HYDROGENATION CATALYST Field of the Invention The present invention relates to zinc complexes and methods of manufacturing such complexes. The invention also relates to the use of such complexes in methods of selective hydrogenation of compounds containing reducible double or triple bonds and intermediates in such methods. Background of the Invention Alkynes are important starting materials in organic synthesis, particularly in the synthesis of bioactive compounds which contain carbon-carbon double bonds having a well-defined configuration. Non-limiting examples of such bioactive compounds include β-carotene, polyene antifungal drugs, crocaine, polyunsaturated fatty acids (PUFAs), pheromones and cruentaren. The stereoselective hydrogenation of alkynes to alkenes is an atom-economical method of synthesis of the carbon-carbon double bonds in these molecules. The most widely used method for the selective hydrogenation of alkynes employs the Lindlar catalyst in heterogeneous catalysis. The Lindlar catalyst consists of Pd (5%) deposited on CaCO3, treated with lead acetate. The lead acetate poison is used to improve the cis/trans selectivity of the catalyst. Hydrogenation with the Lindlar catalyst is therefore highly stereoselective, producing almost exclusively the (Z)-isomer. Despite the effectiveness of the Lindlar catalyst in such syntheses, there is a need for alternative stereoselective catalysts useful in the hydrogenation of alkynes to prepare carbon-carbon double bonds, due in part to the high relative cost of the Pd metal present in the catalyst and also to the toxicity of the Pb catalyst poison used in the Lindlar catalyst. Such catalysts may find use in a wide range of applications in addition to the reduction of alkynes to alkenes. For example, such hydrogenation catalysts may also find use in the reduction of other functional groups containing reducible double or triple bonds, including but not limited to alkenes, nitriles, carbonyls (including aldehydes and ketones), esters and amides. The present invention was developed with a view to providing alternative hydrogenation catalysts to address or ameliorate one or more of the problems mentioned above. Summary of the Invention A first aspect of the invention is a compound according to formula (I): (I) or a salt, solvate or hydrate thereof; wherein: Y is selected from -QR ¹ R ² , and OR ^F ; wherein Q is selected from N, P and P(=O); L is selected from -CR ⁸ -CR ⁹ -CR ¹⁰ -, -CR ⁵ -, -CR ⁶ -CR ⁷ -, -CR ^N3 -NR ^G -CR ^N4 - and -CR ^O1 -O-CR ^O2 -; either: (A) R ¹ is R ^1A , R ² is R ^2A and R ⁴ is R ^4A ; or (B) R ⁴ is R ^4A ; and R ¹ and R ² together with the Q moiety to which they are attached are joined to form a 3-6 membered heterocyclic group optionally substituted with one or more groups R ^E ; or (C) R ¹ is R ^1A ; and R ² , R ⁴ and the atoms to which they are attached form a 5-8 membered heterocyclic group, optionally substituted with one or more groups R ^D , and optionally being fused to one or more optionally substituted aryl groups; R ³ is selected from H; linear or branched unsubstituted C _1-12 aliphatic groups; C ₆ aryl, optionally substituted with one or more groups R ^A , and 5-6 membered heteroaryl, optionally substituted with one or more groups R ^B ; R ⁵ , R ⁶ , R ⁷ , R ^N3 , R ^N4 , R ^O1 and R ^O2 are each independently selected from H, linear or branched unsubstituted C _1-12 aliphatic groups, C _5-6 unsubstituted aryl or heteroaryl groups, and -NR ^N1 R ^N2 ; R ⁸ , R ⁹ and R ¹⁰ are each independently selected from H, linear or branched unsubstituted C _1-12 aliphatic groups, C _5-6 unsubstituted aryl or heteroaryl groups, and -NR ^N1 R ^N2 ; or two or more of R ⁸ , R ⁹ and R ¹⁰ , together with the atoms to which they are attached, are joined to form a monocyclic or bicyclic group, with any remaining groups of R ⁸ , R ⁹ and R ¹⁰ being selected from H, linear or branched unsubstituted C _11--44 aliphatic groups, C _5-6 unsubstituted aryl or heteroaryl groups, and -NR ^N1 R ^N2 ; R ^1A , R ^2A and R ^4A are each independently selected from H; linear or branched unsubstituted C _1-12 aliphatic groups; C ₆ aryl, optionally substituted with one or more groups R ^A ; 5-6 membered heteroaryl, optionally substituted with one or more groups R ^B ; C _6-20 aralkyl, optionally substituted with one or more groups R ^C ; and Si(C _1-6 alkyl) ₃ ; R ^N1 and R ^N2 are each independently selected from linear or branched unsubstituted C _1-6 aliphatic groups, or R ^N1 and R ^N2 together with the N atom to which they are attached are joined to form a 3-6 membered heterocyclic group optionally substituted with one or more groups R ^E ; R ^A , R ^B , R ^C , R ^D and R ^E are each independently selected from linear or branched unsubstituted C _1-6 aliphatic groups; halo; O(C _1-6 alkyl); -CF ₃ , -CF ₂ H, -CFH ₂ ; -OCF ₃ , -OCF ₂ H and -OCFH ₂ ; R ^F and R ^G are independently selected from H; C _1-12 alkyl groups; C ₆ aryl, optionally substituted with one or more groups R ^A ; 5-6 membered heteroaryl, optionally substituted with one or more groups R ^B ; C _6-20 aralkyl, optionally substituted with one or more groups R ^C ; -S(=O) ₂ CF ₃ ; and -C(=O)R ^H , wherein R ^H is linear or branched C _1-6 alkyl optionally substituted with one or more groups independently selected from OH and halo; with the proviso that the compound is not a compound according to formula (X): (X) wherein the group XX is selected from -N(SiMe ₃ ) ₂ and -NH(DIPP); and wherein DIPP is the group: It has been found that the zinc center facilitates the activation of dihydrogen through a 1,2-addition across the Zn-Y bond. The compounds therefore provide effective catalysts for the reduction of a wide range of compounds with functional groups containing reducible double or triple bonds. In particular, the compounds provide effective catalysts for the chemo- and stereo-selective semi-hydrogenation of alkynes to (Z)-alkenes. Herein, “semi- hydrogenation” refers to the hydrogenation of alkynes to alkenes, i.e. with little or no overhydrogenation to the alkane. The compounds have been found to facilitate the production of alkenes from alkynes at relatively high yield, in a chemo- and stereo-selective manner. In particular, catalysts comprising the compounds provide for preferential synthesis of the alkene without over- reduction to the alkane, and also provide for stereoselective production of (Z)-alkenes. A second aspect of the invention is a catalyst comprising a compound according to the first aspect. In some embodiments, the catalyst is a hydrogenation catalyst. In some embodiments, the catalyst is an alkyne hydrogenation catalyst. A third aspect of the invention is a method of reducing or hydrogenating a double or triple bond in the presence of a catalyst comprising a compound according to the first aspect. A fourth aspect is a method of activating dihydrogen for hydrogenation, comprising reacting dihydrogen with a catalyst comprising a compound according to the first aspect. A fifth aspect is a compound according to formula (VII): (VII) wherein L, R ³ and R ⁴ are as defined above under the first aspect; and R ¹¹ and R ¹² are each independently selected from (hetero)hydrocarbyl groups. In some embodiments R ¹¹ and R ¹² are each independently selected from alkyl and aryl groups. In some embodiments, R ¹¹ and R ¹² are each independently selected from linear or branched unsubstituted C _1-6 alkyl, and C _3-8 aromatic or heteroaromatic groups. However, the skilled person will understand that the hydrogenation may be carried out on any alkyne regardless of the identity of the groups R ¹¹ and R ¹² , such that R ¹¹ and R ¹² may be selected from any suitable alkyne substituent. A sixth aspect of the invention is a method of preparing an intermediate according to formula (VII):

(VII) the method comprising reacting an alkyne according to formula (V): (V) with dihydrogen (H ₂ ) in the presence of a catalyst comprising a compound according to formula (I): (I) or a salt, solvate or hydrate thereof; wherein L, Y, R ³ and R ⁴ , are as defined above under the first aspect; and R ¹¹ and R ¹² are as defined under the fifth aspect. A seventh aspect of the invention is therefore a method of preparing an alkene according to formula (VI): (VI) the method comprising protonating a compound according to formula (VII):

(VII) wherein L, R ³ and R ⁴ are as defined above under the first aspect; and R ¹¹ and R ¹² are as defined under the fifth aspect. An eighth aspect of the invention is a method of making a compound according to formula (I): 3 (I) from starting materials comprising a compound according to formula (II): (II) wherein Y, L, R ³ and R ⁴ are as defined above under the first aspect. A ninth aspect of the invention is an intermediate according to formula (IV):

