Zerovalent platinum chemistry. Part 12. Unexpected reactivity of [Pt(PPh3)2(O2)] towards ortho and para quinones and the structures of 1 : 1 adducts with p-benzoquinone and 1,4-naphthoquinone

Abstract

The reaction of [Pt(PPh₃)₂(O₂)] with both o- and p-benzoquinones produces only 1 : 1 adducts characterised by a pseudo-ozonide metallacycle involving one carbonyl group with a spiranic steric arrangement. Strangely the second carbonyl group of the quinone does not react with an excess of [Pt(PPh₃)₂(O₂)]. The X-ray structures of the adducts with p-benzoquinone and 1,4-naphthoquinone show a skew conformation of the metallacycle with the quinone moiety still planar. Reaction with [Pt(PPh₃)₂(O₂)] produces only a slight perturbation of the π-electronic conjugated structure of the quinone, since the CO bond length of the free carbonyl group does not change. Molecular models suggest the absence of steric hindrance for a second pseudo-ozonide metallacycle involving the para carbonyl group. It is suggested that the lack of reactivity could be of kinetic origin.