Catalytic hydrocarbon oxygenation by ruthenium-pyridylamine complexes with alkyl hydroperoxides: a mechanistic insight

The use of TBHP (t-butyl hydroperoxide) or CHP (cumene hydroperoxide) with bis-mu-chloro Ru(II) dimers, [(RuCl)-Cl-II(L)](2)(ClO4)(2) (L = tris(2-pyridylmethyl)amine and tris(5-methyl-2-pyridylmethyl)amine), gave catalytic alkane and alkene oxygenation at 40 degrees C. These reactions were found to proceed via a Haber-Weiss-type electron-transfer reaction to generate alkoxo (RO.) and alkylperoxo (ROO.) radicals as reactive species. This electron transfer was mainly governed by the redox potentials of a complex employed as a catalyst. In addition, the environment around a ruthenium center(s) involving steric hindrance due to substituents on the pyridine rings and an intramolecular pi-pi interaction, should be also significant to regulate the reactivity of the catalyst; probably in terms of shielding of the ruthenium center(s) against the approach of peroxides to undergo the electron transfer. For those reactions with alkyl hydroperoxides, O-2 generated from peroxide decomposition plays an important role in promoting reactions as a radical chain carrier. (C) 2000 Elsevier Science S.A. All rights reserved.