Transition-metal complexes of 1,3-dienes. Part I. Synthesis and structure of rhodium(I) complexes

Abstract

The preparation of a series of rhodium(I) complexes with halogen- or methyl-substituted 1,3-dienes by displacement of ethylene from [(C₂H₄)₂RhCl]₂and [(C₂H₄)₂Rh(acac)](acac = acetylacetonato) is described. The corresponding π-cyclopentadienyl complexes have also been prepared. The complexes have been characterized by means of ¹H n.m.r., i.r., and mass spectra and by their chemical reactions. All the dienes studied co-ordinate to the metal in a chelate fashion with the exception of 4-methylpenta-1,3-diene which co-ordinates via the unsubstituted double bond only in the case of the chloro- and acetylacetonato-complexes. In solution the latter complexes exhibit temperature-dependent rotation of the co-ordinated diene about the rhodium–olefin bond axis. Possible reasons for the different co-ordination modes are discussed.