ZEROVALENT PLATINUM CHEMISTRY .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

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 C=O 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.