significant efforts being made in various quarters to reduce the frequency and distance of journeys.
[0003] However, despite the efforts being made to reduce the volumes of greenhouse gases which are emitted into the atmosphere, their presence will continue to cause problems for many years to come, since it would be impossible to change with sufficient rapidity systems and devices which are already well established commercially. Consequently, attention has turned to alternative approaches, wherein the greenhouse gases which are emitted are subsequently treated so as to reduce or eliminate the volumes which are released into the atmosphere.
[0004] One approach to this problem which has been adopted in certain situations is the use of scrubbers, which are designed to remove the greenhouse gases from the gaseous effluent by reaction or dissolution in a liquid - typically aqueous - scrubbing medium. The disadvantage with this approach, however, is that whilst volumes of gaseous effluents may be significantly reduced in this way, different problems are created as the result of the generation of significant volumes of liquid effluents.
[0005] An alternative means of addressing the problem may involve the use of adsorbents, such as activated charcoal, over which the gases are allowed to pass, the specific adsorbent being chosen so as to preferentially adsorb the greenhouse gases which are of particular concern from an environmental perspective in a given situation. However, the large volumes of gases which often have to be treated would typically require the use of significant amounts of adsorbent, with the attendant problems of cost and disposal of adsorbent.
[0006] A more successful approach, however, considers the use of materials which are capable of chemical reaction with - rather than simple physical adsorption of - these greenhouse gases, since this offers the potential for the generation of chemical compounds which might prove to be useful in their own right, and this has been the basis of the investigations conducted by the present inventors, Thus, whilst many previous efforts via this route have utilised very aggressive, hazardous and expensive techniques - so that, for example, the removal of carbon monoxide has typically been achieved via methods including reductive cyclomerisation using media such as alkali metals in liquid ammonia, or by means of electrolysis procedures - the present inventors have found that a more convenient and less hazardous approach to the problem has allowed for a range of potentially synthetically useful intermediates to be obtained.
[0007] The approach adopted has utilised specific metal complex compounds. Compounds of this type have previously been disclosed in the prior art. Thus, for example, there are described in WO-A-99/09034 complexes of trivalent metals, principally thorium and uranium, which find particular use as nitrogen fixation agents, for the production of precursors for ammonia production, and for inserting nitrogen into compounds during synthesis reactions. The disclosed complexes incorporate dinitrogen in their structure and illustrate the capture of a small molecule in a larger metal complex molecule. However, the disclosed complexes are exclusively based on the formation of structures incorporating an inert, symmetrical structure, in the form of nitrogen.
[0008] Compounds incorporating uranium which could be used in the preparation of the complexes disclosed in WO-A-9909034 were previously known from WO-98/20971 , wherein there were disclosed compounds, and particularly catalysts, which comprised complexes of actinides with at least one ligand, the disclosed compounds being described as finding particular use in the catalysis of polymerisation reactions. This document contained no suggestion of the use of the said compounds in the preparation of complexes by the incorporation of small molecules.
[0009] In an earlier patent application WO-A-2009/007755, the present inventors sought to develop an approach by means of which complexes may be formed by the chemical interaction of compounds with small molecules, specifically the small gaseous molecules which comprise greenhouse gases, thereby allowing these gases to be removed from the atmosphere, and reported that some polar molecules of greenhouse gases were found to be capable of complex formation with certain complexes of actinide and other metals. Thus, it was reported that certain trivalent metai sandwich complexes reacted with carbon monoxide at atmospheric pressure at temperatures anywhere between -78° and 25°C in an inert solvent such as diethyl ether or toluene to form squarate or deltate derivatives, and similar results were achieved by the reaction of the complexes with carbon dioxide.
[0010] Thus, there was provided an efficient and convenient means for the removal of certain gases from the atmosphere through their reaction with the metal complexes, and the disclosed method appeared to be useful for the removal of so-called greenhouse gases from the atmosphere, thereby offering potential environmental benefits.
[0011] The present inventors have, however, now further developed this approach to the treatment of greenhouse gases and have also sought to address a further major problem associated with the rapid depletion of the world's resources. Specifically, the dwindling natural reserves of chemical feedstocks, most particularly associated with the reduction in oil reserves presents major potential problems for the chemical manufacturing industry in coming years, and the development of alternative resources is likely to become a major priority.
[0012] Thus, by adapting the approach of binding gaseous molecules by contacting gases comprising these molecules with metal complexes, the present inventors have developed a system which not only allows for the removal of hazardous gases from the atmosphere, but also facilitates the production of a range of synthetically useful products. The approach is based on the recognition that by treating selected mixtures of gases, most specifically, gases which present an environmental hazard, it is possible to generate a range of chemical products containing different chemical structures which may subsequently be used as intermediates for the production of a wide variety of useful end- products. As a particular example, the treatment of gaseous mixtures containing oxides of carbon and nitrogen-containing gases affords the possibility for the production of many synthetically useful nitrogen-containing organic compounds. Summary of the Invention
[0013] Thus, according to a first aspect of the present invention, there is provided a method for the treatment of mixtures of gases, said method comprising contacting said gaseous mixtures with trivalent metal complexes, wherein the components of said gaseous mixtures become bound to said metal complexes in synthetically useful gas-metal complexes. [0014] According to a second aspect of the present invention, there is provided a method for the preparation of synthetically useful gas-metal complexes, said method comprising the treatment of mixtures of gases by contacting said gaseous mixtures with trivalent metal complexes, wherein the components of said gaseous mixtures become bound to said metal complexes in said gas-metal complexes,
[0015] Gaseous molecules comprised in said mixtures of gases typically may comprise polar gaseous molecules, including molecules of greenhouse gases, such as the oxides of carbon, nitrogen and sulphur. Most particularly, said gases comprise carbon monoxide, carbon dioxide, nitrogen monoxide, nitrogen dioxide, dinitrogen monoxide and sulphur dioxide, but the use of the method of the invention also envisages reactions involving gas mixtures which comprise gaseous molecules such as ammonia, hydrogen sulphide and carbon disulphide, as well as hydrogen, hydrocarbons, which may be substituted or unsubstituted (such as methane), and halocarbon derivatives, The procedure of the invention results in the reductive combination of the target gaseous molecules such that, in the case of the oxides of carbon, for example, higher oxygenated hydrocarbons are produced.