(IV) wherein L, R ³ and R ⁴ are as defined above under the first aspect and X is a monovalent anion. A tenth aspect of the invention is a method of making an intermediate according to formula (IV): (IV) comprising reacting a compound according to formula (III) with ZnX ₂ (III) wherein L, R ³ and R ⁴ are as defined above under the first aspect, M is a metal atom selected from Li, Na and K, and X is as defined under the ninth aspect. The skilled person will understand that the structure according to formula (III) is one possible representation of such compounds, but that in some cases the compound may adopt a configuration in which the M atom is bound to both N atoms to form a cyclic system. An eleventh aspect of the invention is a method of making a compound according to formula (I): 3 (I) from a compound according to formula (IV): (IV) wherein Y, L, R ³ and R ⁴ are as defined in the first aspect, and X is a monovalent anion. A twelfth aspect of the invention is a method of making a compound according to formula (VIII): (VIII) comprising reacting a compound according to formula (I): 3 (I) with dihydrogen (H ₂ ), wherein L, Y, R ³ and R ⁴ are as defined under the first aspect. The method according to the twelfth aspect may be used to prepare the hydride analogue (VIII) of the catalytic complex according to formula (I) in situ. The hydride analogue (VIII) may then go on to react with a compound containing a reducible double or triple bond which is present in the reaction mixture, e.g. an alkyne, in a first step towards semi-hydrogenation of the alkyne. A thirteenth aspect of the invention is the use of a compound according to the first aspect or catalyst according to the second aspect in a hydrogenation process, for example an alkyne hydrogenation process. Another aspect us the use of a compound according to the first aspect as a catalyst a hydrogenation process, for example an alkyne hydrogenation process. Definitions Unless otherwise specified, the term “substituted” as used herein, pertains to a parent group which bears one or more substituents. The term “substituent” is used herein in the conventional sense and refers to a chemical moiety which is covalently attached to, or if appropriate, fused to, a parent group. A wide variety of substituents are well known, and methods for their formation and introduction into a variety of parent groups are also well known. The term “C4-20 aliphatic” as used herein, pertains to a monovalent moiety obtained by removing a hydrogen atom from a carbon atom of a hydrocarbon compound having from 4 to 20 carbon atoms, which may be saturated or unsaturated (e.g. partially unsaturated, fully unsaturated). The term “C _1-4 aliphatic” as used herein, pertains to a monovalent moiety obtained by removing a hydrogen atom from a carbon atom of a hydrocarbon compound having from 1 to 4 carbon atoms, which may be saturated or unsaturated (e.g. partially unsaturated, fully unsaturated). Thus, the term “aliphatic” includes the sub-classes alkyl, alkenyl, alkynyl, cycloalkyl, etc. The term “C _1-12 alkyl” as used herein, pertains to a monovalent moiety obtained by removing a hydrogen atom from a carbon atom of an aliphatic, acyclic hydrocarbon compound having from 1 to 12 carbon atoms, which is saturated. The term “C _1-4 alkyl” as used herein, pertains to a monovalent moiety obtained by removing a hydrogen atom from a carbon atom of an aliphatic, acyclic hydrocarbon compound having from 1 to 4 carbon atoms, which is saturated. Examples of saturated alkyl groups include, but are not limited to, methyl (C ₁ ), ethyl (C ₂ ), propyl (C ₃ ), butyl (C ₄ ), pentyl (C ₅ ), hexyl (C ₆ ), heptyl (C ₇ ) and octyl (C ₈ ). Examples of saturated linear alkyl groups include, but are not limited to, methyl (C ₁ ), ethyl (C2), n-propyl (C3), n-butyl (C ₄ ), n-pentyl (amyl) (C ₅ ), n-hexyl (C ₆ ), n-heptyl (C7) and n-octyl (C8). Examples of saturated branched alkyl groups include iso-propyl (C3), iso-butyl (C ₄ ), sec-butyl (C ₄ ), tert-butyl (C ₄ ), iso-pentyl (C ₅ ), and neo-pentyl (C ₅ ). Aryl: The term “C ₆ aryl” or “6-membered aryl”, as used herein, pertains to a monovalent moiety obtained by removing a hydrogen atom from an aromatic ring atom of an aromatic compound, which moiety has 6 ring carbon atoms. The term “aryl” as used herein refers to carboaryl moieties, i.e. does not include heteroaryl moieties. Examples of aryl groups include, but are not limited to, phenyl, naphthyl, tolyl and xylyl. Heteroaryl: The term “6-membered heteroaryl”, as used herein, pertains to a monovalent moiety obtained by removing a hydrogen atom from an aromatic ring atom of an aromatic compound, which moiety has 6 ring atoms, one or more of those ring atoms being a heteroatom. Heterocyclyl: The term “6-membered heterocylyl” or “6-membered heterocylic group”, as used herein, pertains to a monovalent moiety obtained by removing a hydrogen atom from a ring atom of a heterocyclic compound, which moiety has 6 ring atoms, one or more of those ring atoms being a heteroatom (Hetero)hydrocarbyl: The term “(hetero)hydrocarbyl”, as used herein, includes hydrocarbyl and heterohydrocarbyl groups. The term “hydrocarbyl”, as used herein, pertains to a monovalent moiety obtained by removing a hydrogen atom from a hydrocarbon compound. Thus, the term “hydrocarbyl” includes the sub-classes aliphatic, aromatic, alkyl, alkenyl, alkynyl, cycloalkyl, etc. The term “heterohydrocarbyl”, as used herein, pertains to a monovalent moiety obtained by removing a hydrogen atom from a hydrocarbon compound which also contains heteroatoms, e.g. a heteroaromatic compound, heterocyclic compound or a heteroaliphatic compound. Aralkyl: The term “C _6-20 aralkyl”, as used herein, pertains to a monovalent moiety obtained by removing a hydrogen atom from a pendent alkyl group of an alkyl-substituted aromatic ring, wherein the total number of carbon atoms in the monovalent moiety is between 6 and 20. In other words, an aralkyl group is an aryl-substituted alkyl radical. Non-limiting examples of aralkyl groups include benzyl and α-phenylbenzyl (alpha-phenylbenzyl). Description of the drawings Figure 1 shows a DFT-calculated Gibbs Free Energy profile for H ₂ activation by a compound according to the invention, at standard conditions using the M06L functional and hybrid base-set, with energies provided in kcal mol ^-1 . Figure 2 shows initial and final ¹ H NMR spectra for the protonolysis reaction of (DippBDI)ZnC(Ph)CHPh using aniline. Figure 3 shows initial and final ¹ H NMR spectra for cis-stilbene hydrozincation reaction using (DippBDI)ZnH. Figure 4 shows initial and final ¹ H NMR spectra for trans-stilbene hydrozincation reaction using (DippBDI)ZnH. Figure 5 shows the crystal structure of ( ^Dipp BDI)ZnC(Ph)CHPh as determined by X-ray crystallography, with 50% probability ellipsoids. Detailed Description Preferred and/or optional features of the invention will now be set out. Any aspect of the invention may be combined with any other aspect of the invention unless the context demands otherwise. Any of the preferred and/or optional features of any aspect may be combined, either singly or in combination, with any aspect of the invention unless the context demands otherwise. A first aspect of the invention is a compound according to formula (I): (I) or a salt, solvate or hydrate thereof; wherein: Y is selected from -QR ¹ R ² and OR ^F ; wherein Q is selected from N, P and P(=O); L is selected from -CR ⁸ -CR ⁹ -CR ¹⁰ -, -CR ⁵ -, -CR ⁶ -CR ⁷ -, -CR ^N3 -NR ^G -CR ^N4 - and -CR ^O1 -O-CR ^O2 -; either: (A) R ¹ is R ^1A , R ² is R ^2A and R ⁴ is R ^4A ; or (B) R ⁴ is R ^4A ; and R ¹ and R ² together with the Q moiety to which they are attached are joined to form a 3-6 membered heterocyclic group optionally substituted with one or more groups R ^E ; or (C) R ¹ is R ^1A ; and R ² , R ⁴ and the atoms to which they are attached form a 5-8 membered heterocyclic group, optionally substituted with one or more groups R ^D , and optionally being fused to one or more optionally substituted aryl groups; R ³ is selected from H; linear or branched unsubstituted C _1-12 aliphatic groups; C ₆ aryl, optionally substituted with one or more groups R ^A , and 5-6 membered heteroaryl, optionally substituted with one or more groups R ^B ; R ⁵ , R ⁶ , R ⁷ , R ^N3 , R ^N4 , R ^O1 and R ^O2 are each independently selected from H, linear or branched unsubstituted C _1-12 aliphatic groups, C _5-6 unsubstituted aryl or heteroaryl groups, and -NR ^N1 R ^N2 ; R ⁸ , R ⁹ and R ¹⁰ are each independently selected from H, linear or branched unsubstituted C _1-12 aliphatic groups, C _5-6 unsubstituted aryl or heteroaryl groups, and -NR ^N1 R ^N2 ; or two or more of R ⁸ , R ⁹ and R ¹⁰ , together with the atoms to which they are attached, are joined to form a monocyclic or bicyclic group, with any remaining groups of R ⁸ , R ⁹ and R ¹⁰ being selected from H, linear or branched unsubstituted C _1-4 aliphatic groups, C _5-6 unsubstituted aryl or heteroaryl groups, and -NR ^N1 R ^N2 ; R ^1A , R ^2A and R ^4A are each independently selected from H; linear or branched unsubstituted C _1-12 aliphatic groups; C ₆ aryl, optionally substituted with one or more groups R ^A ; 5-6 membered heteroaryl, optionally substituted with one or more groups R ^B ; C _6-20 aralkyl, optionally substituted with one or more groups R ^C ; and Si(C _1-6 alkyl) ₃ ; R ^N1 and R ^N2 are each independently selected from linear or branched unsubstituted C _1-6 aliphatic groups, or R ^N1 and R ^N2 together with the N atom to which they are attached are joined to form a 3-6 membered heterocyclic group optionally substituted with one or more groups R ^E ; R ^A , R ^B , R ^C , R ^D and R ^E are each independently selected from linear or branched unsubstituted C _1-6 aliphatic groups; halo; O(C _1-6 alkyl); CF ₃ , -CF ₂ H, -CFH ₂ ; -OCF ₃ , -OCF ₂ H and -OCFH ₂ ; R ^F and R ^G are independently selected from H; C _1-12 alkyl groups; C ₆ aryl, optionally substituted with one or more groups R ^A ; 5-6 membered heteroaryl, optionally substituted with one or more groups R ^B ; C _6-20 aralkyl, optionally substituted with one or more groups R ^C ; -S(=O) ₂ CF ₃ ; and -C(=O)R ^H , wherein R ^H is linear or branched C _1-6 alkyl optionally substituted with one or more groups independently selected from OH and halo; with the proviso that the compound is not a compound according to formula (X): (X) wherein the group XX is selected from -N(SiMe ₃ ) ₂ and -NH(DIPP); and wherein DIPP is the group: The group Y Y is selected from -QR ¹ R ² and OR ^F . In some embodiments, Y is -QR ¹ R ² . In some embodiments, R ^F is selected from linear unsubstituted C _1-4 alkyl groups. In some embodiments, R ^F is methyl. In some embodiments, Y is selected from one of the following groups: The group Q In preferred embodiments, Y is -QR ¹ R ² . The group Q is selected from N, P and P(=O). In some embodiments, Q is N. Thus in some embodiments, the group -QR ¹ R ² is -NR ¹ R ² . In some embodiments, Q is P. Thus in some embodiments, the group -QR ¹ R ² is -PR ¹ R ² . In some embodiments, Q is P(=O). Thus in some embodiments, the group -QR ¹ R ² is -P(=O)R ¹ R ² . In some embodiments, the group -QR ¹ R ² is selected from one of the following groups: The group L L is selected from -CR ⁸ -CR ⁹ -CR ¹⁰ -, -CR ⁵ -, -CR ⁶ -CR ⁷ -, -CR ^N3 -NR ^G -CR ^N4 - and -CR ^O1 -O-CR ^O2 -. In some embodiments, L is selected from -CR ⁸ -CR ⁹ -CR ¹⁰ -, -CR ⁵ - and -CR ⁶ - CR ⁷ -. In some embodiments, L is -CR ⁸ -CR ⁹ -CR ¹⁰ -. Thus in some embodiments, the compound is a compound according to formula (IA): (IA) or a salt, solvate or hydrate thereof. In some embodiments of formula (IA), Y is QR ¹ R ² . In some embodiments, L is -CR ⁸ -CR ⁹ -CR ¹⁰ -, Y is QR ¹ R ² and Q is N. In some embodiments, L is -CR ⁸ -CR ⁹ -CR ¹⁰ -, Y is QR ¹ R ² , Q is N, R ¹ is R ^1A and R ² is R ^2A . In some embodiments, L is -CR ⁵ -. In some embodiments, L is -CR ⁶ -CR ⁷ -. In some embodiments, L is -CR ^N3 -NR ^G -CR ^N4 -. In some embodiments, L is -CR ^N3 -NR ^G -CR ^N4 - wherein R ^G is methyl. In some embodiments, L is -CR ^O1 -O-CR ^O2 -. The groups R ¹ , R ² and R ⁴ ; and R ^1A , R ^2A and R ^4A In some embodiments, R ¹ is R ^1A , and R ^1A is selected from H; linear or branched unsubstituted C _1-12 aliphatic groups; C ₆ aryl, optionally substituted with one or more groups R ^A ; 5-6 membered heteroaryl, optionally substituted with one or more groups R ^B ; C _6-20 aralkyl, optionally substituted with one or more groups R ^C ; and Si(C _1-6 alkyl) ₃ . In some embodiments, R ^1A is H. Hence in some embodiments, the group Y is QHR ² . In some embodiments, R ^1A is selected from linear or branched unsubstituted C _1-12 aliphatic groups. In some embodiments, R ^1A is selected from linear or branched unsubstituted C _1-4 aliphatic groups. In some embodiments, R ^1A is selected from methyl and ethyl. In some embodiments, R ² is R ^2A , and R ^2A is selected from H; linear or branched unsubstituted C _1-12 aliphatic groups; C ₆ aryl, optionally substituted with one or more groups R ^A ; 5-6 membered heteroaryl, optionally substituted with one or more groups R ^B ; C _6-20 aralkyl, optionally substituted with one or more groups R ^C ; and Si(C _1-6 alkyl) ₃ . In some embodiments, R ^2A is selected from C ₆ aryl, optionally substituted with one or more groups R ^A ; and 5-6 membered heteroaryl, optionally substituted with one or more groups R ^B . In some embodiments, R ^2A is phenyl optionally substituted with one or more groups R ^A . In some embodiments, R ^2A is phenyl optionally substituted with one or two groups R ^A . In some embodiments, R ^2A is phenyl substituted with one or more groups R ^A . In some embodiments, R ^2A is phenyl substituted with one or two groups R ^A . In some embodiments, R ^2A is unsubstituted phenyl. In some embodiments, R ^2A is Si(C _1-6 alkyl) ₃ . In some embodiments, R ^2A is Si(C _1-4 alkyl) ₃ . In some embodiments, R ^2A is Si(Me) ₃ . In some embodiments, R ^1A is H and R ^2A is selected from H; linear or branched unsubstituted C _1-12 aliphatic groups; C ₆ aryl, optionally substituted with one or more groups R ^A ; 5-6 membered heteroaryl, optionally substituted with one or more groups R ^B ; C _6-20 aralkyl, optionally substituted with one or more groups R ^C ; and Si(C _1-6 alkyl) ₃ . In some embodiments, R ^1A is H and R ^2A is selected from linear or branched unsubstituted C _1-12 aliphatic groups; C ₆ aryl, optionally substituted with one or more groups R ^A ; 5-6 membered heteroaryl, optionally substituted with one or more groups R ^B ; C _6-20 aralkyl, optionally substituted with one or more groups R ^C ; and Si(C _1-6 alkyl) ₃ . In some embodiments, R ^1A is H and R ^2A is selected from C ₆ aryl, optionally substituted with one or more groups R ^A ; and 5-6 membered heteroaryl, optionally substituted with one or more groups R ^B . In some embodiments, R ^1A is H and R ^2A is phenyl optionally substituted with one or more groups R ^A . In some embodiments, R ^1A is H and R ^2A is phenyl optionally substituted with one or two groups R ^A . In some embodiments, R ^1A is H and R ^2A is phenyl substituted with one or more groups R ^A . In some embodiments, R ^1A is H and R ^2A is phenyl substituted with one or two groups R ^A In some embodiments, R ^1A is H and R ^2A is unsubstituted phenyl. Hence in some embodiments, the group Y is QH(Ph). In some embodiments, when Y is QR ¹ R ² , R ¹ and R ² together with the Q moiety to which they are attached are joined to form a 3-6 membered heterocyclic group optionally substituted with one or more groups R ^E . In some embodiments, R ¹ and R ² together with the Q moiety to which they are attached are joined to form a 3-6 membered unsubstituted heterocyclic group. In some embodiments, R ¹ and R ² together with the Q moiety to which they are attached are joined to form a 5-6 membered heterocyclic group optionally substituted with one or more groups R ^E . In some embodiments, R ¹ and R ² together with the Q moiety to which they are attached are joined to form a 5-6 membered unsubstituted heterocyclic group. In some embodiments, R ¹ and R ² together with the Q moiety to which they are attached are joined to form a 3-6 membered heterocyclic group optionally substituted with one or more groups R ^E . In some embodiments, R ¹ and R ² together with the Q moiety to which they are attached are joined to form a 3-6 membered heteroaromatic group optionally substituted with one or more groups R ^E . In some embodiments, Q is N, and R ¹ and R ² together with the N to which they are attached are joined to form a heterocyclic group selected from: aziridinyl, diaziridinyl, azetidinyl, diazetidinyl, pyrrolidinyl, pyrrolyl, oxazolidinyl, imidazolidinyl, pyrazolidinyl, imidazolyl, pyrazolyl, triazolyl, piperidinyl, diazinanyl, morpholinyl, thiomorpholinyl, thiazinyl and triazinanyl; optionally substituted with one or more groups R ^E . In some embodiments, Q is N, and R ¹ and R ² together with the N to which they are attached are joined to form an unsubstituted heterocyclic group selected from: aziridinyl, diaziridinyl, azetidinyl, diazetidinyl, pyrrolidinyl, pyrrolyl, oxazolidinyl, imidazolidinyl, pyrazolidinyl, imidazolyl, pyrazolyl, triazolyl, piperidinyl, diazinanyl, morpholinyl, thiomorpholinyl, thiazinyl and triazinanyl. In some embodiments, R ⁴ is R ^4A , and R ^4A is selected from H; linear or branched unsubstituted C _1-4 aliphatic groups; C aryl optionally substituted with one or more groups R ^A ; and C _5-6 heteroaryl, optionally substituted with one or more groups R ^B . In some embodiments, R ⁴ is R ^4A , and R ^4A is selected from linear or branched unsubstituted C _1-4 aliphatic groups; C _5-6 aryl, optionally substituted with one or more groups R ^A ; and C _5-6 heteroaryl, optionally substituted with one or more groups R ^B . In some embodiments, R ^4A is independently selected from phenyl optionally substituted with one or more groups R ^A . In some embodiments, R ^4A is independently selected from phenyl substituted with one or more groups R ^A . In some embodiments, R ^4A is independently selected from phenyl substituted with one or two groups R ^A . In some embodiments, R ^4A is independently selected from phenyl substituted with two groups R ^A . In some embodiments, R ^4A is independently selected from phenyl substituted in both ortho- positions with a group R ^A . In some embodiments, R ^4A is independently selected from phenyl substituted in both ortho-positions with a group R ^A and unsubstituted in the meta and para positions. In some embodiments, R ^4A is independently selected from methyl, ethyl and mesityl. In some embodiments, R ¹ and R ² are each independently selected from H; linear or branched unsubstituted C _1-12 aliphatic groups; C ₆ aryl, optionally substituted with one or more groups R ^A ; 5-6 membered heteroaryl, optionally substituted with one or more groups R ^B ; C _6-20 aralkyl, optionally substituted with one or more groups R ^C ; and Si(C _1-6 alkyl) ₃ ; or R ¹ and R ² together with the Q moiety to which they are attached are joined to form a 3-6 membered heterocyclic group optionally substituted with one or more groups R ^E ; and R ⁴ is independently selected from linear or branched unsubstituted C _1-4 aliphatic groups; C ₆ aryl, optionally substituted with one or more groups R ^A ; and 5-6 membered heteroaryl, optionally substituted with one or more groups R ^B . In some embodiments, R ¹ and R ² are each independently selected from H; linear or branched unsubstituted C _1-12 aliphatic groups; C ₆ aryl, optionally substituted with one or more groups R ^A ; 5-6 membered heteroaryl, optionally substituted with one or more groups R ^B ; C _6-20 aralkyl, optionally substituted with one or more groups R ^C ; and Si(C _1-6 alkyl) ₃ ; and R ⁴ is independently selected from linear or branched unsubstituted C _1-4 aliphatic groups; C ₆ aryl, optionally substituted with one or more groups R ^A ; and 5-6 membered heteroaryl, optionally substituted with one or more groups R ^B . In some embodiments, R ¹ is H and R ² is selected from H; linear or branched unsubstituted C _1-12 aliphatic groups; C ₆ aryl, optionally substituted with one or more groups R ^A ; 5-6 membered heteroaryl, optionally substituted with one or more groups R ^B ; C _6-20 aralkyl, optionally substituted with one or more groups R ^C ; and Si(C _1-6 alkyl) ₃ ; and R ⁴ is independently selected from linear or branched unsubstituted C _1-4 aliphatic groups; C ₆ aryl, optionally substituted with one or more groups R ^A ; and 5-6 membered heteroaryl, optionally substituted with one or more groups R ^B . In some embodiments, R ¹ and R ² together with the Q moiety to which they are attached are joined to form a 3-6 membered heterocyclic group optionally substituted with one or more groups R ^E ; and R ⁴ is independently selected from linear or branched unsubstituted C _1-4 aliphatic groups; C ₆ aryl, optionally substituted with one or more groups R ^A ; and 5-6 membered heteroaryl, optionally substituted with one or more groups R ^B . In some embodiments, R ¹ is selected from H; linear or branched unsubstituted C _1-12 aliphatic groups; C ₆ aryl, optionally substituted with one or more groups R ^A ; 5-6 membered heteroaryl, optionally substituted with one or more groups R ^B ; C _6-20 aralkyl, optionally substituted with one or more groups R ^C ; and Si(C _1-6 alkyl) ₃ ; and R ² , R ⁴ and the atoms to which they are attached form a 5-8 membered heterocyclic group, optionally substituted with one or more groups R ^D , and optionally being fused to one or more optionally substituted aryl groups. In some embodiments, R ¹ is H; and R ² , R ⁴ and the atoms to which they are attached form a 5-8 membered heterocyclic group, optionally substituted with one or more groups R ^D , and optionally being fused to one or more optionally substituted aryl groups. When R ² , R ⁴ and the atoms to which they are attached form a 5-8 membered heterocyclic group, said 5-8 membered heterocyclic group is optionally fused to one or more optionally substituted aryl groups. The one or more aryl groups may be unsubstituted. In some embodiments said 5-8 membered heterocyclic group is fused to two optionally substituted aryl groups. The term “fused” here means that the 5-8 membered heterocyclic group shares two atoms with an adjacent ring structure, such that the 5-8 membered heterocyclic group and that adjacent ring form a bicyclic system (or a tricyclic system where two fused aryl groups are present). The group R ³ R ³ is selected from H; linear or branched unsubstituted C _1-12 aliphatic groups; C ₆ aryl, optionally substituted with one or more groups R ^A , and 5-6 membered heteroaryl, optionally substituted with one or more groups R ^B . In some embodiments, R ³ is selected from H; linear or branched unsubstituted C _1-4 aliphatic groups; C ₆ aryl, optionally substituted with one or more groups R ^A , and 5-6 membered heteroaryl, optionally substituted with one or more groups R ^B . In some embodiments, R ³ is selected from linear or branched unsubstituted C _1-4 aliphatic groups; C ₆ aryl, optionally substituted with one or more groups R ^A , and 5-6 membered heteroaryl, optionally substituted with one or more groups R ^B . In some embodiments R ³ is selected from C ₆ aryl, optionally substituted with one or more groups R ^A , and 5-6 membered heteroaryl, optionally substituted with one or more groups R ^B . In some embodiments, R ³ is phenyl, optionally substituted with one or more groups R ^A . In some embodiments, R ³ is independently selected from phenyl optionally substituted with one or more groups R ^A . In some embodiments, R ³ is independently selected from phenyl substituted with one or more groups R ^A . In some embodiments, R ³ is independently selected from phenyl substituted with one or two groups R ^A . In some embodiments, R ³ is independently selected from phenyl substituted with two groups R ^A . In some embodiments, R ³ is independently selected from phenyl substituted in both ortho- positions with a group R ^A . In some embodiments, R ³ is independently selected from phenyl substituted in both ortho-positions with a group R ^A and unsubstituted in the meta and para positions. In some embodiments, R ³ is independently selected from methyl, ethyl and mesityl. In some embodiments, R ³ and R ⁴ are the same, each being selected from any of the groups set out above. In some embodiments, R ³ and R ⁴ are each independently selected from phenyl optionally substituted with one or more groups R ^A . In some embodiments, R ³ and R ⁴ are each independently selected from phenyl substituted in both ortho-positions with a group R ^A . In some embodiments, R ³ and R ⁴ are each independently selected from methyl, ethyl and mesityl. The group R ⁵ In some embodiments, L is -CR ⁵ -, wherein R ⁵ is selected from H, linear or branched unsubstituted C _1-12 aliphatic groups, C _5-6 unsubstituted aryl or heteroaryl groups, and -NR ^N1 R ^N2 . In some embodiments, R ⁵ is selected from H, linear or branched unsubstituted C _1-4 aliphatic groups C _5-6 unsubstituted aryl or heteroaryl groups, and -NR ^N1 R ^N2 . In some embodiments, R ⁵ is H. In some embodiments, R ⁵ is selected from linear or branched unsubstituted C _1-4 aliphatic groups. In some embodiments, R ⁵ is methyl or ethyl. In some embodiments, R ⁵ is methyl. The groups R ⁶ and R ⁷ R ⁶ and R ⁷ are each independently selected from H, linear or branched unsubstituted C _1-12 aliphatic groups, C _5-6 unsubstituted aryl or heteroaryl groups, and -NR ^N1 R ^N2 . In some embodiments, R ⁶ and R ⁷ are each independently selected from H, linear or branched unsubstituted C _1-4 aliphatic groups, C _5-6 unsubstituted aryl or heteroaryl groups, and -NR ^N1 R ^N2 . When L is -CR ⁶ -CR ⁷ -, the ring system containing Zn and L is 5-membered. The skilled person will appreciate that complexes according to formula (I) containing such a 5- membered ring system may carry a charge or a radical. In embodiments where the compound according to formula (I) carries an overall charge, a counterion may be present to balance that charge. For example, where the compound carries an overall single negative charge and exists as an anion, a counter ion [M’’] ⁺ may be present to balance that charge. [M’’] ⁺ may be any suitable cation, for example a metal ion, such as an alkali metal ion. The groups R ^N3 , R ^N4 , R ^O1 and R ^O2 R ^N3 , R ^N4 , R ^O1 and R ^O2 are each independently selected from H, linear or branched unsubstituted C _1-12 aliphatic groups, C _5-6 unsubstituted aryl or heteroaryl groups, and -NR ^N1 R ^N2 . In some embodiments R ^N3 R ^N4 R ^O1 and R ^O2 are each independently selected from H, linear or branched unsubstituted C _1-4 aliphatic groups, C _5-6 unsubstituted aryl or