A Series of Mononuclear Quasi-Two-Coordinate Copper(I) Complexes Employing a Sterically Demanding Thiolate Ligand

A series of two-coordinate thiolate complexes [Cu(SAr*)L] was synthesized as possible reactants in forming analogues of the active site of Mo/Cu-containing carbon monoxide dehydrogenase. Complexes with L = PPh3 (1), 2,6-lutidine (2), and the N-heterocyclic carbene (Pr2NHCMe2)-N-i (3) have been prepared by the reaction of [CuCl(PPh3)(3)] (1) or [CuBr(SMe2)] (2, 3) with ligand L and the exceptionally sterically encumbered ligand Ar*S = 2,6-bis(2,4,6-triisopropylphenyl)benzenethiolate(1-). The reaction of [CuBr(SMe2)] with the thiolate in the absence of added L afforded trinuclear [Cu-3(SAr*)(2)Br] (7). The carbene complex (3) undergoes Cu-C bond insertion with sulfur to form the thiourea complex [Cu(SAr*)(Pr(2)(i)Me(2)lmS)] (4). The complexes [Cu(Ar*)L] with L = tetrahydrothiophene (5) and 2,6-lutidine (6) were obtained by reaction of Ar*Li(OEt2) with CuBr/L. These species did not undergo clean Cu-C bond insertion with sulfur transfer agents; the disulfide Ar*SSCH2Ph (9) was isolated from the reaction of 6 with (PhCH2S)(2)S. The structures of all complexes and 9 were determined. Whereas 5 and 6 are strictly two-coordinate with linear C-Cu-L angles, 1-4 are quasi-two-coordinate because of weak 3d-C(p pi) interactions with a phenyl group, leading to nonlinear structures (S-Cu-L = 135-164 degrees).