[0016] Optionally, the gaseous molecules may be radioactively labelled. Preferred examples of radioactively labelled gaseous molecules include the oxides of carbon which are 11 C or 13 C labelled.
[0017] The processes of the invention may be carried out at sub-ambient temperatures and atmospheric pressure and, as such, offer significant advantages over the methods of the prior art.
[0018] In particularly preferred examples of the invention, said mixtures of gases comprise mixtures of at least one oxide of carbon with at least one other gas. More preferably, said at least one other gas comprises hydrogen or a nitrogenous gas, such as ammonia or an oxide of nitrogen. Especially preferred examples of gas mixtures include mixtures of carbon monoxide and/or carbon dioxide with at least one of hydrogen, nitrogen monoxide or ammonia.
[0019] Trivalent metal complexes which are particularly useful in the context of the present invention include complexes of transition metals, such as titanium, zirconium or hafnium. More preferably, however, said trivalent metal complexes comprise complexes of actinide metals, particularly suitable examples of which include complexes of uranium, Most preferably, said complexes comprise sandwich complexes and, most particularly, said complexes comprise sandwich complexes of uranium which comprise two ring systems which are selected from aromatic and heterocyclic ring systems. [0020] Typically, said aromatic ring systems comprise C 5 to C 10 aromatic rings including, for example, pentalenyi, indenyl, fluorenyl, cyclopentadienyl and cyclooctatetraenyl rings Especially preferred are the Cs to C 8 aromatic ring systems. Particularly suitable examples of the trivalent metal complexes comprise two ligands selected from indenyl, cyclopentadienyl and cyclooctatetraenyl ligands.
[0021] Suitable heterocyclic ring systems include nitrogen-containing heterocycles, such as pyrazoles.
[0022] Optionally, said ligands may be unsubstituted or, alternatively, they may be substituted with from 1 to 5 ring substituents. Typically said ring substituent groups comprise groups selected from alkyl, silyl and alkylsilyl groups, with Ci -5 alkyl and alkylsilyl groups being most preferred. Particularly preferred in this respect are methyl groups, butyl groups, preferably tertiary butyl groups, methylsilyl groups and propylsilyl groups, most particularly isopropylsilyl groups. The preferred substituents may comprise mono-, di-, or trialkylsilyl groups, and the most preferred groups are trimethylsilyl and triisopropylsilyl groups.
[0023] Preferred examples of trivalent metal complexes employed by the inventors for the purposes of the present invention have included various uranium(lll) mixed sandwich complexes of the general form [U(L')(L")(thf) n ], where U is a mono-anionic six-electron donor such as substituted cyclopentadienyl, substituted indenyl or a tri-dentate hydrotris(pyrazolyl)borate, L" is a di-anionic ten-electron donor, preferably either cyclooctatetraene or pentalene, with two tri-/so-propylsilyl substituents, thf indicates that certain complexes were obtained as thf adducts, and n is 0 or an integer.
[0024] According to a third aspect of the invention, there is provided a synthetically useful gas-metal complex, said gas-metal complex comprising the complex formed by the treatment of mixtures of gases with trivalent metal complexes, wherein the components of said gaseous mixtures become bound to said metal complexes in said gas-metal complexes.
[0025] Most preferably, said gas-metal complexes comprise complexes obtained from the reaction of mixtures of gases comprising at least one oxide of carbon and at least one other gas selected from at least one of hydrogen, ammonia or an oxide of nitrogen with trtvaient metal sandwich complexes of transition metals, such as titanium, zirconium or hafnium, or of actinide metals, most particularly uranium, which comprise two aromatic ring systems, preferably selected from pentalenyi, indenyl, fluorenyl, cyclopentadienyl and cyclooctatetraenyl rings. [0026] The present inventors also envisage the treatment of said gas-metal complexes in order to obtain a series of organic chemical intermediates. This, according to a fourth aspect of the invention, there is provided a method for the production of organic chemical compounds, said method comprising the treatment of the gas-metal complexes of the third aspect of the invention, Most preferably, said treatment comprises electrochemical treatment of said gas-metal complex.
[0027] Thus, the invention envisages a method for the preparation of organic chemical compounds, said method comprising:
(a) treating mixtures of gases by contacting said gaseous mixtures with trivaient metal complexes, wherein the components of said gaseous mixtures become bound to said metal complexes in said gas-metal complexes; and
(b) treating said gas-metal complexes in an electrochemical cell. Description of the Invention
[0028] The present invention provides for the treatment of gaseous mixtures with trivaient metal complexes, thereby facilitating the bonding of gases which include greenhouse gases to the metal complexes to form gas-metal complex compounds, wherein these gas-metal complexes provide a source of chemica! intermediates which have potential application in the production of a variety of products including, for example, pharmaceuticals, agrochemicais, cosmetics, dyestuffs and fine chemicals.
[0029] Preferred examples of trivaient metal complexes of use for the performance of the invention include 1 ,4-di(trialkyisilyl)cyclooctatetraene/methylated cyclopentadienyl mixed sandwich uranium{l!l) complexes (1 ), 1 ,4-di(trialkylsilyl)pentalene/methylated cyclopentadienyl mixed sandwich uranium(lll) complexes (2), and 1 ,4- di(trialkylsilyl)cyclooctatetraene/methyl(silyl)ated indenyl mixed sandwich uranium(lll) complexes (3), as illustrated below: (1 ) (2) (3)
R= SiMe 3 , Si'Pr 3
R= SiMe 3 , Si'Pr 3 R'= Me (1 -3), 'Bu (1-2), SiMe 3 (1-2), 'Pr (1 -2)
R'= Me (1 -5), 'Bu (1-3), SiMe 3 (1-3) R"= Ms (0-4)
GENERAL EXAMPLES
In (1) and (2): R = -CH 3 or -CH(CH 3 ) 2 ; R' = -CH 3 , -C(CH 3 ) 3 or Si(CH 3 ) 3 ; when R' = -CH 3 , n = 1-5, and when R' = -C(CH 3 ) 3 or Si(CH 3 ) 3 , n = 1-3.
