Heteronuclear complexes containing Group 6 transition metals; chemical, spectroscopic, and theoretical studies on some binuclear complexes and the X-ray crystal structure determination of [WNi(CO)3(PPh3)2(η5-C5H5)

Abstract

Reactions of anions [M(CO)3(η5-C5H5)]– with [NiCl2(PPh3)2] in tetrahydrofuran afford paramagnetic, bimetallic complexes [MNi(CO)3(PPh3)2(η5-C5H5)][M = Mo (1) or W (2)], and a less stable chromium analogue [M = Cr (3)], as green crystalline solids. Ready cleavage of these bimetallic complexes occurs, as on reaction with CO or Ph2PCH2CH2PPh2, and related reactions of [WRh(CO)3(PPh3)2(η5-C5H5)](5) are also presented. An X-ray diffraction study of crystalline (2)[monoclinic, space group P21/c, a= 17.873(9), b= 10.156(6), c= 21.249(7)Å, β= 105.05(3)°, Z= 4] establishes the structure [(η5-C5H5)(OC)W(µ-CO)2Ni(PPh3)2](R= 0.062, R′= 0.087) with semibridging CO groups and a relatively short W–Ni separation [2.574(3)Å]. Spectroscopic studies on complexes (1)–(3) include analyses of e.s.r. spectra both in solution, where coupling to inequivalent 31P nuclei is observed, and in the solid state. Comparative extended-Hückel molecular orbital studies on model complexes [MM′(CO)3(PH3)2(η5-C5H5)][M = Mo, M′= Rh; M = W, M′= Ni or Cu (two conformers)] are discussed and the bonding analysed in terms of both direct M–M′ and semibridging M(µ-CO)M′ interactions. Cyclic voltammetry of complexes (2), (5), and [WCu(CO)3(PPh3)2(η5-C5H5)] is reported and simple redox processes occur for (2) and (5).