System with Potential Dual Modes of Metal-Ligand Cooperation: Highly Catalytically Active Pyridine-Based PNNH-Ru Pincer Complexes

Metal–ligand cooperation (MLC) plays an important role in catalysis. Systems reported so far are generally based on a single mode of MLC. We report here a system with potential for MLC by both amine–amide and aromatization–dearomatization ligand transformations, based on a new class of phosphino–pyridyl ruthenium pincer complexes, bearing sec‐amine coordination. These pincer complexes are effective catalysts under unprecedented mild conditions for acceptorless dehydrogenative coupling of alcohols to esters at 35 °C and hydrogenation of esters at room temperature and 5 atm H2. The likely actual catalyst, a novel, crystallographically characterized monoanionic de‐aromatized enamido–RuII complex, was obtained by deprotonation of both the NH and the methylene proton of the N‐arm of the pincer ligand. Cooperation with a pinch! Ruthenium complexes with potential for dual‐modes of metal–ligand cooperation, involving amine–amide and aromatization–dearomatization modes, catalyze dehydrogenative coupling of primary alcohols and hydrogenation of esters under previously unseen mild conditions. Deprotonation of such a complex has led to a new monoanionic dearomatized complex.