In (3): R = -CH 3 or -CH(CH 3 ) 2 ; R' = -CH 3 , -CH(CH 3 ) 2 , -C(CH 3 ) 3 or Si(CH 3 ) 3 ; when R * = -CH 3 , p = 1-3, and when R 1 = -CH(CH 3 ) 2 , -C(CH 3 ) 3 or Si(CH 3 ) 3 , p = 1 -2; R" = CH 3 ; r = 0-4.
[0030] A particularly preferred complex comprises a 1 ,4-di(triisopropylsilyl) cyclooctatetraene/methylated cyclopentadienyl mixed sandwich uranium(lll) complex, most preferably a 1 ,4-di(triisopropylsilyl)cyclooctatetraene/pentamethyl-, tetramethyl- or trimethyl-cyclopentadienyl mixed sandwich uranium(lll) complex.
[0031] Said complexes are typically prepared from the metals via the corresponding metal halides, the method of preparation comprising:
(a) reacting the metal with a halide salt;
(b) reacting the resulting metal halide with a first metal aromatic compound; and
(c) reacting the intermediate so formed with a second metal aromatic compound.
[0032] Particularly suitable halide salts for use in the first stage of the synthesis are mercury(ll) halides, most particularly mercury(ll) iodide. The reactions are typically carried out at elevated temperatures over a prolonged period of time in a sealed tube.
[0033] The metal aromatic compounds used in the formation of the complex are preferably alkali metal aromatic compounds, most particularly potassium aromatic compounds such as pentamethyl-, tetramethyl- or trimethyl-cyclopentadienyl potassium and 1 ,4-di(triisopropylsilyl) cyclooctatetraenyl dipotassium. Reactions of these compounds with the metal haiide are typically carried out in organic solvents such as tetrahydrofuran at room temperature and pressure.
[0034] The preferred 1 ,4-di(triisopropylsilyl)cyclooctatetraene/pentamethyl-, tetramethyl- or trimethyi-cyclopentadienyl mixed sandwich uranium(lll) complexes may be prepared from uranium turnings by firstly reacting the uranium with mercury(ll) iodide at 320°C for 2 days in a sealed tube, and then reacting the resulting uranium(lll) iodide firstly with pentamethyl-, tetramethyl- or trimethyl-cyclopentadienyl potassium, and then with 1 ,4- dt(triisopropylsilyl)cyclooctatetraenyl dipotassium, both reactions being carried out at room temperature and pressure in tetrahydrofuran.
[0035] In further preferred embodiments of the invention, useful trivalent metal complexes include 1 ,4-di(triisopropylsi!yl)cyclooctatetraene/cyclopentadienyl mixed sandwich uranium(IN) complexes wherein the cyclopentadiene ring is substituted with alkyl groups other than methyl groups. Preferred alkyl groups include butyl groups, most preferably t-butyl groups. In other preferred embodiments, the substituents comprise mono-, di~, or trialkylsilyl groups, and the most preferred groups in this context are trimethylsily! groups. Some or all of the ring carbon atoms of the cyclopentadiene ring may be substituted with the aforementioned groups but, preferably, the ring carries 3, 4 or 5 substituents, and these substituents may be the same or different.
[0036] Specific examples of preferred compounds in this context include the 1 ,4- di(triisopropylsilyl)cyclooctatetraene/pentamethylcyclopenta dlenyl mixed sandwich uranium(lll) complex (4), the 1 ,4-di(triisopropylsilyl)cyclooctatetraene/tetramethyl cyclopentadienyl mixed sandwich uranium(lll) complex (5), and the 1 ,4-di(triisopropylsilyl) cyclooctatetraene/hexamethylindenyl mixed sandwich uranium(lll) complex (6):
PREFERRED EXAMPLES [0037] Initially, the present inventors established that such trivalent metal complexes react with carbon monoxide at atmospheric pressure at temperatures anywhere between -78° and 25°C in an inert solvent such as diethyl ether or toluene to form squarate or deltate derivatives. Similar results were successfully achieved by the reaction of the complexes with carbon dioxide.
[0038] Thus, it was shown that [U(Cp R )(C 8 H 6 (Si'Pr 3 ) 2 )] (Cp R = Cp Me5 , Cp Me4 ) reacted with or, more specifically, 'reductively coupled' carbon monoxide under mild conditions, as shown in Scheme 1.
Scheme 1 Reaction of uranium(lll) mixed-sandwich complexes with carbon monoxide to generate di-uranium(IV) oxocarbon complexes
[0039] The reactions between excess carbon monoxide and [U(Cp R )(C 8 H s (Si'Pr 3 )2)] result in generation of di-uranium(IV) complexes with the bridging oxocarbon (CO)„ 2 ~ fragments, detlate C 3 0 3 2~ and squarate C 4 0 4 2- . These members of the oxocarbon series, which are shown in Figure 1 , have previously been synthesised, but under energy intensive conditions requiring the use of high temperatures and pressures. According to the procedures adopted by the present inventors, however, their generation using uranium(lll) mixed-sandwich complexes occurs at sub-ambient temperatures and pressures.
deltate squarate croconate rhodlzonate
Figure 1 The oxocarbon series [0040] it has previously been demonstrated that the squarate fragment can be liberated from [{U(Cp Me4 )(C 8 H4(Si i Pr3) 2 )}2(C 4 0 4 )] as C,0,(Me 3 Si) 2 by reacting the di-uranium(IV) complex with two equivalents of e 3 SiCI, thereby also resulting in the generation of uranium(IV) chloride, as illustrated in Scheme 2.
Scheme 2 Liberation of squarate with e 3 SiCf
[0041] Thereafter, regeneration of the reactive uranium(ill) precursor from the uranium(IV) chloride would allow the cycle of squarate generation and liberation to be closed, and this reduction/chloride abstraction process could be performed using chemical and/or electrochemical techniques.
