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-μ-chloro Ru(II) dimers, [RuIICl(L)]2(ClO4)2 (L=tris(2-pyridylmethyl)amine and tris(5-methyl-2-pyridylmethyl)amine), gave catalytic alkane and alkene oxygenation at 40°C. These reactions were found to proceed via a Haber–Weiss-type electron-transfer reaction to generate alkoxo (ROradical dot) and alkylperoxo (ROOradical dot) 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 π–π 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, O2 generated from peroxide decomposition plays an important role in promoting reactions as a radical chain carrier.