Speciation and decomposition pathways of ruthenium catalysts used for selective C–H hydroxylation

Abstract

Mechanistic insight into a C–H hydroxylation reaction catalysed by [(Me₃tacn)RuCl₃] has been obtained using desorption electrospray ionization mass spectrometry (DESI-MS) to identify reactive intermediates and to determine the fate of the starting metal complex. Our studies provide direct evidence for the formation of a high-valent dioxo-Ru(VI) species, which is believed to be the active oxidant. Other unexpected Ru-oxo intermediates, however, have been identified and may also function as competent hydroxylating agents. Mass spectral data that substantiate putative mechanisms for catalyst arrest and highlight reactivity differences between [(Me₃tacn)RuCl₃] and the corresponding tribromide adduct are also described.