[0042] The proposed mechanism of deltate/squarate formation is illustrated in Scheme 3:
Scheme 3 Reaction of uranium(lll) mixed sandwich complexes with one equivalent of carbon monoxide, via reactive intermediates [0043] Thus, following initial coordination of carbon monoxide, two uranium carbonyl complexes dimerise which, together with C-C bond formation, gives a 'zig-zag' bridging ethyne diolate. This complex has a significant lifetime, but will eventually rearrange to give an unreactive linear ethyne diolate. The 'zig-zag' intermediate however will react further with CO gas, leading to the delta te/squarate complexes. If this species is also reactive with other small molecules, e.g. H 2 (g), NO(g), C0 2 (g), C x H y (g), then it is clear that there is potential for a wide range of potentially novel fragments to be generated.
[0044] The replacement of carbon monoxide with carbon dioxide in reactions with [U(Cp R )(C 8 H6(Si' ' Pr 3 )2)] (Cp R = Cp MeS , Cp Me ") results in the generation of di-uranium(!V) complexes with a bridging carbonate group, together with the liberation of carbon monoxide, as shown in Scheme 4.
= H, Ms
Scheme 4 Reaction of uranium(ll l) mixed-sandwich complexes with carbon dioxide to generate di-uranium(IV) carbonate complexes
[0045] The liberated CO gas can then go on and react with the uranium(lll) starting material to give the deltate/squarate complexes. Thus, the reaction of [U(Cp e4 )(C 8 He(Si' ' Pr 3 )2)] with 0.8 equivalents of C0 2 gas results in generation of di- uranium(IV) carbonate and squarate complexes in a 4: 1 ratio.
[0046] Specific examples of triva!ent metal complexes employed by the inventors for the purposes of the present invention have included various uranium(ll l) mixed sandwich complexes of the general form [U(L')(L")(thf) n ], where L' is a mono-anionic six-electron donor such as substituted cyclopentadienyl, substituted indenyl or a tri-dentate hydrotris(pyrazolyi)borate, as shown in Figure 2 and L" Is a di-anlonic ten-electron donor, either cyclooctatetraene or pentalene, with two trl-/so-propylsilyl substituents, as illustrated in Figure 3. "thf" indicates that certain complexes were obtained as thf adducts <n is 0 or an integer).
R = H, Me R = H, Me
Figure 2 L' Itgands used in uranium(l il) mixed sandwich complexes:
(a) cyciopentadienyl, Cp R ; (b) indenyl, lnd R ; (c) hydrotris(pyrazolyi)borate, Tp R
Figure 3 L" ligands used in uranium(lll) mixed sandwich complexes: (a) 1 ,4- triisopropyisilyl-cyclooctatetraene; (b) 1 ,4-triisopropylsilyl-pentalene
[0047] The complexes which have been successfully synthesised, isolated and characterised (by NMR spectroscopy, mass spectrometry, elemental analysis and in some cases X-ray crystallography) include the foilowing:
[U(Cp e5 )(C 8 He(Si'Pr 3 ) 2 )(thf)]; [U<Cp e4 )(C 8 H 6 (Si f Pr 3 ) 2 )(thf)]; [U(\nd Me7 )(C 6 e(S\'Pr a ) 2 )l [U(!nd Me6 )(C 8 H 6 (Si'Pr 3 ) 2 )]; [U(Tp Me2 )(C B H s (Si'Pr 3 ) 2 )]; [U(Cp Me5 )(C e H 4 (Si'Pr 3 ) 2 )]; and [U(Tp e2 )(C 8 H 4 (Si'Pr 3 ) 2 )].
[0048] Whilst some of these complexes are obtained as thf adducts, the thf can be (and preferably is) easily removed prior to further reactions, by heating to +1 1 OX under a vacuum of 10 ~5 mbar since, although the presence of bound thf does not prevent further reaction, it can affect rates of reaction, in addition to adding another variable to the system, of which account must be taken.
[0049] These uranium(l!l) mixed-sandwich complexes have been reacted with various single- and mixed-gas systems, with measurement and addition of the gases performed using a calibrated high vacuum line attached to a mercury piston (Toepler pump). The use of isotopically labelled gases, specifically 13 C-labelled CO (g) and C0 2( g } , allowed for the observation of any product species via NMR spectroscopy, although conclusive identification of species relied on the use of X-ray crystallography.
[0050] The extent of the reactivity of various trivalent metal complexes with carbon monoxide is set out in Table 1 . Complex 5 C / ppm Characterised by X-ray
crystallography
[U(Cp Me5 )(C B H s (Si'Pr 3 ) 2 )] † +225.0
[U(Cp Me4 )(C 8 H s (Si' ' Pr 3 )2)] -11 1.4
[U(lnd Me7 )(C e H 6 (Si'Pr 3 ) 2 )] +359 -
[U(lnd e8 )(C s H e (Si'Pr 3 ) 2 )] +270, -58
[U(Tp Me2 )(C 8 H 4 <Si'Pr 3 ) 2 )] +235,5, +204.7 -
T Upon reaction with one equivalent CO(g), a single product with 5 C +313 ppm,
[{U(Cp Me5 )(C a H e (Si'Pr 3 ) 2 )}(C 2 0 2 )], is observed
Table 1 Reactivity of uranium(lll) mixed sandwich complexes with excess carbon monoxide
[0051] Thus, in the case of [U(lnd Me6 )(C 8 He(Si'Pr 3 )2)j, the addition of excess CO gas led to the isolation of a di-uranium(IV) squarate complex, analogous to that obtained from as shown in Scheme 5.
Scheme 5 Reaction of [U(lnd Mee ){CaH6(Si'Pr 3 )2}] with carbon monoxide
[0052] The reactivity of these trivaient mstal complexes with carbon dioxide may be gleaned from Table 2. Complex 5 C / ppm Characterised by X-ray
crystallography
[U(Cp Me5 )(C 3 H 6 (Si'Pr 3 ) 2 )] +113.2 -
[U(Cp Me4 )(C 8 H e (Si' ' Pr 3 ) 2 )] +137,6
[U(lnd e7 )(C 8 Ho(Si'Pr 3 ) 2 )] +180.7, +54.2 -
[U(lnd eS )(CeH 6 (Si'Pr 3 )2)] +210.5, +209.2, -
+60.5
[U(Tp Ma2 )(C 3 H 4 (Si' ' Pr 3 ) 2 )] +175.3, +167.4, -
Table 2 Reactivity of uranium(ii!) mixed sandwich complexes with excess carbon dioxide [0053] In many of these cases, resonances are observed corresponding to free CO(g) in addition to the excess free C0 2 (g) and the product(s) obtained by reacting CO(g) with the uranium(lll) complex, thus supporting the view that the reaction of C0 2 (g) with uranium(ll!) results in liberation of (and potentially subsequent reaction of) CO(g).
