Stoichiornetric and catalytic oxidations of alkanes and alcohols mediated by highly oxidizing ruthenium-oxo complexes bearing 6,6'-dichloro-2,2'-bipyridine

Abstract

The ruthenium(II) complex cis-[Ru(6,6'-Cl 2bpy) 2(OH 2) 2](CF 3SO 3) 2 (1) is a robust catalyst for C-H bond oxidations of hydrocarbons, including linear alkanes, using tert-butyl hydroperoxide (TBHP) as terminal oxidant. Alcohols can be oxidized by the '1 + TBHP' protocol to the corresponding aldehydes/ketones with high product yields at ambient temperature. Oxidation of 1 with Ce(IV) in aqueous solution affords cis-[Ru(VI)(6,6'-Cl 2bpy) 2O 2] 2+, which is isolated as a green/yellow perchlorate salt (2). Complex 2 is a powerful stoichiometric oxidant for cycloalkane oxidations under mild conditions. Oxidation of cis-decalin is highly stereoretentive; cis-decalinol is obtained in high yield, and formation of trans-decalinol is not observed. Mechanistic studies showing a large primary kinetic isotope effect suggest a hydrogen-atom abstraction pathway. The relative reactivities of cycloalkanes toward oxidation by 2 have been examined through competitive experiments, and comparisons with Gif-type processes are presented.