heteroaryl groups, and -NR ^N1 R ^N2 . In some embodiments, R ^N3 , R ^N4 , R ^O1 and R ^O2 are each independently selected from H, and linear or branched unsubstituted C _1-4 aliphatic groups. The groups R ⁸ , R ⁹ and R ¹⁰ In some embodiments, L is -CR ⁸ -CR ⁹ -CR ¹⁰ -, and R ⁸ , R ⁹ and R ¹⁰ are each independently selected from H, linear or branched unsubstituted C _1-12 aliphatic groups, C _5-6 unsubstituted aryl or heteroaryl groups, and -NR ^N1 R ^N2 ; or two or more of R ⁸ , R ⁹ and R ¹⁰ , together with the atoms to which they are attached, are joined to form a monocyclic or bicyclic group, with any remaining groups of R ⁸ , R ⁹ and R ¹⁰ being selected from H, linear or branched unsubstituted C _1-4 aliphatic groups, C _5-6 unsubstituted aryl or heteroaryl groups, and -NR ^N1 R ^N2 . Thus in some embodiments, the compound is a compound according to formula (IA): (IA) or a salt, solvate or hydrate thereof; wherein Y, R ³ , R ⁴ , R ⁸ , R ⁹ and R ¹⁰ are as defined above. In some embodiments of formula (IA), R ⁸ , R ⁹ and R ¹⁰ are each independently selected from H, linear or branched unsubstituted C _1-4 aliphatic groups, C _5-6 unsubstituted aryl or heteroaryl groups, and NR ^N1 R ^N2 In some embodiments of formula (IA), R ⁸ , R ⁹ and R ¹⁰ are each independently selected from H, and linear or branched unsubstituted C _1-4 aliphatic groups. In some embodiments of formula (IA), R ⁸ , R ⁹ and R ¹⁰ are each independently selected from H and methyl. In some embodiments of formula (IA), R ⁸ , R ⁹ and R ¹⁰ are each independently selected from H and methyl; and Y is QR ¹ R ² . In some embodiments of formula (IA), R ⁹ is H. In some embodiments of formula (IA), one or both of R ⁸ and R ¹⁰ is linear or branched unsubstituted C _1-4 aliphatic groups. In some embodiments of formula (IA), one or both of R ⁸ and R ¹⁰ is linear unsubstituted C _1-4 aliphatic groups. In some embodiments of formula (IA), one or both of R ⁸ and R ¹⁰ is methyl. In some embodiments of formula (IA), R ⁹ is H and one or both of R ⁸ and R ¹⁰ is a linear or branched unsubstituted C _1-4 aliphatic group. In some embodiments of formula (IA), R ⁹ is H and one or both of R ⁸ and R ¹⁰ is methyl. In some embodiments of formula (IA), R ⁹ is H and both of R ⁸ and R ¹⁰ are methyl. In some embodiments of formula (IA), two or more of R ⁸ , R ⁹ and R ¹⁰ , together with the atoms to which they are attached, are joined to form a monocyclic or bicyclic group, with any remaining groups of R ⁸ , R ⁹ and R ¹⁰ being selected from H, linear or branched unsubstituted C _1-4 aliphatic groups, C _5-6 unsubstituted aryl or heteroaryl groups, and -NR ^N1 R ^N2 . In some embodiments of formula (IA), R ⁸ and R ⁹ , together with the atoms to which they are attached, are joined to form a monocyclic group, and R ¹⁰ is selected from H, linear or branched unsubstituted C _1-4 aliphatic groups, C _5-6 unsubstituted aryl or heteroaryl groups, and -NR ^N1 R ^N2 . In some embodiments of formula (IA), R ⁸ and R ⁹ , together with the atoms to which they are attached, are joined to form a 6-membered monocyclic group, and R ¹⁰ is selected from H, linear or branched unsubstituted C _1-4 aliphatic groups, C _5-6 unsubstituted aryl or heteroaryl groups, and -NR ^N1 R ^N2 . In some embodiments of formula (IA), R ⁸ and R ⁹ , together with the atoms to which they are attached, are joined to form a 6-membered monocyclic group, and R ¹⁰ is selected from H, and linear or branched unsubstituted C _1-4 aliphatic groups. In some embodiments of formula (IA), R ⁸ , R ⁹ and R ¹⁰ , together with the atoms to which they are attached, are joined to form a bicyclic group. In some embodiments of formula (IA), R ⁸ , R ⁹ and R ¹⁰ , together with the atoms to which they are attached, are joined to form a naphthyl group. In some embodiments, the compound is a compound according to formula (IB): (IB) or a salt, solvate or hydrate thereof; wherein: Q is selected from N, P and P(=O); R ¹ and R ² are each independently selected from H; linear or branched unsubstituted C _1-12 aliphatic groups; C ₆ aryl, optionally substituted with one or more groups R ^A ; 5-6 membered heteroaryl, optionally substituted with one or more groups R ^B ; C _6-20 aralkyl, optionally substituted with one or more groups R ^C ; and Si(C _1-6 alkyl) ₃ ; R ³ and R ⁴ are each independently selected from H; linear or branched unsubstituted C _1-12 aliphatic groups; C ₆ aryl, optionally substituted with one or more groups R ^A ; and 5-6 membered heteroaryl, optionally substituted with one or more groups R ^B ; R ⁸ , R ⁹ and R ¹⁰ are each independently selected from H, linear or branched unsubstituted C _1-12 aliphatic groups, C _5-6 unsubstituted aryl or heteroaryl groups, and -NR ^N1 R ^N2 ; R ^N1 and R ^N2 are each independently selected from linear or branched unsubstituted C _1-6 aliphatic groups, or R ^N1 and R ^N2 together with the N atom to which they are attached are joined to form a 3-6 membered heterocyclic group optionally substituted with one or more groups R ^E ; and R ^A , R ^B , R ^C and R ^E are each independently selected from linear or branched unsubstituted C _1-6 aliphatic groups. The groups R ^N1 and R ^N2 In some embodiments, R ⁵ is -NR ^N1 R ^N2 . In some embodiments, one or more of R ⁶ and R ⁷ is -NR ^N1 R ^N2 . In some embodiments, one or more of R ⁸ , R ⁹ and R ¹⁰ is -NR ^N1 R ^N2 . R ^N1 and R ^N2 are each independently selected from linear or branched unsubstituted C _1-6 aliphatic groups, or R ^N1 and R ^N2 together with the N atom to which they are attached are joined to form a 3-6 membered heterocyclic group optionally substituted with one or more groups R ^E . In some embodiments, R ^N1 and R ^N2 are each independently selected from linear or branched unsubstituted C _1-6 aliphatic groups. In some embodiments, R ^N1 and R ^N2 are each independently selected from linear or branched unsubstituted C _1-4 aliphatic groups. In some embodiments, R ^N1 and R ^N2 are each independently selected from linear unsubstituted C _1-6 aliphatic groups. In some embodiments, R ^N1 and R ^N2 are each independently selected from linear unsubstituted C _1-4 aliphatic groups. In some embodiments, R ^N1 and R ^N2 are each independently selected from methyl or ethyl. In some embodiments, R ^N1 and R ^N2 together with the N atom to which they are attached are joined to form a 3-6 membered heterocyclic group optionally substituted with one or more groups R ^E . In some embodiments, R ^N1 and R ^N2 together with the N atom to which they are attached are joined to form an unsubstituted 3-6 membered heterocyclic group. In some embodiments, R ^N1 and R ^N2 together with the N atom to which they are attached are joined to form a heterocyclic group selected from: aziridinyl, diaziridinyl, azetidinyl, diazetidinyl, pyrrolidinyl, pyrrolyl, oxazolidinyl, imidazolidinyl, pyrazolidinyl, imidazolyl, pyrazolyl, triazolyl, piperidinyl, diazinanyl, morpholinyl, thiomorpholinyl, thiazinyl and triazinanyl; optionally substituted with one or more groups R ^E . In some embodiments, R ^N1 and R ^N2 together with the N atom to which they are attached are joined to form an unsubstituted heterocyclic group selected from: aziridinyl, diaziridinyl, azetidinyl, diazetidinyl, pyrrolidinyl, pyrrolyl, oxazolidinyl, imidazolidinyl, pyrazolidinyl, imidazolyl, pyrazolyl, triazolyl, piperidinyl, diazinanyl, morpholinyl, thiomorpholinyl, thiazinyl and triazinanyl. The groups R ^A , R ^B , R ^C , R ^D and R ^E R ^A , R ^B , R ^C , R ^D and R ^E are each independently selected from linear or branched unsubstituted C _1-6 aliphatic groups; halo; O(C _1-6 alkyl); -CF ₃ , -CF ₂ H, -CFH ₂ ; -OCF ₃ , -OCF ₂ H and -OCFH ₂ . In some embodiments, R ^A , R ^B , R ^C , R ^D and R ^E are each independently selected from linear or branched unsubstituted C _1-6 aliphatic groups; halo; and O(C _1-6 alkyl). In some embodiments, R ^A , R ^B , R ^C , R ^D and R ^E are each independently selected from linear or branched unsubstituted C _1-6 aliphatic groups; halo; and O(Me). In some embodiments, R ^A , R ^B , R ^C , R ^D and R ^E are each independently selected from linear or branched unsubstituted C _1-6 aliphatic groups; Cl; and O(Me). In some embodiments, R ^A , R ^B , R ^C , R ^D and R ^E are each independently selected from linear or branched unsubstituted C _1-4 aliphatic groups. In some embodiments, R ^A , R ^B , R ^C , R ^D and R ^E are each independently selected from linear unsubstituted C _1-6 aliphatic groups. In some embodiments, R ^A , R ^B , R ^C , R ^D and R ^E are each independently selected from linear unsubstituted C _1-4 aliphatic groups. In some embodiments, R ^A , R ^B , R ^C , R ^D and R ^E are each independently selected from methyl and ethyl. The groups R ^F and R ^G R ^F and R ^G are each independently selected from H; C _1-12 alkyl groups; C ₆ aryl, optionally substituted with one or more groups R ^A ; 5-6 membered heteroaryl, optionally substituted with one or more groups R ^B ; C _6-20 aralkyl, optionally substituted with one or more groups R ^C ; -S(=O) ₂ CF ₃ ; and -C(=O)R ^H , wherein R ^H is linear or branched C _1-6 alkyl optionally substituted with one or more groups independently selected from OH and halo. In some embodiments, R ^F and R ^G are each independently selected from H; C _1-12 alkyl groups; C ₆ aryl, optionally substituted with one or more groups R ^A ; 5-6 membered heteroaryl, optionally substituted with one or more groups R ^B ; and C _6-20 aralkyl, optionally substituted with one or more groups R ^C . In some embodiments, R ^F and R ^G are each independently selected from H; branched C _1-12 alkyl groups; unsubstituted C ₆ aryl; and unsubstituted C _6-20 aralkyl. In some embodiments, Y is OR ^F and R ^F is selected from H; C _1-12 alkyl groups; C ₆ aryl, optionally substituted with one or more groups R ^A ; 5-6 membered heteroaryl, optionally substituted with one or more groups R ^B ; C _6-20 aralkyl, optionally substituted with one or more groups R ^C ; -S(=O)2CF ₃ ; and -C(=O)R ^H , wherein R ^H is linear or branched C _1-6 alkyl optionally substituted with one or more groups independently selected from OH and halo. In some embodiments, R ^F is selected from C _1-12 alkyl groups; C ₆ aryl, optionally substituted with one or more groups R ^A ; 5-6 membered heteroaryl, optionally substituted with one or more groups R ^B ; and C _6-20 aralkyl, optionally substituted with one or more groups R ^C . In some embodiments, R ^F is selected from C _1-12 unsubstituted alkyl groups; C ₆ aryl, optionally substituted with one or more groups R ^A ; and C _6-20 aralkyl, optionally substituted with one or more groups R ^C . In some embodiments, R ^F is C ₆ aryl, optionally substituted with one or more groups R ^A . In some embodiments, R ^F is unsubstituted C ₆ aryl. In some embodiments, the group OR ^F is selected from one of the following groups: and . Provisos The compound according to formula (I) is not a compound according to formula (X): (X) wherein the group XX is selected from -N(SiMe ₃ ) ₂ and -NH(DIPP); and wherein DIPP is the group: In some embodiments, the compound according to formula (I) is not a compound according to formula (X), wherein the group XX is selected from -NR ^1A R ^2A , wherein R ^1A and R ^2A are as defined above. In some embodiments, the compound according to formula (I) is not a compound according to formula (X), wherein the group XX is selected from -QR ¹ R ² , wherein Q, R ¹ and R ² are as defined above. In some embodiments, the compound according to formula (I) is not a compound according to formula (X), wherein the group XX is Y, wherein Y is as defined above. Certain specific compounds according to formula (X) are disclosed by Webb et al. in the article “Utilising an anilido-imino ligand to stabilise zinc-phosphanide complexes: reactivity and fluorescent properties”, Dalton Trans, 2019, 48, 8094. However, this article does not teach or suggest any application of these complexes in the reduction or hydrogenation of compounds containing double or triple bonds, such as alkynes. Further embodiments of formula (I) In some embodiments, the invention provides a compound according to formula (I): 3 (I) or a salt, solvate or hydrate thereof; wherein: Y is selected from -QR ¹ R ² , and OR ^F ; wherein Q is selected from N, P and P(=O); L is selected from -CR ⁸ -CR ⁹ -CR ¹⁰ -, -CR ⁵ -, -CR ⁶ -CR ⁷ -, -CR ^N3 -NR ^G -CR ^N4 - and -CR ^O1 -O-CR ^O2 -; either: (A) R ¹ is R ^1A , R ² is R ^2A and R ⁴ is R ^4A ; or (B) R ⁴ is R ^4A ; and R ¹ and R ² together with the Q moiety to which they are attached are joined to form a 3-6 membered heterocyclic group optionally substituted with one or more groups R ^E ; or (C) R ¹ is R ^1A ; and R ² , R ⁴ and the atoms to which they are attached form a 5-8 membered heterocyclic group, optionally substituted with one or more groups R ^D , and optionally being fused to one or more optionally substituted aryl groups; R ³ is selected from H; linear or branched unsubstituted C _1-12 aliphatic groups; C ₆ aryl, optionally substituted with one or more groups R ^A , and 5-6 membered heteroaryl, optionally substituted with one or more groups R ^B ; R ⁵ , R ⁶ , R ⁷ , R ^N3 , R ^N4 , R ^O1 and R ^O2 are each independently selected from H, linear or branched unsubstituted C _1-12 aliphatic groups, C _5-6 unsubstituted aryl or heteroaryl groups, and -NR ^N1 R ^N2 ; R ⁸ , R ⁹ and R ¹⁰ are each independently selected from H, linear or branched unsubstituted C _1-12 aliphatic groups, C _5-6 unsubstituted aryl or heteroaryl groups, and -NR ^N1 R ^N2 ; R ^1A , R ^2A and R ^4A are each independently selected from H; linear or branched unsubstituted C _1-12 aliphatic groups; C ₆ aryl, optionally substituted with one or more groups R ^A ; 5-6 membered heteroaryl, optionally substituted with one or more groups R ^B ; C _6-20 aralkyl, optionally substituted with one or more groups R ^C ; and Si(C _1-6 alkyl) ₃ ; R ^N1 and R ^N2 are each independently selected from linear or branched unsubstituted C _1-6 aliphatic groups, or R ^N1 and R ^N2 together with the N atom to which they are attached are joined to form a 3-6 membered heterocyclic group optionally substituted with one or more groups R ^E ; R ^A , R ^B , R ^C , R ^D and R ^E are each independently selected from linear or branched unsubstituted C _1-6 aliphatic groups; halo; O(C _1-6 alkyl); -CF ₃ , -CF ₂ H, -CFH ₂ ; -OCF ₃ , -OCF ₂ H and -OCFH ₂ ; R ^F and R ^G are independently selected from H; C _1-12 alkyl groups; C ₆ aryl, optionally substituted with one or more groups R ^A ; 5-6 membered heteroaryl, optionally substituted with one or more groups R ^B ; C _6-20 aralkyl, optionally substituted with one or more groups R ^C ; -S(=O)2CF ₃ ; and -C(=O)R ^H , wherein R ^H is linear or branched C _1-6 alkyl optionally substituted with one or more groups independently selected from OH and halo. In some embodiments, Y is -NR ¹ R ² ; L is -CR ⁸ -CR ⁹ -CR ¹⁰ -; R ¹ is R ^1A , R ² is R ^2A , R ⁴ is R ^4A ; R ³ and R ^4A are each independently selected from H; linear or branched unsubstituted C _1-12 aliphatic groups; C ₆ aryl, optionally substituted with one or more groups R ^A , and 5-6 membered heteroaryl, optionally substituted with one or more groups R ^B ; R ⁸ , R ⁹ and R ¹⁰ are each independently selected from H, linear or branched unsubstituted C _1-12 aliphatic groups, C _5-6 unsubstituted aryl or heteroaryl groups, and -NR ^N1 R ^N2 ; R ^1A and R ^2A are each independently selected from H; linear or branched unsubstituted C _1-12 aliphatic groups; C ₆ aryl, optionally substituted with one or more groups R ^A ; 5-6 membered heteroaryl, optionally substituted with one or more groups R ^B ; C _6-20 aralkyl, optionally substituted with one or more groups R ^C ; and Si(C _1-6 alkyl) ₃ ; and R ^A , R ^B , R ^C , R ^N1 and R ^N2 are as defined under the first aspect. In some embodiments, Y is -NR ¹ R ² ; L is -CR ⁸ -CR ⁹ -CR ¹⁰ -; R ¹ is R ^1A , R ² is R ^2A , R ⁴ is R ^4A ; R ³ and R ^4A are each independently selected from linear or branched unsubstituted C _1-12 aliphatic groups; and C ₆ aryl, optionally substituted with one or more groups R ^A ; R ⁸ , R ⁹ and R ¹⁰ are each independently selected from H, and linear or branched unsubstituted C _1-12 aliphatic groups, R ^1A and R ^2A are each independently selected from H; and C ₆ aryl, optionally substituted with one or more groups R ^A ; and R ^A is as defined under the first aspect. In some embodiments, Y is -NR ¹ R ² ; L is -CR ⁸ -CR ⁹ -CR ¹⁰ -; R ¹ is R ^1A , R ² is R ^2A , R ⁴ is R ^4A ; R ³ and R ^4A are each independently selected from C ₆ aryl, optionally substituted with one or more groups R ^A ; R ⁸ , R ⁹ and R ¹⁰ are each independently selected from H, and linear or branched unsubstituted C _1-6 aliphatic groups, R ^1A and R ^2A are each independently selected from H; and C ₆ aryl, optionally substituted with one or more groups R ^A ; and R ^A is as defined under the first aspect. In some embodiments, the compound is: . A second aspect of the invention is a catalyst comprising a compound according to the first aspect. In some embodiments, the catalyst is a hydrogenation catalyst. In some embodiments, the catalyst is an alkyne hydrogenation catalyst. In some embodiments the catalyst comprises a compound according to the first aspect and a support. The support may be a solid support. The support may comprise a resin material. In some embodiments, the support comprises a functional group attached to the compound of formula (I). In some embodiments, when Y is QR ¹ R ² , the support comprises a functional group attached to the compound of formula (I) via the Q-R ² group. In other words, the group Q ^R2 in the compound according to formula (I) may act as a linker attaching the compound to a support. In some embodiments, the supported form of the compound may have a structure according to formula (XI): *Q(R ¹ )-R ^2X -A (XI) wherein the asterisk (*) represents the point of attachment to the Zn atom of the compound of formula (I); Q and R ¹ are as defined under the first aspect above; R ^2X is a divalent derivative of the R ² group defined above; and A is a support moiety. In some embodiments the support moiety A is a solid support. In some embodiments the support moiety A is a resin. In some embodiments, R ^2X is the group -Ph-O-(CH ₂ ) _n -*, where the asterisk (*) represents the point of attachment to the support A; and wherein Ph is phenylene optionally substituted with one or more unsubstituted straight or branched C _1-6 alkyl groups. A third aspect of the invention is a method of reducing or hydrogenating a double or triple bond in the presence of a catalyst comprising a compound according to the first aspect. In some embodiments, the method is a method of reducing or hydrogenating a compound selected from alkyne, alkene, nitrile, carbonyl (including aldehydes and ketones), ester and amide in the presence of a catalyst comprising a compound according to the first aspect. In some embodiments, the method is a method of semi-hydrogenation of an alkyne to provide an alkene. In some embodiments, the method is a method of manufacturing a compound selected from β-carotene, polyene antifungal drugs, crocaine, polyunsaturated fatty acids (PUFAs), pheromones and cruentaren. In some embodiments, the method is a method of stereoselectively reducing or hydrogenating the double or triple bond to provide an excess of one stereoisomer. In some embodiments, the molar ratio of a first stereoisomer to a second stereoisomer is at least 55:45, for example at least 60:40, at least 70:30, at least 80:20, at least 90:10, at least 95:5 or at least 99:1. In some embodiments the first stereoisomer is a (Z)-alkene and the second stereoisomer is an (E)-alkene. In some embodiments, the method is a method of chemoselectively reducing or hydrogenating the double or triple bond. In some embodiments, the molar ratio of a first product to a second product is at least 2:1, for example at least 5:1, at least 10:1, at least 20:1, at least 30:1, at least 50:1 or at least 99:1. In some embodiments the first product is an alkene and the second product is an alkane which results from further hydrogenation of the alkene. In some embodiments, the method comprises reacting an alkyne according to formula (V): (V) with dihydrogen (H ₂ ), in the presence of a catalyst comprising a compound according to the first aspect. In some embodiments, the method comprises reacting an alkyne according to formula (V): (V) with dihydrogen (H ₂ ), in the presence of a catalyst comprising a compound according to the first aspect, to produce an alkene according to formula (VI): (VI). The catalyst facilitates the chemo- and stereo-selective production of the alkene according to formula (VI). In other words, semi-hydrogenation takes place with very little over- hydrogenation, producing preferentially the alkene (VI) with little or no overhydrogenation to the alkane (chemoselectivity), and the reaction preferentially produces the (Z)-alkene over the (E)-alkene (stereoselectivity). In some embodiments the method of the third aspect comprises reducing or hydrogenating a double or triple bond in the presence of a catalyst comprising a supported catalyst with a structure according to formula (XI) described above. In such embodiments the method may be a flow process in which the supported catalyst forms part of a stationary phase, for example immobilised on a resin within a column. Reactants including hydrogen and a compound containing a double or triple bond (e.g. an alkyne) may then be contacted with the supported catalyst, for example through passing them through the column. The skilled person is aware of suitable reaction conditions for carrying out catalytic hydrogenation reactions. In some embodiments, the hydrogenation comprises first dissolving the catalyst comprising the compound according to formula (I) in a suitable solvent (Solvent A) to form a catalyst solution (Solution A), and combining Solution A with the compound to be hydrogenated, e.g. the alkyne according to formula (V). Solvent A may be an organic solvent, for example toluene. The compound to be hydrogenated may also be dissolved in a solvent (Solvent B) to form a solution (Solution B) before combining with Solution A. Solvent A and Solvent B may be the same solvent In some embodiments both Solvent A and Solvent B are toluene After mixing Solution A with Solution B to form the reaction mixture, the reaction mixture may be pressurised with hydrogen and heated up to the reaction temperature. Hydrogenation may be performed under a hydrogen pressure of from 100 kPa to 10 MPa, for example from 200 kPa to 8 MPa, 500 kPa to 5 MPa, 1 MPa to 5 MPa or 800 kPa to 2.5 MPa. Hydrogenation may be performed at a temperature of from 50 °C to 200 °C, for example from 60 °C to 180 °C, from 80 °C to 160 °C or from 100 °C to 150 °C. In some embodiments, the reaction mixture is stirred during the hydrogenation. The reaction time may be from 1 h to 50 h, for example from 1 h to 50 h, from 2 h to 40 h, from 5 h to 30 h, from 5 h to 20 h, from 10 h to 20 h or from 12 h to 18 h. In some embodiments, R ¹¹ and R ¹² are each independently selected from alkyl and aryl groups. In some embodiments, R ¹¹ and R ¹² are each independently selected from linear or branched unsubstituted C _1-6 alkyl, and C _3-8 aromatic or heteroaromatic groups. However, the skilled person will understand that the hydrogenation may be carried out on any alkyne regardless of the identity of the groups R ¹¹ and R ¹² . A fourth aspect is a method of activating dihydrogen for hydrogenation, comprising reacting dihydrogen with a catalyst comprising a compound according to the first aspect. The inventors have found that compounds of formula (I) according to the invention provide for dihydrogen activation at zinc. The thus activated dihydrogen may then react with a reducible double or triple bond, such as an alkyne, in a hydrogenation reaction. This has been confirmed by DFT studies into the dihydrogen activation process for Compound 1: Compound 1 as explained in more detail in the appended examples. A fifth aspect is a compound according to formula (VII): (VII) wherein L, R ³ , R ⁴ , R ¹¹ and R ¹² are as defined above. The inventors have determined that the zinc vinyl compound according to formula (VII) is formed as a key intermediate in the alkyne semi-hydrogenation reaction when an alkyne according to formula (V) is hydrogenated in the presence of a catalyst comprising a compound according to formula (I). This was confirmed by NMR characterisation of the intermediate of formula (VII). Without wishing to be bound by theory, and using Compound 1 below as a specific example, the inventors believe that the catalytic hydrogenation of the alkyne proceeds according to the mechanism shown in Scheme A below: Compound 1 Scheme A where the numbers indicate DFT calculated barriers and thermodynamics for R = Ph (kcal mol ^-1 ). Thus a sixth aspect of the invention is a method of preparing an intermediate according to formula (VII): (VII) the method comprising reacting an alkyne according to formula (V): (V) with dihydrogen (H ₂ ) in the presence of a catalyst comprising a compound according to formula (I): 3 (I) or a salt, solvate or hydrate thereof; wherein L, Y, R ³ , R ⁴ , R ¹¹ and R ¹² are as defined above. Protonation of the intermediate according to formula (VII) then provides the hydrogenated alkene product and the compound according to formula (I) may be regenerated. A seventh aspect of the invention is therefore a method of preparing an alkene according to formula (VI): (VI) the method comprising protonating a compound according to formula (VII): (VII) wherein L, R ³ , R ⁴ , R ¹¹ and R ¹² are as defined above. The protonation may be performed by any suitable acid, but preferably the protonation is performed by the species HY (e.g. HQR ¹ R ² ) which is generated when the compound according to formula (I) is reacted with dihydrogen and therefore may be present in the reaction mixture. In this way, the compound according to formula (I) is regenerated by the reaction with HY (e.g. HQR ¹ R ² ) such that it may act as a catalyst for the process. An eighth aspect of the invention is a method of making a compound according to formula (I): (I) from starting materials comprising a compound according to formula (II): (II) wherein Y, L, R ³ and R ⁴ are as defined in the first aspect above. For the avoidance of doubt, all the options and preferences expressed above for all variables within the formula (I) apply equally to those same variables where they appear in other formulae herein (including, for example, formula (II)). In some embodiments, the method of the eighth aspect comprises (a) reacting the compound according to formula (II) with a first metal-containing reagent to form a compound according to formula (III):