[0054] In the reduction of CO gas by [U(Cp R )(C 8 H 6 (Si' ' Pr 3 ) 2 )], the identification of a reactive intermediate 'zig-zag' species which, in the presence of excess CO gas goes on to form deltate/squarate complexes, as set out in Scheme 3, indicates that, by adding an excess of other small molecules to the in situ generated 'zig-zag', a range of new species can be generated, as shown in Table 3.
δ 0 / ppm Characterised by
X-ray crystallography
[U(Cp Me5 )(CeH s (Si'Pr 3 )2)]
CO(g)+H 2 (g) +319
CO(g)+NO'(g) +250
CO(g)+NH 3 (g) +9.9, -8.8 -
[U(Cp Me4 )(C 8 H 6 (Si'Pr 3 ) 2 )]
CO(g)+NH 3 (g) +9.3, -1 1.0 -
Table 3 Reactivity of uranium(lll) mixed sandwich complexes with mixed gases
(including carbon monoxide) [0055] The reaction of [U(Cp Me5 )(C 8 H 6 (Si' ' Pr 3 )2)] with CO(g) and H 2 (g) leads to the generation of a uranium(IV) methoxide complex, as shown in Scheme 6. This compound has been characterised by X-ray crystallography.
Scheme 6 Reaction of [U(Cp a5 ){C e H e (Si i Pr 3 ) 2 }] with carbon monoxide and hydrogen
[0056] The methoxide may be liberated from this compound by quenching with Me 3 SiOTf, thereby giving Me 3 SiOMe and the uranium(IV) triflate.
[0057] The reaction of [U(Cp Me5 )(C e H 6 (Si' ' Pr 3 ) 2 )] with CO(g) and NO-(g) at -78°C in toluene led to the formation of two product species, irrespective of whether the reaction was carried out by (i) addition of CO followed by NO, or (ii) addition of NO followed by CO. Both of the species were characterised by X-ray crystallography, and it was established that the first species (1 ) incorporated two bridging-cyanate (NCO " ) groups, whilst the second (2) had a single bridging-oxo (O 2" ), as shown in Scheme 7. However, although a mixture of both products is feasible given the species involved, formation of the bridging- oxo could also occur due to ingress of oxygen into the reaction vessel.
Scheme 7 Reaction of [U(Cp Me5 ){C 8 H 6 (Si'Pr 3 ) 2 }] with nitrogen and carbon monoxides
[0058] The reaction of [U(Cp R )(C 8 H 6 (Si'Pr 3 )2)] with CO(g) and NH 3 (g) leads to the generation of product mixtures exhibiting two 3 C-labelled resonances in approximately 1 :1 ratios. These observations could be explained either by formation of a single product species containing two inequivalent carbons, or by the generation of two products in a 1 :1 ratio.
[0059] The oxocarbon derivatives generated from CO gas, which were discussed in the Applicant's previous application WO-A-2009/007755, provide valuable precursors comprising strained rings systems which, if opened, may provide suitable starting materials for the formation of complex organic molecules. However, the carbonate species which are generated from C0 2 gas in comparable reactions are of less value and it is particularly desirable to prevent the formation of carbonate, and this is achieved by the mixed gas reactions of the present invention. Thus, the compfexes [U(Cp R )(C 8 H 6 (Si'Pr 3 ) 2 )] react with a range of mixed gas systems incorporating C0 2 (g), avoiding the formation of the carbonate products, with only the hydrocarbons methane and ethane failing to prevent carbonate formation, as shown in Table 4. co 3 2 - Characterised by generation X-ray crystallography prevented lU{Cp Me5 )(C 8 H s (Si'Pr 3 ) 2 }]
C0 2 (g)+H 2 (g) +60 ✓
C0 2 (g)+NO-(g) ✓ + 143, +137
C0 2 (g)+NH 3 (g) +246.0, +88.2, +26.4, - -23.3
C0 2 (g)+CH 4 <g) -
C0 2 (g)+C 2 H 4 (g) -
C0 2 (g)+H 2 S(g) / numerous: +154
+123, +52.2, +33.0,
+30.4, +29.7, +29.1 ,
numerous: +20 - +1 1
C0 2 (g)+S0 2 (g) +143.2, +143.1 , - +137.3, +19.3, +19.2,
+18.2, +17.9, +11.8, - 19.9, -22.2
[U(Cp e4 )(C 8 H 6 (Si f Pr 3 ) 2 )]
C0 2 (g)+NO (g) +143, +137, +12, -2 -
CO<g)+NH 3 (g) +34.4 ✓
Table 4 Reactivity of uranium(ill) mixed sandwich complexes with mixed gases which comprise carbon dioxide [0060] Whilst carbonate formation was prevented In all the other cases other than with these hydrocarbons, multiple 13 C-labelled environments in varying proportions - thereby indicating multiple products - were observed for the majority of the reactions. Additionally, there was no evidence of resonances matching those observed in equivalent mixed-gas reactions with CO(g), implying that none of the carbon dioxide incorporation reactions result in liberation of, or subsequent reaction of, carbon monoxide. [0061] Two of these reactions lead to single 13 C labelled products, both of which have been identified by X-ray crystallography. In the first case, the reaction of [U(Cp Me5 ){C 8 H 6 (S! f Pr 3 ) 2 )] with C0 2 (g) and H 2 (g) leads to the generation of a product where the methyl substituents on the cyclopentadienyl rings have been activated via C-H activation and C-C bond formation to bridging C0 2 units, leading to a di-uranium(IV) 'tuck- in' complex, as illustrated in Scheme 8.
