We report the synthesis and structure of three structurally-related mononuclear S-ligated Ni (I1) complexes, 6-coordinate [ N~( L S~N Z ) ( M~C N ) ]~+ (1; LS3NZ = ( H z N C Z H~S C~H~)~S ) , 6-coordinate [Ni(BATES)Cl]+ (%BATES = ( H~N -~-C~H~S C Z H~) Z S ) , and 5-coordinate Ni(Lss) (3; Ls5 = (-%-C~H~SCZ&)~S), which contain Ni in a S-rich environment possibly resembling that of the active form of nickel hydrogenases. Complex 1 crystallizes in the monoclinic space group P21/n with a = 19.036(2) A, b = 12.022(8) A, c = 24.953(4) A, / 3 = 107.78(1)', and 2 = 4. Complex 2 crystallizes in the space group P i with a = 11.213(1) A, b = 13.482(2) A, c = 14.414(2) A, a = 72.82(1)', @ = 89.862(9)', y = 69.396(9)', and Z = 2. Complex 3 crystallizes in the monoclinic space group P2l/c with u = 10.759(2) A, b = 11.251(3) A, c 14.198(1) A, @ = 90.82(1)', and 2 = 4. Structures 1-3 share a common trithioether (Sapial(C~H4SRcq)2; I & = C2H4NH2 (l), CaH4NH2 (2), or CsHdS-(3)) "backbone" and possess either a "vacant" or a labile coordination site. These structures differ in terms of their molecular charge (2+ (l), 1+ (2), 0 (3)) and terminal ligating atoms. The amine-ligated complexes 1 and 2 have a higher affinity for axial ligands and are more reactive than the thiolate-ligated complex 3. The Ni-bound MeCN solvent molecule of 1 is exchangeable and readily displaced by weaker coordinating solvents, as well as anionic ligands. X-ray structures of the most stable derivatives of 1, [Ni(Ls3~z)(py)]~' (7), [N~(Ls~Nz)(N~)]+ (81, and [Ni(Ls3~2)(Cl)]+ (9), are presented, and structural parameters are compared for [N~(Ls~Nz)(L)]"' (n = 1,2; L = MeCN (l), py (7), N3-(8), C1-(9), and B r (4)). Reaction of 2 with NaBH4 at 4 2 'C affords a thermally unstable species 10, which behaves like a Ni-H in terms of its reactivity. Hydridederivative 10 will hydrogenate olefins (styrene and cyclohexene) and convert CDCl3 to CHDClZ, In contrast to the amine-ligated complexes, thiolate-ligated 3 is fairly unreactive with respect to binding axial ligands. The only ligand examined in this study which was strong enough to induce the spin-state change required in converting 3 to a 6-coordinate structure was pyridine. Implications that this observed decrease in reactivity, upon substitution of terminal amines with aromatic thiolates, has with respect to the probable structure of the Ni-binding site of hydrogenase is also discussed.Research efforts in our group have been directed toward the design and synthesis of mononuclear Ni complexes which contain Ni in a S-rich environment resembling that of the reactive, reduced form of Ni hydrogenases (H2-ases) l4 and which incorporate features designed to promote reactivity. The Ni site in Hz-ases catalyzes H+/D2 exchange, HZ activation and oxidation, or, in some cases, Hz evolution. Although the Ni sites do not appear to be identical for all Hz-ases, all of them are mononuclear, redox t In this paper, boldface numbers denoting chemical species may refer to 0 Abstract published in Aduance ACS Abstracts, October 15, 1...

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