(III) wherein M is a metal atom selected from Li, Na and K; (b) reacting the compound according to formula (III) with a zinc salt ZnX ₂ to form a compound according to formula (IV): (IV) wherein X is a monovalent anion; and (c) converting the compound according to formula (IV) into the compound according to formula (I). In some embodiments, step (c) comprises reacting the compound according to formula (IV) with M’Y to form the compound according to formula (I), wherein M’ is a metal atom and Y is as defined under the first aspect. M’ may be selected from Li, Na and K. In some embodiments, step (c) comprises reacting the compound according to formula (IV) with MgYX’ to form the compound according to formula (I), wherein X’ is a monovalent anion and Y is as defined under the first aspect. In some embodiments, X’ is a halogen anion. In some embodiments, X’ is Cl. In some embodiments, step (c) comprises reacting the compound according to formula (IV) with a Grignard reagent and HY to form the compound according to formula (I), wherein Y is as defined under the first aspect The skilled person is aware of suitable Grignard reagents but non-limiting examples are reagents of the formula R ¹³ MgX’’, wherein R ¹³ is selected from aliphatic and aryl groups (for example, C _1-20 alkyl, aryl or vinyl) and X’’ is a monovalent anion, for example Cl. In some embodiments, M is Li. In some embodiments, the first metal-containing reagent is a lithiating reagent. In some embodiments, the first metal-containing reagent is an organolithium reagent. In some embodiments, the first metal-containing reagent is n-BuLi. In some embodiments, M is Na. In some embodiments, the first metal-containing reagent is selected from NaH and NaOR ^Na , wherein R ^Na is an alkyl group. In some embodiments, M is K. In some embodiments, the first metal-containing reagent is selected from KH and KOR ^K , wherein R ^K is an alkyl group. In some embodiments, M’ is Li. In some embodiments, M’ is Na. In some embodiments, M’ is K. In some embodiments, M’Y is made by reacting a second metal-containing reagent with HY. In some embodiments, M’ is Li and the second metal-containing reagent is a lithiating reagent. In some embodiments, M’ is Li and the second metal-containing reagent is an organolithium reagent. In some embodiments, M’ is Li and the second metal-containing reagent is n-BuLi. In some embodiments, M’ is Na and the second metal-containing reagent is selected from NaH and NaOR ^Na , wherein R ^Na is an alkyl group. In some embodiments, M’ is K and the second metal-containing reagent is selected from KH and KOR ^K , wherein R ^K is an alkyl group. In some embodiments, both of the first organolithium reagent and the second metal- containing reagent comprises ⁿ BuLi. In some embodiments, the method of the eighth aspect comprises, in step (a), dissolving the compound according to formula (II) in a solvent (Solvent C) to form a solution (Solution C), then adding the first metal-containing reagent to Solvent C. The first metal-containing reagent may be added drop-wise to Solution C. In some embodiments, Solvent C is an organic solvent, e.g. tetrahydrofuran (THF). In some embodiments the addition of the first metal-containing reagent to Solvent C is performed at low temperature, e.g. below -70 °C. The reaction mixture may then be allowed to warm, for example to around room temperature. In some embodiments the reaction mixture is stirred after warming. The stirring may be performed for at least 1 h, for example at least 5 h, at least 8 h or at least 10 h. Step (b) of the method according to the eighth aspect may include dissolving ZnX ₂ in a solvent (Solvent D) to form a solution (Solution D). In some embodiments, Solvent D is the same solvent as Solvent C. In some embodiments, Solvent D is an organic solvent, e.g. tetrahydrofuran (THF). The solution from step (a) containing the compound according to formula (III) may then be added to Solution D. In some embodiments, it is added dropwise to Solution D. In some embodiments the addition to Solvent D is performed at low temperature, e.g. below -70 °C. The reaction mixture may then be allowed to warm, for example to around room temperature. In some embodiments the reaction mixture is stirred after warming. The stirring may be performed for at least 1 h, for example at least 5 h, at least 8 h or at least 10 h. Step (c) of the method according to the eighth aspect may comprise first forming the compound M’Y by reacting a second metal-containing reagent with YH. In some embodiments, this comprises adding the second metal-containing reagent to a solution of YH. The addition may be dropwise addition of the second metal-containing reagent. In some embodiments the addition is performed at low temperature, e.g. below -70 °C. The solution of YH may be a solution in organic solvent, e.g. THF. The reaction mixture may then be allowed to warm, for example to around room temperature. In some embodiments the reaction mixture is stirred after warming. The stirring may be performed for at least 1 h, for example at least 5 h, at least 8 h or at least 10 h. The compound M’Y may then be added to the compound according to formula (IV) to complete step (c) of the method. This addition may be performed at a temperature of from 5 °C to 40 °C, for example from 10 °C to 30 °C, from 15 °C to 30 °C, 20 °C to 30 °C, or at about room temperature. In some embodiments the reaction mixture is stirred after the addition. The stirring may be performed for at least 1 h, for example at least 5 h, at least 8 h or at least 10 h. Optional purification steps may then be performed, including for example one or more recrystallisation and/or washing steps. The product may then be dried, for example by drying under vacuum. A ninth aspect of the invention is an intermediate according to formula (IV): (IV) wherein L, R ³ and R ⁴ are as defined in the first aspect and X is a monovalent anion. In some embodiments, X is Cl. A tenth aspect of the invention is a method of making an intermediate according to formula (IV): (IV) comprising reacting a compound according to formula (III) with ZnX ₂

