Article abstract of DOI:10.1016/S0022-328X(97)00073-9

A series of [M(L)('S₂C')] complexes (M = Ni^II, Pd^II, Pt^II) containing the carbene dithiolate ligand 'S₂C'^2- = 1,3-imidazolidinyl-N, N′-bis(2-benzenethiolate)(2 - ) and various C and S co-ligands have been synthesized. When treated with KCN, n-butylisonitrile, the electron-rich olefin R₂C=CR₂ [ = bis(1,3-diphenylimidazolidine-2-ylidene)], LiMe, thiolates such as SEt^-, SPh^- or o-SC₆H₄NH₂, and hydrogen sulfide, the parent complex [Ni('S₂C')]₂ · DMF (1) yields the corresponding anionic or neutral [Ni(L)('S₂C')] complexes which were isolated as [K₂(Kryptofix5)(THF)₂(μ-OH₂)][Ni(CN)('S₂C')] (2), [Ni(CNBu)('S₂C')] (3), [Ni(CR₂)('S₂C')] (4), [Li(12-crown-4)₂][Ni(CH₃)('S₂C')] (5), [NBu₄][Ni(SEt)('S₂C')] · THF (6), [Na(15-crown-5)][Ni(SPh)('S₂C')] (7), [Na(15-crown-5)][Ni(o-SC₆H₄NH₂)('S₂C')] · 0.5THF (8), and [Na(15-crown-5)][Ni(SH)('S₂C')] (9). Analogous complexes of 9 have also been obtained with Pd (10) and Pt (11). The complexes were characterized by elemental analyses and the usual spectroscopic methods. X-ray structure determinations of 2, 3, 4, 6, 9 and 10 revealed that the [M('S₂C')] fragments are stereochemically very rigid, being little influenced by the different co-ligands L. The four-coordinate metal centers exhibit an approximately square-planar coordination geometry. The 'S₂C'^2- ligands show a characteristic propeller-like twist resulting from positioning the C₆ rings of the 'S₂C' unit above and below the coordination plane. As evidenced by the molecular structures of 9 vs. 10, this twist can vary, and the 'S₂C'^2- ligand is flexible enough to accommodate also larger metal ions than Ni^II. Complexes 9-11 belong to the rare cases of isolable SH complexes. The complexes 2-11 exhibit a remarkable thermal stability (4 is stable up to 220°C), and the [M('S₂C')] fragments so far proved inert towards decomposition. When treated with Broensted acids, the general reactivity feature of all anionic [M(L)('S₂C')] complexes is release of HL and regeneration of the parent complexes [M('S₂C')]₂. The methyl complex [Li(4-crown-4)₂][Ni(CH₃)('S₂C')] (5) is one of the rare examples in which a methyl ligand binds to an [NiS] center. While the parent complex [Ni('S₂C')]₂ · DMF (1) proved unreactive towards CO, 5 readily inserts CO yielding the highly reactive acetyl derivative [Ni(COCH₃)('S₂C')]^-. This complex could not be isolated, but its formation was established by spectroscopic methods and by its subsequent reaction with PhSH yielding, among other products, the thioester CH₃COSPh. The model character of this reaction sequence for acetyl-CoA synthesis catalyzed by CO dehydrogenases is discussed.