Wingtip substituents tailor the catalytic activity of ruthenium triazolylidene complexes in base-free alcohol oxidation

A series of RuII (η6-arene) complexes with 1,2,3-triazolylidene ligands comprising different aryl and alkyl wingtip groups have been prepared and characterized by NMR spectroscopy, microanalysis, and in one case by X-ray diffraction. All complexes are active catalyst precursors for the oxidation of alcohols to the corresponding aldehydes/ketones without the need of an oxidant or base as additive. The wingtip groups have a direct impact on the catalytic activity, alkyl wingtips providing the most active species while aryl wingtip groups induce lower activity. An N-bound phenyl group was the most inhibiting wingtip group due to cyclometalation. Arene dissociation was observed as a potential catalyst deactivation pathway.