Olefin rotation in platinum(II) olefin complexes. Part II

Abstract

The preparation and n.m.r. spectra of compounds of type PtX(acac)(olefin)(acac = MeCO·CH·COMe^–; X = Cl, olefin = ethylene, propene, cis- and trans-but-2-ene, and tetramethylethylene. X = Br; olefin = ethylene, propene, cis- and trans-but-2-ene) are described. Olefin rotation has been detected in all the complexes studied and estimates of the rate of rotation have been obtained. The data indicate that substitutions on the acetylacetone ring or changing X from chloride to bromide have little influence on the free energy of activation of the olefin reorientation. The internal nuclear spin coupling constants of the olefin suggest that the internal bonding of the olefin is modified by co-ordination to the platinum. The platinum–proton coupling constants show that the olefin assumes a skewed position to the plane perpendicular to the platinum–ligand plane in these complexes.