Structural Models for the Active Site of Acetyl-CoA Synthase: Synthesis of Dinuclear Nickel Complexes Having Thiolate, Isocyanide, and Thiourea on the Nip Site

The trinuclear nickel complex [{Ni(dadtEt)}2Ni](NiBr4) (dadtEt = N,N’-diethyl-3,7-diazanonane-1,9-dithiolate) (1a), prepared by the reaction of Ni(dadtEt) and Ni(EtOH)4Br2, was found to serve as a useful synthetic precursor of various dinuclear nickel complexes modeling the active site of acetyl-CoA synthase (ACS). The reactions of 1a with 4 equiv of the potassium salts of arenethiolates in ethanol produced a series of dinuclear nickel thiolate complexes Ni(dadtEt)Ni(SAr)2 (Ar = Ph (2a), p-Tol (2b), 2,4,6-triisopropylphenyl (Tip) (2c)) in good yields. The analogous reactions of 1a with Ag(OTf) in the presence of tBuNC and (NMe2)2CS (tmtu) generated the dicationic dinuclear nickel complexes [Ni(dadtEt)Ni(tBuNC)2](OTf)2 (3) and [Ni(dadtEt)Ni(tmtu)2](OTf)2 (4), respectively. The molecular structures of 1a, 2a−c, 3, and 4 determined by X-ray analysis compare well with that of A-cluster in ACS.