(III) wherein L, R ³ and R ⁴ are as defined in the first aspect, M is a metal atom selected from Li, Na and K, and X is as defined under the ninth aspect. In some embodiments, M is Li. An eleventh aspect of the invention is a method of making a compound according to formula (I): (I) from a compound according to formula (IV): (IV) wherein Y, L, R ³ and R ⁴ are as defined in the first aspect, and X is a monovalent anion. In some embodiments, the method of the eleventh aspect comprises reacting the compound according to formula (IV) with M’Y to form the compound according to formula (I), wherein M’ is a metal atom and Y is as defined under the first aspect. M’ may be selected from Li, Na and K. In some embodiments, the method of the eleventh aspect comprises reacting the compound according to formula (IV) with MgYX’ to form the compound according to formula (I), wherein X’ is a monovalent anion and Y is as defined under the first aspect. In some embodiments, X and X’ are each independently selected from halogens and monovalent organic anions. In some embodiments, X and X’ are each independently selected from halogens, -OAc, -OTf and -OC(=O)CF ₃ . In some embodiments, X and X’ are each independently selected from halogens. In some embodiments, X is Cl. In some embodiments, X’ is Cl. In some embodiments, M’ is Li. In some embodiments, the method of the eleventh aspect comprises reacting the compound according to formula (IV) with a Grignard reagent and HY to form the compound according to formula (I), wherein Y is as defined under the first aspect. The skilled person is aware of suitable Grignard reagents, but non-limiting examples are reagents of the formula R ¹³ MgX’’, wherein R ¹³ is selected from aliphatic and aryl groups (for example, C1-20alkyl, aryl or vinyl) and X’’ is a monovalent anion, for example Cl. A twelfth aspect of the invention is a method of making a compound according to formula (VIII): (VIII) comprising reacting a compound according to formula (I): 3 (I) with dihydrogen (H ₂ ), wherein L, Y, R ³ and R ⁴ are as defined under the first aspect. A thirteenth aspect of the invention is the use of a compound according to the first aspect or catalyst according to the second aspect in a hydrogenation process, for example an alkyne hydrogenation process. Another aspect us the use of a compound according to the first aspect as a catalyst a hydrogenation process, for example an alkyne hydrogenation process. General synthetic methods A number of synthetic routes are available for the preparation of compounds according to the invention. The skilled person will be able to select a suitable synthetic route based on the particular target compound. In some embodiments, synthesis may involve a stepwise reaction starting from a proligand compound (II), as shown in Scheme 1 below.

