TRANSITION-METAL COMPLEXES WITH SULFUR LIGANDS .124. COORDINATION OF C AND S LIGANDS ON METAL-CARBENE-THIOLATE FRAGMENTS [M(S2C)] [M = NI(II), PD(II), PT(II), S2C(2-) = 1,3-IMIDAZOLIDINYL-N,N'-BIS-(2-BENZENETHIOLATE) (2-)] - [M(L) (S2C)] COMPLEXES WHERE L = CN-, CH3-, COCH3-, CNBU, CR-2, SH- AND SR- (R = ET, PH, ORTHO-C6H4NH2)

A series of [M(L)('S2C')] complexes (M = Ni-II, Pd-II, Pt-II) containi ng the carbene dithiolate ligand 'S2C'(2-)= 1,3-imidazolidinyl-N,N'-bi s(2-benzenethiolate)(2-) and various C and S co-ligands have been synt hesized. When treated with KCN, n-butylisonitrile, the electron-rich o lefin R2C=CR2 [= bis(1,3-diphenylimidazolidine-2-ylidene) LiMe, thiola tes such as SEt-, SPh- or o-SC6H4NH2, and hydrogen sulfide, the parent complex [Ni('S2C')](2).DMF (1) yields the corresponding anionic or ne utral [Ni(L)('S2C')] complexes which were isolated as [K-2(Kryptofix5) (THF)(2)(mu-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) a nd Pt (II). 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')I fragments are stereoch emically very rigid, being little influenced by the different co-ligan ds L. The four-coordinate metal centers exhibit an approximately squar e-planar coordination geometry. The 'S2C'(2) ligands show a characteri stic propeller-like twist resulting from positioning the C-6 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 'S 2C'(2-) ligand is flexible enough to accommodate also larger metal ion s than Ni-II. Complexes 9-11 belong to the rare cases of isolable SH c omplexes. The complexes 2-11 exhibit a remarkable thermal stability (4 is stable up to 220 degrees C), and the [M('S2C')] fragments so far p roved inert towards decomposition. When treated with Bronsted acids, t he general reactivity feature of all anionic [M(L)('S2C')] complexes i s 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. W hile the parent complex [Ni('S2C')](2).DMF (1) proved unreactive towar ds CO, 5 readily inserts CO yielding the highly reactive acetyl deriva tive [Ni(COCH3)('S2C')](-). This complex could not be isolated, but it s formation was established by spectroscopic methods and by its subseq uent 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. (C) 1997 Elsev ier Science S.A.