DIPHOSPHINE-PALLADIUM AND DIPHOSPHINE-PLATINUM COMPLEXES AS CATALYSTSFOR THE BAEYER-VILLIGER OXIDATION OF KETONES - EFFECT OF THE DIPHOSPHINE, OXIDATION OF ACYCLIC KETONES, AND MECHANISTIC STUDIES

A variety of Pd and Pt complexes of the type [(P-P)M(mu-OH)](2)(2+) (M = Pd, Pt; P-P = a series of tetraphenyldiphosphines) were tested in t he Baeyer-Villiger oxidation of ketones with hydrogen peroxide. The ef fect of the diphosphine-metal ring size on the catalytic activity indi cates that the larger the ring, the better the catalyst and that, in g eneral, Pt complexes are superior. The complex modified with P-P = dpp b is the most active catalyst and allows for the first time the oxidat ion of a series of acyclic ketones. The corresponding migratory aptitu de series is in full agreement with the one known for the stoichiometr ic organic reaction employing peracids as oxidants. A test of the reac tivity of different peroxidic oxidants.(H2O2, t-BuOOH, KHSO5, carbamid e peroxide) shows that hydrogen peroxide is the most effective. A kine tic study of the oxidation of 2-methylcyclohexanone with [(dppb)Pt(mu- OH)](2)(2+) as the catalyst shows typical half-order dependence on the catalyst concentration, suggesting that the hydroxy dimer opens up to form the catalytically active species. The reaction is first order in ketone and hydrogen peroxide and is independent of the acidity of the system. The reaction is suggested to proceed via a quasi-peroxymetall acyclic intermediate and bears strong similarities to the stoichiometr ic organic reaction.