Scheme 1 In the reaction according to Scheme 1, pro-ligand compound of formula (II) is first reacted with a metal salt comprising a metal ion M ⁺ , to form the derivative according to formula (III). The metal ion M ⁺ may be any suitable ion including Li, Na or K. The metal salt which provides the ion M ⁺ may be, for example, a lithiating agent, such as an organolithium reagent, e.g. nBuLi. Alternatively, the salt may be NaH, NaOR, KH or KOR (wherein R is alkyl). The derivative according to formula (III) is then reacted with zinc salt ZnX ₂ , where X is any suitable monovalent anion. For example, X may be Cl, triflate or a carbanion such as an alkyl anion. Reacting the derivative according to formula (III) with ZnX ₂ provides the complex according to formula (IV). Finally, the complex according to formula (IV) is reacted with M’-Y (for example, M’-QR ¹ R ² ) to form the compound according to formula (I). In the compound M’-Y, M’ is a metal atom such as Li, Na or K. M’-Y may be formed by the reaction of HY with a suitable reagent for introducing the metal atom, such as a lithiating reagent e.g. nBuLi. As an alternative in step (c), a Grignard reagent MgYX’ may be reacted with the compound according to formula (IV) where X’ is a halogen for example Cl An alternative method of synthesis for the compounds according to formula (I) involves the direct reaction of the proligand compound with a suitable zinc salt, as shown in Scheme 2 below. Scheme 2 In the reaction according to Scheme 2, pro-ligand compound of formula (II) is first reacted with zinc salt ZnX ₂ , where X is any suitable monovalent anion. For example, X may be Cl, triflate or a carbanion such as an alkyl anion. Reacting the proligand according to formula (II) with ZnX ₂ provides the complex according to formula (IV). Finally, the complex according to formula (IV) is reacted with M’-Y to form the compound according to formula (I). In the compound M’-Y, M’ is a metal atom such as Li, Na or K. M’- QR ¹ R ² may be formed by the reaction of HY with a suitable reagent for introducing the metal atom, such as a lithiating reagent e.g. nBuLi. As an alternative in step (e), a Grignard reagent MgYX’ may be reacted with the compound according to formula (IV), where X’ is a halogen, for example Cl. In an alternative synthesis, step (e) may involve the reaction of the compound according to formula (IV) with a Grignard reagent R ¹³ MgX’’, wherein R ¹³ is selected from aliphatic and aryl groups (for example, C1- 20alkyl, aryl or vinyl) and X’’ is a monovalent anion, for example Cl. Reaction with HY then gives the compound according to formula (I). The order of addition of R ¹³ MgX’’ and HY may not be critical. An alternative method of synthesis for the compounds according to formula (I) involves the reaction of a zinc compound Zn(Y) ₂ with the proligand compound as shown in Scheme 3 below. Scheme 3 3 An alternative method of synthesis for the compounds according to formula (I) involves the reaction of a zinc hydride complex of formula (VIII) with HY as shown in Scheme 4 below. Scheme 4 Specific compound synthesis In the following examples, all manipulations were carried out under standard Schlenk-line and glovebox techniques under an inert atmosphere of argon or dinitrogen. An MBraun Labmaster glovebox was employed operating at <0.1 ppm O2 and <0.1 ppm H ₂ O. NMR scale reactions were performed in J. Young tap NMR tubes equipped with internal standard capillaries of ferrocene or bis(trimethylsilyl)methane in C ₆ D ₆ and were prepared in a glovebox. Solvents were dried over activated alumina from an SPS (solvent purification system) based upon the Grubbs design and degassed before use. Glassware was dried for 12 hours at 120 °C prior to use. Benzene-d6 and toluene-d8 were freeze- pump-thaw degassed and stored over 3 Å molecular sieves prior to use. NMR spectra were obtained on BRUKER 400 or 500 MHz machines, all peaks are referenced against residual solvent peak (C ₆ D ₅ H δ 7.16 ppm, C ₆ D ₅ CD ₂ H δ 2.09 ppm) with values quoted in ppm. Data were processed in MestReNova. Crystallographic data was collected using Agilent Xcalibur PX Ultra A or Agilent Xcalibur 3E diffractometers, and the structures were refined using the SHELXTL and SHELX-2013 program systems. The β-diketiminate proligands ( ^Dipp BDI)H and ( ^Dep BDI)H, complex and diarylethyne substrates were prepared according to literature procedures. “( ^Dipp BDI)H” “( ^Dep BDI)H” Solvents were freeze-pump-thaw degassed and stored over 3 Å molecular sieves prior to use. Chemicals were purchased from Sigma Aldrich, Alfa Aesar, Honeywell or Fluorochem and used without further purification unless stated. Where liquids at 25 °C, reagents were dried over 3 Å sieves and freeze-pump-thaw degassed prior to use. All gases were supplied by BOC and used without further purification or drying. Quantitative gas chromatography (GC) analyses were performed with an Agilent Technologies 7820A GC with FID detector using either an Agilent DB-WAX or HP-PLOT Q column. The carrier gas used was helium. Durene was used as internal standard. High pressure (>10 bar) reactions were performed in either a Parr Instrument Company Series 5500 HPCL 300 mL reactor or Series 4790 GP 25 mL reactor with a 4848 reactor controller. Heating was supplied by a hot plate stirrer and metal bead bath or aluminium heating block and monitored using an internal thermocouple. Stirring was provided using PTFE coated magnetic stirrers (3.0 x 0.8 x 0.8 cm for 300 mL vessel and 1.2 x 0.4 x 0.4 cm for 25 mL vessel) and both reactors were fitted with PTFE liners. Due to issues with contamination and background catalysis all PTFE liners and stirrers were subject to a rigorous cleaning procedure after each reaction. This procedure was: an acetone rinse, then an aqua regia soak (10 – 20 minutes) followed by a thorough wash with distilled water and a final rinse with acetone. This cleaning procedure was coupled with appropriate control reactions to minimise background catalysis. Example 1 Compound 1 “( ^Dipp BDI)ZnNHPh” To a clean, dry Schlenk under argon, ( ^Dipp BDI)H (5 g, 11.9 mmol) was added and dissolved in THF (20 mL). “( ^Dipp BDI)H” ⁿ BuLi (1.6 M in hexanes, 7.5 mL, 11.9 mmol) was added dropwise at -78 °C, the reaction was then allowed to warm to 25 °C and stirred for 16 h. In a separate Schlenk, anhydrous ZnCl ₂ (1.6 g, 11.9 mmol) was dissolved in THF (10 mL). The solution of ( ^Dipp BDI)Li was transferred dropwise via cannula onto the solution of ZnCl ₂ at -78 °C. This mixture was allowed to warm to 25 °C and stirred for 16 h.

