MechanisticStudy of Ruthenium-Catalyzed C–HHydroxylation Reveals an Unexpected Pathway for Catalyst Arrest

We have recently disclosed [(dtbpy)2RuCl2] as an effective precatalyst for chemoselective C–H hydroxylation of C(sp3)–H bonds and have noted a marked disparity in reaction performance between 4,4′-di-tert-butyl-2,2′-bipyridine (dtbpy)- and 2,2′-bipyridine (bpy)-derived complexes. A desire to understand the origin of this difference and to further advance this catalytic method has motivated the comprehensive mechanistic investigation described herein. Details of this reaction have been unveiled through evaluation of ligand structure–activity relationships, electrochemical and kinetic studies, and pressurized sample infusion high-resolution mass spectrometry (PSI-MS). Salient findings from this investigation include the identification of more than one active oxidant and three disparate mechanisms for catalyst decomposition/arrest. Catalyst efficiency, as measured by turnover number, has a strong inverse correlation with the rate and extent of ligand dissociation, which is dependent on the identity of bipyri...