Proton magnetic resonance and mass spectra of some isoleptic transition-metal π-allyl complexes

Abstract

The n.m.r. spectra of the isoleptic complexes M(C₃H₅)₂(M = Ni, Pd, Pt) and M(C₃H₅)₄(M = Zr, Hf) are reported. The nickel, palladium, and zirconium complexes all give, at sufficiently low temperatures, spectra corresponding to structures with equivalent symmetrically bonded π-allylic ligands in which rotation of the CH₂ groups is absent or slow. The nickel and palladium complexes each consist of two isomers of this type in equilibrium. At higher temperatures the spectra of the zirconium and palladium complexes undergo changes corresponding to increased internal rotation of the CH₂ groups. The hafnium complex has a spectrum corresponding to rapid internal rotation throughout the temperature range studied. The platinum complex gives a spectrum which is best interpreted by assuming that both allylic ligands are equivalent, but each is unsymmetrically bonded to the metal atom.

The mass spectra of the isoleptic complexes studied all show parent ions. The degree of fragmentation is very small under field-ionisation conditions but much more extensive under electron impact, and differences in fragmentation patterns are discussed.