“( ^Dipp BDI)Li” In a separate Schlenk, ⁿ BuLi (1.6 M in n-hexane, 7.5 mL, 11.9 mmol) was added dropwise at -78 °C to a stirred solution of aniline (1.1 mL, 11.9 mmol) in THF (15 mL), this solution was allowed to warm to 25 °C and stirred for 16 h. The solution of LiNHPh was transferred dropwise via cannula onto the solution of ( ^Dipp BDI)ZnCl at 25 °C and stirred for 16 h. “( ^Dipp BDI)ZnCl” Recrystallisation from toluene, washing with n-hexane (2 x 5 mL) and drying under vacuum yielded pure product Compound 1 as an off-white crystalline solid (3.2 g, 5.6 mmol, 42% yield). ¹ H NMR (400 MHz, C ₆ D ₆ ) δ 7.21 – 7.18 (m, 2H, p-Dipp), 7.14 – 7.12 (m, 4H, m-Dipp), 6.80 (dd, ³ JHH = 8.5, 7.2 Hz, 2H, Zn-N(m-Ph)), 6.47 (tt, ³ JHH = 7.2 Hz, ⁴ JHH = 1.1 Hz, 1H, Zn-N(p- Ph)), 5.59 (d, ³ JHH = 7.6 Hz, 2H, Zn-N(o-Ph)), 4.95 (s, 1H, backbone CH), 3.15 (hept, ³ JHH = 6.9 Hz, 4H, ⁱ Pr-CH), 2.98 (s, 1H, Zn-N(H)), 1.67 (s, 6H, backbone CH ₃ ), 1.24 (d, ³ J _HH = 6.9 Hz, 12H, ⁱ Pr-CH ₃ ), 1.14 (d, ³ J _HH = 6.9 Hz, 12H, ⁱ Pr-CH ₃ ). ¹³ C{ ¹ H} NMR (100 MHz, C ₆ D ₆ ) δ 168.9 (backbone CCH ₃ ), 154.6 (Zn-N(ipso-Ph)), 143.2 (ipso-Dipp), 141.6 (o-Dipp), 128.8 (Zn-N(m-Ph)), 126.4 (p-Dipp), 124.0 (m-Dipp), 115.8 (Zn- N(o-Ph)), 113.6 (Zn-N(p-Ph)), 94.8 (backbone CH), 28.2 ( ⁱ Pr-CH), 23.9 ( ⁱ Pr-CH ₃ ), 23.1 (backbone CH ₃ ), 23.0 ( ⁱ Pr-CH ₃ ). Anal. Calc. (found) for C ₃₅ H ₄₇ N ₃ Zn: C 73.09 (72.91) H 8.24 (8.39) N 7.31 (6.91) %. Stoichiometric reactions To investigate the activation of H ₂ by Compound 1, stoichiometric reactions with alkyne were performed, followed by protonolysis of the resultant vinyl complex using aniline. Example 2 – H ₂ activation using Compound 1, and subsequent hydrozincation of diphenylacetylene In a N2 glovebox, Compound 1 (10 mg, 0.017 mmol) and diphenylacetylene (3.1 mg, 0.017 mmol) were added to a weighing vial via C ₆ D ₆ stock solutions. Bis(trimethylsilyl)methane (1 μL, 0.005 mmol) was added directly as an internal standard. The reaction volume was made up to 0.6 mL with C ₆ D ₆ , before being transferred to a clean, dry J. Young tap NMR tube. The tube contents were freeze-pump-thaw degassed inside the glovebox and the tube was sealed under vacuum. The tube was removed from the glovebox and ~1 atm H ₂ added. An initial ¹ H NMR spectrum was recorded, and then the tube was heated to 100 °C for 18 h. A final ¹ H NMR spectrum was recorded. The resultant the vinyl complex ( ^Dipp BDI)ZnC(Ph)CHPh was submitted for crystal structure analysis by X-ray crystallography. Crystal data: C ₄₃ H ₅₂ N ₂ Zn, M = 662.23, monoclinic, P2 ₁ /n (no.14), a = 11.3784(2), b = 15.3573(3), c = 21.4017(4) Å, β = 92.5051(17)°, V = 3736.18(13) Å ³ , Z = 4, D _c = 1.177 g cm– ³ μ(Mo-Kα) = 0688 mm ^–1 T = 173 K colourless blocks Agilent Xcalibur 3 E diffractometer; 7500 independent measured reflections (R _int = 0.0187), F ² refinement, R ₁ (obs) = 0.0368, wR ₂ (all) = 0.0921, 5912 independent observed absorption-corrected reflections [|F _o | > 4σ(|F _o |), completeness to θ _full (25.2°) = 98.9%], 436 parameters. CCDC 2004167. The C24-based isopropyl group in the structure was found to be disordered. Two orientations were identified of ca.56 and 44% occupancy, their geometries were optimised, the thermal parameters of adjacent atoms were restrained to be similar, and only the non- hydrogen atoms of the major occupancy orientation were refined anisotropically (those of the minor occupancy orientation were refined isotropically). The crystal structure of ( ^Dipp BDI)ZnC(Ph)CHPh is shown in Figure 5, with 50% probability ellipsoids. Example 3 – Protonolysis of ( ^Dipp BDI)ZnC(Ph)CHPh using aniline In a N2 glovebox, the vinyl complex ( ^Dipp BDI)ZnC(Ph)CHPh (10 mg, 0.015 mmol) and aniline (1.4 μL, 0.015 mmol) were added directly to a clean, dry J. Young NMR tube. Bis(trimethylsilyl)methane (1 μL, 0.005 mmol) was added directly as an internal standard. The reaction volume was made up to 0.6 mL with C ₆ D ₆ , and the tube was sealed and removed from the glovebox. An initial ¹ H NMR spectrum was recorded, and then the reaction mixture was heated to 100 °C for 4 days. A final ¹ H NMR spectrum was recorded. These initial and final NMR spectra are shown in Figure 2. Example 4 – Cis-alkene hydrozincation using ( ^Dipp BDI)ZnH In a N2 glovebox, hydride complex ( ^Dipp BDI)ZnH (7 mg, 0.014 mmol) and cis-stilbene (2.6 μL, 0.014 mmol) were added via C ₆ D ₆ stock solutions to a clean, dry J. Young NMR tube. Bis(trimethylsilyl)methane (1 μL, 0.005 mmol) was added directly to the tube as an internal standard. The reaction volume was made up to 0.6 mL with C ₆ D ₆ , and the tube was sealed and removed from the glovebox. An initial ¹ H NMR spectrum was recorded, and then the reaction mixture was heated to 100 °C for 19 h. A final ¹ H NMR spectrum was recorded. These initial and final NMR spectra are shown in Figure 3. The NMR yield was 8%. Example 5 – Trans-alkene hydrozincation using ( ^Dipp BDI)ZnH In a N2 glovebox, hydride complex ( ^Dipp BDI)ZnH (7 mg, 0.014 mmol) and trans-stilbene (2.6 mg, 0.014 mmol) were added via C ₆ D ₆ stock solutions to a clean, dry J. Young NMR tube. Bis(trimethylsilyl)methane (1 μL, 0.005 mmol) was added directly to the tube as an internal standard. The reaction volume was made up to 0.6 mL with C ₆ D ₆ , and the tube was sealed and removed from the glovebox. An initial ¹ H NMR spectrum was recorded, and then the reaction mixture was heated to 100 °C for 15 h. A final ¹ H NMR spectrum was recorded. These initial and final NMR spectra are shown in Figure 4. The NMR yield was 14%. Catalytic alkyne hydrogenation Examples 6-13 – High pressure (>10 bar) catalytic reactions at 30 mL scale In a N2 glovebox, Compound 1, ( ^Dipp BDI)ZnNHPh (293 mg, 0.5 mmol) was weighed into a scintillation vial, dissolved in toluene (15 mL) and transferred to a clean, dry Schlenk. Alkyne (10 equiv., 5.1 mmol) was weighed into a separate scintillation vial, dissolved in toluene (15 mL) and added to the Schlenk. The alkyne compounds used are set out in Table 1 below. ~0.5 mL was taken for NMR analysis. The Schlenk was sealed and removed from the glovebox. The Schlenk was attached to a N ₂ line and the side-arm purged for 5 minutes before being opened to the gas line. The Schlenk was fitted with a subaseal and the reaction mixture transferred into the purged 300 mL pressure vessel (N ₂ 10 x 5 bar, followed by H ₂ 3 x 3 bar) using a 20 mL syringe and needle. The vessel was pressurised to 16 bar with H ₂ and sealed. The reaction was heated to 145 °C to give a final pressure of 23 bar (measured using digital manometer). Stirring was set to 900 rpm and the reaction was run for 18 h. The reaction mixture was then analysed by NMR and gas chromatography. Table 1