Scheme 8 Reaction of [U(Cp M05 ){C 8 H 6 (Si'Pr 3 ) 2 }] with carbon dioxide and hydrogen
[0062] It is proposed that generation of the 'tuck-in' occurs via generation of highly reactive bridging formate {OC(H)Cr} groups, and subsequent σ-bond metathesis, resulting in C-C bond formation and elimination of dihydrogen.
[0063] The second reaction which, as evidenced by 13 C NMR spectroscopy, produces a single product is the reaction of [U(Cp Me4 )(C 8 H 6 (Si'Pr 3 ) 2 )] with carbon dioxide and ammonia, as shown in Scheme 9,
Scheme 9 Reaction of [U(Cp Me4 ){C 8 He(Si'Pr 3 ) 2 )3 with carbon dioxide and ammonia
[0064] An X-ray crystal structure of this product has been obtained, and this has identified the product as a di-uranium(IV) complex with a single bridging C0 2 NH z~ unit (Figure 4a). The bridging C0 2 NH 2" fragment is a doubly deprotonated derivative of carbamic acid (H 2 NCOOH); the singly deprotonated H2NCOO- could also act as a terminal or bridging iigand. Hence, a combination of the various bridging modes of deprotonated carbamic acid could explain the multiple products obtained from the reaction of [U(Cp Me5 )(C 3 H 6 (Si i Pr 3 )2)] with carbon dioxide and ammonia.
Electrochemical Studies
[0065] The inventors have utilised analytical electrochemistry, specifically cyclic voltammetry, in order to investigate the redox behaviour of the uranium(lll) mixed- sandwich complexes, along with samples of fully characterised mono- and di-uranium(IV) complexes which have been isolated.
[0066] Thus, cyclic voltammograms have been obtained for many of the uranium(ill) mixed-sandwich complexes [U(L')(L")(thf) n ]. The U"VU I oxidation has been observed as an irreversible wave at ca. +0.7 V vs. ferrocene for complexes where L" is the cyc!ooctatetraene ligand, or ca. +0.35 V vs. ferrocene for complexes where L" is the pentalene ligand. Values of redox potentials are set out in Table 5 and a typical cyclic voltammogram is shown in Figure 4.
Complex Ep(ox) {U} / V £ p (red) {U'}/ V
[U(Cp Me5 )(C 6 HQ(S!' ' Pr3)2){thf)] +0.65 -
[U(Cp M94 )(C 8 He(Si' ' Pr 3 ) 2 )(thf)] +0.62 -0.80
[U(ind Me7 )(C 8 H 6 <Si'Pr 3 )2)] +0.71 -0.87
[U(lnd Me6 )(C 8 H 6 (Si'Pr 3 ) 2 )] +0.84 -0.88
[U(Tp Me2 )(C 8 H s (Si'Pr 3 ) 2 )] - -
[U(Cp Me5 )(C a H 4 (Si'Pr 3 )2)] ca. +0.34 -
[U(Tp)(C e H 4 (Si'Pr 3 ) 2 )] ca. +0.39 -
[U(Tp Me2 )(C 8 H 4 (Si'Pr 3 ) 2 )] +0.40 -
Table 5 Electrochemical data for mono-uranium(lll) mixed sandwich complexes
[0067] The irreversibility of the redox waves (at all scan rates) indicates that the uranium(IV) species [U(L')(L")(thf) n ] + are not stable on the electrochemical timescale (ca. 1 sec). Voltammograms of [U(Cp Me4 )(C 8 H 6 (Si'Pr 3 ) 2 )(thf)], [U(ind Me7 )(C 8 H 6 (Si'Pr 3 ) 2 )] and [U(lnd eB )(C e H 6 {Si'Pr 3 )2)] , however, do show distinct product reduction waves, due to a single decomposition product of [U(L')(CeH 6 {Si i Pr 3 )2)(thf) f ,] + which is both redox active and stable on a timescafe of ca. 10 sec.
1.0 06 00 -0.5 -1,0 -1.5 -2,0
Figure 4 Cyclic voltammogram of [U(lnd Me7 )(C 8 H 6 (Si'Pr 3 )2)3, showing both the irreversible oxidation wave {·) and the product reduction wave (♦)
[0068] As the oxidation potentials of the uranium(lil) species become less positive, these species can be viewed as a stronger reducing agent; however, their potentials are much more positive than most standard reducing agents.
[0069] Cyclic voltammograms of the di-uranium(IV) oxocarbon and carbonate complexes have been obtained by two methods - either the synthesis and use of an analytically pure sample of the test species, or obtaining voltammograms of a 'crude' sample of the test species which had been generated in situ. The latter method is believed to be more representative of the electrochemical system that would result during buik/preparative electrochemical processes.
[0070] From the available cyclic voltammograms of four isolable di-uranium(IV) complexes, it has been observed that the deltate complex [{U(Cp eS )(C 8 H6(Si'Pr3)2)}2(C 3 0 3 )] showed a single irreversible reduction wave at -2.44 V vs. ferrocene, along with a significant number of ill-defined product oxidation waves, as can be seen from Figure 5. This indicates that the [U(C 3 0 3 )U] 5+ (formally a U IV and U m centre) species generated upon reduction is unstable on the electrochemical timescale (< 1 sec.) and rapidly decomposes/fragments, thereby giving multiple redox active species.
10071] The squarate complex similarly has a single irreversible reduction wave at -2.81 V vs. ferrocene, along with associated product oxidation waves, However, a distinctive irreversible oxidation wave was also observed at +0.75 V vs. ferrocene, which could be due to oxidation of the squarate i.e. [U(C40 4 )U] 6+ 7* , or an impurity (not the uranium(ll l) mixed-sandwich precursor) in the sample, The carbonate complexes [{U(Cp R )(CaH 6 (Si f Pr 3 ) 2 )} 2 (C0 3 )] are both redox inactive over the solvent window for the conditions in use (i.e. E p (red) > -2.9 V vs. ferocene). Data for the di-uranium(IV) mixed sandwich complexes are presented in Table 6,
Complex E p {red) / V
[{U(Cp Me5 )(C 8 He(Si'Pr 3 ) 2 )} 2 (C303)] -2.44
[{U(Cp Me )(C8H 6 (Si f Pr3) a )}2(C404)] "2.81
[{U(Cp Me5 )(C 8 H e (Si'Pr 3 ) 2 )} 2 (C0 3 )] > -2.9
[{U(Cp Me4 )(C 8 H 6 (Sl'Pr 3 ) 2 )} 2 (C0 3 )] > -2.9
Table 6 Electrochemical data for di-uranium(IV) mixed sandwich complexes [0072] The less negative potential required for reduction of the deltate/squarate species compared to the carbonates, implies that it should be possible for selective reduction (and subsequent decomposition) of the oxocarbon containing di-uranium(!V) species from a mixture of the two, such as those obtained by reaction of [U(Cp R )(C 3 H 6 (Si'Pr 3 )2)] with C0 2 (g).
