Heteronuclear transition metal–alkyne clusters. Part 1. Reactions of tris(alkyne)monocarbonyltungsten complexes with octacarbonyldicobalt. Synthesis, X-ray crystal structure, and two-dimensional nuclear magnetic resonance studies of [WCo2(µ-C2Et2)(µ-C4Et4)(CO)8]

Abstract

Reactions between the compounds [W(C₂R₂)₃(CO)](R = Et or Pr) and [Co₂(CO)₈] afford the trinuclear metal complexes [WCo₂(µ-C₂R₂)(µ-C₄R₄)(CO)₈]. The molecular structure of [WCo₂-(µ-C₂Et₂)(µ-C₄Et₄)(CO)₈] has been established by an X-ray diffraction study. The structure has a non-linear open chain of metal atoms [Co–W–Co 153.6(1)°] in which one tungsten–cobalt bond [2.732(1)Å] is bridged by a 3-hexyne ligand in a perpendicular co-ordination mode, while the second tungsten–cobalt bond [2.673(1)Å] is bridged by an alkyne-derived butadiene ligand, π-bound to tungsten and σ-bound to cobalt. The cobalt atoms are also ligated by three terminal carbonyl groups and the tungsten by two such groups. A full assignment of the ¹H and ¹³C-{¹H} spectra of [WCo₂(µ-C₄Et₄)(µ-C₄Et₄)(CO)₈] using two-dimensional [¹H-¹H] and [¹³C-¹H]-COSY n.m.r. spectroscopy reveals that alkyne rotation does not occur on the n.m.r. time-scale, although fluxional processes produce a mirror plane through the three metals. The complex [WCo₂(µ-C₂Et₂)-(µ-C₄Et₄)(CO)₈] reacts with P(OMe)₃ to afford [WCo₂(µ-C₂Et₂)(µ-C₄Et₄)(CO)₇{P(OMe)₃}] in which carbonyl substitution at a cobalt centre has occurred.