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).