[0073] Cyclic voltammograms of the mono-uranium(iV) complexes [U(Cp Ma5 )(C 8 H 6 (Si'Pr 3 ) 2 )CI] and [U(Cp e5 )(C 3 H 6 (Si'Pr 3 )2)(OMe)] are presented in Figures 6 and 7 and show waves corresponding to semi-reversible oxidation of the U I /U'" redox couples (Table 7), thereby indicating that their uranium(lll) analogues, i.e. [U(Cp Me5 )(C 8 He(Si i Pr 3 ) 2 )X] ^ , were stable on the electrochemical timescaie (ca. 3 sec). Additionally the U I /U V redox couple is observed in the voltammogram of the uranium(IV) methoxide as a semi-reversible wave, indicating the uranium(V) species [U(Cp Ma5 )(CeH 6 (Si'Pr 3 ) 2 )(OMe)] + is also stable on the electrochemical timescaie (ca. 6 sec).
Figure 6 Cyclic Voltammogram of [U(Cp Me5 )(C 8 H e (Si' ' Pr 3 )2)CI]
Complex U IV / U 1 " U I / U v
E p (red) E p (ox) (p (ox) / E p (ox) £ p (red) ip(ied) / / V / V / d > / / V v ox)
[U(Cp Ma5 )(C 8 H e (Si'Pr 3 ) 2 )Ci] ^22 -2.13 0.66 - - -
[U(Cp e5 )(C s H6(Si' ' Pr 3 )2)(OMe)] -2.82 -2.73 - † -0.35 -0.42 0.81
† due to the proximity of the redox wave to the limit of the solvent window, the peak current ratio cannot be accurately measured
Table 7 Electrochemical data for mono-uranium(IV) mixed sandwich complexes
Figure 7 Cyclic Voltammogram of [U{Cp Me5 )(C 8 H e (Si' ' Pr 3 )2)(OMe)]
[0074] As previously disclosed, the present inventors envisage the treatment of gas- metal complexes in order to obtain organic chemical intermediates, so that the invention provides a method for the production of organic chemical compounds, said method comprising the treatment of the gas-metal complexes of the third aspect of the invention.
[0075] In preferred embodiments of the invention, this treatment comprises electrochemical treatment of said gas-metal complexes and, in this context, bulk electrochemical techniques - specifically involving controlled potential electrolysis - have been used to electrochemically reduce samples of the di-uranium(IV) deltate and squarate complexes by applying a reductive potential (ca. 0.25 V more negative than the reduction potential of the species of interest) between gold and platinum mesh electrodes through a ["Bu N][B(C 6 F5 ]/tetrahydrofuran solution containing the species of interest.
[0076] It has been observed that solutions of both the deltate and squarate complexes undergo colour changes upon eiectrochemical reduction (with associated currents of ca. 5 mA), thereby changing from the orange-red colour indicative of di-uranium(IV) complexes to a brown colour, generally corresponding to uranium(lll) complexes. Cyclic voltammograms obtained before, during and after the electrochemical reductions have confirmed the loss of the irreversible reduction wave associated with the di-uranium(iV) oxocarbon species,
[0077] However, multiple irreversible oxidation waves were observed following reduction of the oxocarbon species (for the deltate, £ p (ox) = +0,64, +0.84 5 V vs ferrocene, and for the squarate, £ p (ox) = +0.64, +0.90 § , +1 ,21 s V vs ferrocene ( with associated product reduction waves at E p (red) * -0.8 V vs ferrocene)). Additionally following the reduction of the squarate, an irreversible reduction wave is observed at E p (red) - -1 ,83 V vs ferocene, This redox process was observed even following further applications of sufficient reductive potentials, implying that if the associated species is reduced, it must be rapidly regenerated by reaction with other species present.
[0078] Following the electrochemical reduction of the squarate, there were significant amounts of black-brown deposits on the platinum counter electrode (which did not occur for the reduction of deltate). Characterisation of these deposits by diffuse reflectance IR spectroscopy allowed for the identification of two major regions of absorbance, 2950-2850 cm "1 and 1480-1360 cm "1 ; these regions respectively correspond to C-H and C-C stretches, whilst carbonyl bands are commonly observed in the range of 1600-2200 cm '1 . However, it could be possible for more complex vibrations of the oxocarbons (or their derivatives) to occur at lower energies than simple carbonyl groups.
[00793 The method according to the first aspect of the present invention provides an efficient and convenient means for the removal of gases such as the oxides of carbon, nitrogen and sulphur from the atmosphere through their reaction with the metal complexes, including those according to the second aspect of the invention. Accordingly, the method according to the first aspect of the invention is particularly useful in the removal of so- called greenhouse gases from the atmosphere, and is therefore of potentially very great value environmentally.
[0080] Furthermore, the method of the second aspect of the invention provides a convenient and potentially extremely valuable route for the production of a range of synthetically useful products from the reaction products of these gases with metal complexes, thereby offering an alternative route for the production of chemical intermediates which does not rely on further utilising limited natural reserves of oil. In addition, the invention provides a valuable means for the use of reserves of depleted uranium for the manufacture of useful products.
