Preparation and spectra of a series of tautomeric compounds, [NiCo(η-dienyl)(CO)4L](dienyl = C5H5 or C5H4Me; L = tertiary phosphine or arsine)

Abstract

A number of [NiCo(η-dienyl)(CO)₄L] complexes (dienyl = C₅H₅ or C₅H₄Me; L = tertiary phosphine or arsine) have been prepared from [Ni(η-dienyl)LBr] and Na[Co(CO)₄] in tetrahydrofuran solution. During this reaction the ligand L migrates from Ni to Co. Infrared, ¹H n.m.r., and mass spectroscopy have been used to investigate the structure of these compounds, which in solution exist as an equilibrium mixture of isomers. One has the [(η-dienyl)(OC)NiCo(CO)₃L] structure with no bridging CO groups. The remainder contain the Ni(µ-CO)₂Co moiety, and structures are suggested for them. The equilibria are affected by changes of solvent, temperature, and the η-dienyl and L ligands. Variable-temperature ¹H n.m.r. spectroscopic studies on [NiCo(η-C₅H₅)(CO)₄{P(C₆H₄F-p)₃}] show that at room temperature the interconversion of isomers is slow on the n.m.r. time scale.