Übergangsmetallkomplexe mit Schwefelliganden CXXIV. Koordination von C- und S-Liganden an Metall—Carben—Thiolat-Fragmente [M(‘S 2C’)] [M = Ni II, Pd II, Pt II; ‘S 2C’ 2− = 1,3-Imidazolidinyl- N,N′-bis(2-benzolthiolat)(2 −)]. [M(L)(‘S 2C’)]-Komplexe mit L = CN −, CH 3−, COCH 3−, CNBu, CR 2, SH − und SR − (R = Et, Ph, o-C 6H 4NH 2)

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A series of [M(L)(‘S 2C’)] complexes (M = Ni II, Pd II, Pt II) containing the carbene dithiolate ligand ‘S 2C’ 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 R 2C=CR 2 [=bis(1,3-diphenylimidazolidine-2-ylidene)], LiMe, thiolates such as SEt −, SPh − or o-SC 6H 4NH 2, and hydrogen sulfide, the parent complex [Ni(‘S 2C’)] 2 · DMF ( 1) yields the corresponding anionic or neutral [Ni(L)(‘S 2C’)] complexes which were isolated as [K 2(Kryptofix5)(THF) 2(μ-OH 2)][Ni(CN)(‘S 2C’)] ( 2), [Ni(CNBu)(‘S 2C’)] ( 3), [Ni(CR 2)(‘S 2C’)] ( 4), [Li(12-crown-4) 2][Ni(CH 3)(‘S 2C’)] ( 5), [NBu 4][Ni(SEt)(‘S 2C’)] · THF ( 6), [Na(15-crown-5)][Ni(SPh)(‘S 2C’)] ( 7), [Na(15-crown-5)][Ni( o-SC 6H 4NH 2)(‘S 2C’)] · 0.5THF ( 8), and [Na(15-crown-5)][Ni(SH)(‘S 2C’)] ( 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(‘S 2C’)] 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 ‘S 2C’ 2− ligands show a characteristic propeller-like twist resulting from positioning the C 6 rings of the ‘S 2C’ 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 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(‘S 2C’)] fragments so far proved inert towards decomposition. When treated with Brönsted acids, the general reactivity feature of all anionic [M(L)(‘S 2C’)] complexes is release of HL and regeneration of the parent complexes [M(‘S 2C’)] 2. The methyl complex [Li(4-crown-4) 2][Ni(CH 3)(‘S 2C’)] ( 5) is one of the rare examples in which a methyl ligand binds to an [NiS] center. While the parent complex [Ni(‘S 2C’)] 2 · DMF ( 1) proved unreactive towards CO, 5 readily inserts CO yielding the highly reactive acetyl derivative [Ni(COCH 3)(‘S 2C’)] −. 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 CH 3COSPh. The model character of this reaction sequence for acetyl—CoA synthesis catalyzed by CO dehydrogenases is discussed.