PROCESS

The present invention relates to a process for the production of hydrogen comprising contacting at least one complex of formula (I), (I) wherein: X- is an anion; M is a metal selected from Ru, Os, Fe, Co and Ni; D is optionally present and is one or more monodentate or multidentate donor ligands; Y1 is selected from CR13, B and N; Z1 and Z2 are each independently selected from =N, =P, NR14, PR15, O, S and Se; or Z2 is a direct bond between carbocyclic ring B and substituent R4; each of A and B is independently a saturated, unsaturated or partially unsaturated carbocyclic hydrocarbon ring; R3 and R4 are each independently selected from H, C1-6-alkyl, aryl and C1-6-haloalkyl, and a linker group optionally attached to a solid support; or R3 and R4 together form the following moiety: (AB) Y2 is a direct single bond or double bond, or is CR18; R1, R2, R5-13 and R16-18 are each independently selected from H, C1-6-alkyl, C2-6-alkenyl, C2-6-alkynyl, aryl, C1-6-haloalkyl, NR19R20 and a linker group optionally attached to a solid support; or two or more of said R1-13 and R16-18 groups are linked, together with the carbons to which they are attached, to form a saturated or unsaturated hydrocarbon group; R14, R15, R19 and R20 are each independently selected from H, C1-6-alkyl, C2-6-alkenyl, C2-6-alkynyl, aryl, C1-6-haloalkyl, and a linker group optionally attached to a solid support; with at least one substrate of formula (II), R21R22NH-BHR23R24, wherein R21 to R24 are each independently selected from H, C1-6-alkyl, fluoro- substituted C1-6-alkyl, C6-14-aryl and C6-14-aralkyl, or any two of R21, R22, R23 and R24 are linked to form a C3-10-alkylene group or C3-10-alkenylene group, which together with the nitrogen and/or boron atoms to which they are attached, forms a cyclic group; or a substrate comprising two, three or four substrates of formula (II) linked via one or more bridging groups so as to form a dimeric, trimeric or tetrameric species, and wherein the bridging group is selected from straight or branched C1-6-alkylene optionally substituted by one or more fluoro groups, boron, C6-14-aryl and C6-14-aralkyl; or a substrate comprising two, three or four substrates of formula (II) which are joined so as to form a fused cyclic dimeric, trimeric or tetrameric species. Further aspects of the invention relate to a hydrogen generation system comprising a complex of formula (I), a substrate of formula (II) and a solvent, and to the use of complexes of formula (I) in fue