Experimental Details
Reaction of rU(Cp R )(C«H R /Si'Prg) ? Vl with mixed gases
[0081] The solvent free U'" complex was generated by heating the solvated complex [U(Cp R )(C 8 H 6 (Si'Pr 3 )2)(thf)] to 110°C under a vacuum of ca. 10 "5 mbar for 45 minutes, thereby changing the purple crystalline solid into a brown-black semi-crystalline solid. This material was dissolved in ca. 0.5 cm 3 toluene, cooled to -77°C (dry ice/acetone) and put under a static vacuum of ca, 1 Q -5 mbar. Accurately measured amounts of gases were added to the reaction vessel (of known volume) via a mercury-piston (Toepler) pump (generally one equivalent of 13 C labelled CO(g) or C0 2 (g), and between one and three equivalents of the other gas(es)). The reaction mixture was slowly warmed to room temperature, usually giving a dark red solution,
Electrochemistry
[0082] Analytical electrochemical studies (cyclic voltammetry) were carried out using a three-electrode cell under an atmosphere of thf-saturated argon, with data collection using a BASi Epsilon-EC potentiostat under computer control. The working electrode was a gold (2.0 mm 2 ) disc and the counter electrode a platinum wire. A second platinum wire was used as a pseucfo-reference electrode, with potentials calibrated in situ by addition of ferrocene and use of the [FeCp 2 ] 0 1+ redox couple as an internal standard. Sample solutions were ca. 1 pmoi.cm "3 in the test compound with 50 pmol.cm "3 [ rt Bu 4 N][B(CeF 5 )4] as the supporting electrolyte in thf solvent. Under these conditions the maximum solvent window is +1.5 to -2,9 V vs. [FeCp 2 ].
[0083] Bulk electrochemical experiments (controlled potential electrolysis) were carried out under an atmosphere of thf-saturated argon in a custom built cell fitted with five electrodes; gold and platinum mesh (ca. 4 cm 2 each) working and counter electrodes for bulk electrochemical experiments, a platinum wire separated from the bulk solution by a course glass sinter as a pseudo-reference electrode, along with a gold disc (2.0 mm 2 ) and platinum wire working and counter electrodes for analytical electrochemical experiments (used to monitor the progress of bulk redox processes). Potentials for bulk experiments were applied by a BASi PWR-3 high power potentiostat. Solutions were ca. 1 pmol.cm "3 in the species of interest and 50 pmol.cm "3 ["Bu4N][B(C 6 F 5 ) ] for the supporting electrolyte in thf solvent.
[0084] The present invention will now be further illustrated, though without in any way limiting its scope, by reference to the following Examples.
Examples
Example 1 - Synthesis of iUfn-CMSfPr 1 )(n-Cp*} (u-OCN (1)
[0085] A sample of black, crystalline [U(n-C B H e {Si l Pr3-1 l 4}2)(n-Cp*)](THF) (400 mg, 4.64 x 10 "4 mol) was placed in an ampoule (high-vacuum PTFE stopcock, 50 mL volume) and heated under vacuum ( 10°C/1 x 10 "5 mbar) for 1 hour. The desolvated material was dissolved in d 6 -toluene (0,5 mL). The solution was cooled to -78°C, the headspace evacuated and 13 CO (0.07 bar, 1.55 x 10 "4 mol) was admitted followed by NO (0.07 bar, 1.55 x 10 ~4 mol). The flask was warmed to ambient temperature, resulting in a change in colour to red-brown. Cooling to 4°C for 1 week gave the product as black crystals {the supernatant was kept aside for isolation of the second reaction product). The product was rinsed with pentane (2 mL) at -78°C and dried in vacuo to afford the title compound as black prisms suitable for single crystal X-ray diffraction (52 mg, 40% based on starting [Uin-CeHeiSrPra-I^Xn-Cp^ THF)).
[0086] Ή NMR (C 6 D 5 CD 3 , 303 K): δ ppm 52.3 (s, 4H, COT ring-CH), 6.84 (s, br, 30H, Cp*-CH 3 ), -7.45 (36H, s, br, 'Pr-CHs), -8.75 (12H, s, br, 'Pr-CW), -9.26 (36H, s, br, 'Pr- CH 3 ), -54.3 (s, 4H, COT ring-CH), -91.6 (s, 4H, COT ring-CH). 13 C NMR (C 6 D 5 CD 3l 303 K, selected data): δ ppm 249.3.
MS (El): m/z = 833 (100 %, -CeHeiSi'Pra-l ,4} 2 ){r]-Cp*)U(0 13 CN)] + ).
Anal. Calcd. (found) for
1 C and C 53.46 (53.27), H 7.62 (7.57), N 1.68 (1.83). Example 2 - Synthesis of iU(n-CMSlPr 1,4 )(n-Co*)h(u-0) (2)
[0087] The supernatant from the crystallisation of complex 1 was reduced to dryness in vacuo. The solid mass was taken up in 'BuOMe (1 mL) and kept at 4°C overnight. A smali crop of red-brown crystals suitable for single crystal X-ray diffraction were separated from the mother liquor and washed with 'BuOMe (2 mL) at -78°C, Drying in vacuo gave the title compound in an unoptimised yield of 22 mg (9 %).
[0088] 1 H NMR (C e D 5 CD 3 , 303 K): 5 ppm 19 (s, 2H, COT ring-CH), 113 (s, 2H, COT ring-CH), 6.94 (18H, d, 'Pr-CHs), 6.53 (6H, m, br, ! Pr-CH), 3.30 (br s, 30H, Cp*-CH 3 ), 0.74 (18H, d, 'Pr-CHs), -0.59 (18H, d, 'Pr-CHs), -2.40 (6H, m, br, 'Pr-CH), -7.37 (18H, d, 'Pr-CH 3 ), -81.4 (s, 2H, COT ring-CH), -85.9 (s, 2H, COT ring-CH), -1 1 (s, 2H, COT ring-CH), -116 (s, 2H, COT ring-CH).
MS (El): mfz = 808 (10 %, [(η~0 8 Η 6 {3ΓΡΓ 3 -1 ,4} 2 )(η-Ορ * )υ(0)] + ).
[0089] Throughout the description and claims of this specification, the words "comprise" and "contain" and variations of them mean "including but not limited to", and they are not intended to (and do not) exclude other moieties, additives, components, integers or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.
[0090] Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed In this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.
[0091] The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.