Examples 14-15 - High pressure (>10 bar) catalytic reactions at 7 mL scale

In a N ₂ glovebox, Compound 1, ( ^Dipp BDI)ZnNHPh (75 mg, 0.1 mmol) and alkyne (10 equiv., 1.3 mmol) were weighed into separate scintillation vials, dissolved in toluene (7.5 mL) and added to a 25 mL pressure vessel. ~0.5 mL was taken for NMR analysis. The alkyne compounds used are set out in Table 2 below. The pressure vessel was sealed and removed from the glovebox. Inlet and outlet lines were fitted to the vessel, and the inlet valve was purged for 5 minutes with N ₂ before the vessel was opened to the gas line. The vessel was then purged with N ₂ (10 x 5 bar) followed by H ₂ (3 x 3 bar), before being pressurised to 16 bar with H ₂ and sealed. The reaction was heated to 145 °C to give a final pressure of 23 bar (measured using a digital manometer). Stirring was set to 900 rpm and the reaction was run for 18 h. The reaction mixture was then analysed by NMR and gas chromatography. Table 2 The reduced selectivity with diphenylacetylene in Example 14 relative to diethylacetylene in Example 15 was attributed to unoptimized reaction conditions in the particular reactor used. It is suspected that in this particular Example the reaction was left to run for too long resulting in complete conversion to Z-alkene followed by some over-hydrogenation or isomerisation. This could be addressed by tailoring the reaction time. Comparative Example 1 - High pressure (>10 bar) reaction at 30 mL scale without catalyst The procedure as in Example 2 was carried out but in the absence of the catalyst Compound 1. The results were as follows: DFT studies into dihydrogen activation at zinc In order to explore the energetic feasibility of the dihydrogen activation process, DFT calculations were performed using the M06L functional and a hybrid basis set. In the solid state, Compound 1 possesses an arrangement in which the core of the β-diketiminate ligand, the Zn–N motif, and the phenyl ring of the anilide all lie within the same plane. This conformation is reproduced by DFT calculations and results in an electronic structure in which the frontier molecular orbitals of Compound 1 are set up to react with dihydrogen. Hence, the natural localized molecular orbitals (NLMOs) of Compound 1 allow the visualization the 2p-orbital on N and the 4s-orbital on Zn, which have been found to contribute to the HOMO and LUMO+1, respectively. The dual Lewis acidic / Lewis basic behavior of the Zn–N bond of Compound 1 was further supported by attempts to prepare an analogue of this compound. Variation of the steric demands of the ligand on zinc (Ar = 2,6- diisopropylphenyl vs 2,6-diethylphenyl) led to the isolation of the zincate complex Compound 2, in which an equiv. of Li–Cl is coordinated to the Zn–N bond: Compound 2 As shown in Figure 1, dihydrogen activation by Compound 1 was found to occur through a stepwise process involving the formation of a weakly bound encounter complex Int-1 which leads to TS-1. Int-1 is an unstable encounter complex of zinc with dihydrogen. While there is component of bonding that involves donation of electron density from the H–H bond to the vacant 4s-orbital of Zn in Int-1 it is not significant enough to assign this as a dihydrogen complex of zinc. Dihydrogen splitting occurs by translation of the H ₂ molecule across the zinc center, towards the anilide nitrogen atom, elongating both the H–H and Zn–N distances as it nears the transition state geometry. In TS-1 population of the s*-orbital of H ₂ occurs through donation of electron density from the N-based LP, breaking the H–H bond and forming Int-2 a weakly bound adduct of 2 and H ₂ NPh. Further aspects and embodiments of the present disclosure are set out in the following numbered clauses: 1. A compound according to formula (I):

(I) or a salt, solvate or hydrate thereof; wherein: Y is selected from -QR ¹ R ² , and OR ^F ; wherein Q is selected from N, P and P(=O); L is selected from -CR ⁸ -CR ⁹ -CR ¹⁰ -, -CR ⁵ -, -CR ⁶ -CR ⁷ -, -CR ^N3 -NR ^G -CR ^N4 - and -CR ^O1 -O-CR ^O2 -; either: (A) R ¹ is R ^1A , R ² is R ^2A and R ⁴ is R ^4A ; or (B) R ⁴ is R ^4A ; and R ¹ and R ² together with the Q moiety to which they are attached are joined to form a 3-6 membered heterocyclic group optionally substituted with one or more groups R ^E ; or (C) R ¹ is R ^1A ; and R ² , R ⁴ and the atoms to which they are attached form a 5-8 membered heterocyclic group, optionally substituted with one or more groups R ^D , and optionally being fused to one or more optionally substituted aryl groups; R ³ is selected from H; linear or branched unsubstituted C _1-12 aliphatic groups; C ₆ aryl, optionally substituted with one or more groups R ^A , and 5-6 membered heteroaryl, optionally substituted with one or more groups R ^B ; R ⁵ , R ⁶ , R ⁷ , R ^N3 , R ^N4 , R ^O1 and R ^O2 are each independently selected from H, linear or branched unsubstituted C _1-12 aliphatic groups, C _5-6 unsubstituted aryl or heteroaryl groups, and -NR ^N1 R ^N2 ; R ⁸ , R ⁹ and R ¹⁰ are each independently selected from H, linear or branched unsubstituted C _1-12 aliphatic groups, C _5-6 unsubstituted aryl or heteroaryl groups, and -NR ^N1 R ^N2 ; or two or more of R ⁸ , R ⁹ and R ¹⁰ , together with the atoms to which they are attached, are joined to form a monocyclic or bicyclic group, with any remaining groups of R ⁸ , R ⁹ and R ¹⁰ being selected from H, linear or branched unsubstituted C _1-4 aliphatic groups, C _5-6 unsubstituted aryl or heteroaryl groups, and -NR ^N1 R ^N2 ; R ^1A , R ^2A and R ^4A are each independently selected from H; linear or branched unsubstituted C _1-12 aliphatic groups; C ₆ aryl, optionally substituted with one or more groups R ^A ; 5-6 membered heteroaryl, optionally substituted with one or more groups R ^B ; C _6-20 aralkyl, optionally substituted with one or more groups R ^C ; and Si(C _1-6 alkyl) ₃ ; R ^N1 and R ^N2 are each independently selected from linear or branched unsubstituted C _1-6 aliphatic groups, or R ^N1 and R ^N2 together with the N atom to which they are attached are joined to form a 3-6 membered heterocyclic group optionally substituted with one or more groups R ^E ; R ^A , R ^B , R ^C , R ^D and R ^E are each independently selected from linear or branched unsubstituted C _1-6 aliphatic groups; halo; O(C _1-6 alkyl); -CF ₃ , -CF ₂ H, -CFH ₂ ; -OCF ₃ , -OCF ₂ H and -OCFH ₂ ; R ^F and R ^G are independently selected from H; C _1-12 alkyl groups; C ₆ aryl, optionally substituted with one or more groups R ^A ; 5-6 membered heteroaryl, optionally substituted with one or more groups R ^B ; C aralkyl optionally substituted with one or more groups R ^C ; -S(=O) ₂ CF ₃ ; and -C(=O)R ^H , wherein R ^H is linear or branched C _1-6 alkyl optionally substituted with one or more groups independently selected from OH and halo; with the proviso that the compound is not a compound according to formula (X): (X) wherein the group XX is selected from -N(SiMe3)2 and -NH(DIPP); and wherein DIPP is the group: . 2. A compound according to clause 1, wherein Y is QR ¹ R ² . 3. A compound according to clause 2, wherein Q is N. 4. A compound according to clause 2 or 3, wherein R ¹ is H. 5. A compound according to any one of clauses 2 to 4, wherein R ² is unsubstituted phenyl. 6. A compound according to any one of clauses 1 to 5, wherein R ³ and R ⁴ are the same. 7. A compound according to any one of clauses 1 to 6, wherein R ³ and R ⁴ are each independently selected from phenyl optionally substituted with one or more groups R ^A . 8. A compound according to clause 7, wherein R ³ and R ⁴ are each independently selected from phenyl substituted in both ortho-positions with a group R ^A . 9. A compound according to any one of clauses 1 to 8, wherein R ^A is selected from unsubstituted branched C _3-6 alkyl. 10. A compound according to any one of clauses 1 to 9, wherein L is -CR ⁸ -CR ⁹ -CR ¹⁰ -, such that the compound is a compound according to formula (IA): (IA) or a salt, solvate or hydrate thereof. 11. A compound according to clause 10, wherein R ⁸ , R ⁹ and R ¹⁰ are each independently selected from H, linear or branched unsubstituted C _1-4 aliphatic groups, C _5-6 unsubstituted aryl or heteroaryl groups, and -NR ^N1 R ^N2 . 12. A compound according to clause 10, wherein R ⁸ , R ⁹ and R ¹⁰ are each independently selected from H and methyl. 13. A compound according to any one of clauses 10 to 12, wherein R ⁹ is H. 14. A compound according to any one of clauses 10 to 13, wherein one or both of R ⁸ and R ¹⁰ is methyl. 15. A compound according to any one of clauses 1 to 14, wherein R ^4A is selected from linear or branched unsubstituted C _1-4 aliphatic groups; C ₆ aryl, optionally substituted with one or more groups R ^A ; and C _5-6 heteroaryl, optionally substituted with one or more groups R ^B . 16. A compound according to any one of clauses 1 to 15, wherein R ³ is selected from linear or branched unsubstituted C _1-4 aliphatic groups; C ₆ aryl, optionally substituted with one or more groups R ^A ; and C _5-6 heteroaryl, optionally substituted with one or more groups R ^B . 17. A compound according to any one of clauses 1 to 16, wherein the compound is: 18. A hydrogenation catalyst comprising a compound according to any one of clauses 1 to 17. 19. A method of hydrogenation of reducing or hydrogenating a double or triple bond by reaction with dihydrogen in the presence of a catalyst comprising a compound according to any one of clauses 1 to 17. 20. A method of activating dihydrogen for hydrogenation, comprising reacting dihydrogen with a catalyst comprising a compound according to any one of clauses 1 to 17. 21. A compound according to formula (VII): (VII) wherein L, R ³ and R ⁴ are as defined in any one of clauses 1 to 17; and R ¹¹ and R ¹² are each independently selected from optionally substituted (hetero)hydrocarbyl groups.

22. A method of making a compound according to formula (I):

(l) from starting materials comprising a compound according to formula (II):

(II) wherein Y, L, R ³ and R ⁴ are as defined in any one of clauses 1 to 17.

23. A method according to clause 22, comprising:

(a) reacting the compound according to formula (II) with a first metal- containing reagent to form a compound according to formula (III):

(III) wherein M is a metal atom selected from Li, Na and K; (b) reacting the compound according to formula (III) with a zinc salt ZnX ₂ to form a compound according to formula (IV): (IV) wherein X is a monovalent anion; and (c) converting the compound according to formula (IV) into the compound according to formula (I); wherein one or both of the first metal-containing reagent and the second metal-containing reagent optionally comprises ⁿ BuLi. 24. A method according to clause 23, wherein step (c) comprises reacting the compound according to formula (IV) with M’Y, wherein M’Y is optionally made by reacting a second metal-containing reagent with YH. 25. An intermediate according to formula (IV): (IV) wherein L, R ³ and R ⁴ are as defined in any one of clauses 1 to 17 and X is a monovalent anion. 26. A method of making an intermediate according to formula (IV):

(IV) comprising reacting a compound according to formula (III) with ZnX ₂ (III) wherein L, R ³ and R ⁴ are as defined in any one of clauses 1 to 17, M is a metal atom selected from Li, Na and K and X is a monovalent anion. 27. A method of making a compound according to formula (I): 3 (I) from a compound according to formula (IV):

(IV) wherein Y, L, R ³ and R ⁴ are as defined in any one of clauses 1 to 17, and X is a monovalent anion. 28. A method of making a compound according to formula (VIII): (VIII) comprising reacting a compound according to formula (I): 3 L (I) with dihydrogen (H ₂ ), wherein L, Y, R ³ and R ⁴ are as defined in any one of clauses 1 to 17.