Binuclear ruthenium pyridinediimine complexes {[N3]Ru}2(m-N2) (1) react rapidly with hydrogen at ambient temperature to yield paramagnetic binuclear hydride complexes, {[N3]RuH}2(m-N2) (2) ([N3] = (C5H3N(mesityl)N=CMe)2 and (4-tBu-C5H2N(mesityl)N=CMe)2). Investigation of the reaction mechanism is complicated by the presence of both diamagnetic and paramagnetic intermediates, rapid dissociation equilibria of the binuclear species, and limited solubility at low temperatures in non-reactive solvents. Introduction of a bulky substituent such as tBu to the 4-pyridine position alleviates some of these challenges by greatly reducing the rate of reaction with hydrogen and increasing solubility, allowing spectroscopic characterization of several intermediate complexes on the reaction pathway, and kinetics studies over a wide range or temperatures. Experimental and computational evidence for equilibrium coordination of H2 prior to rate-limiting intermolecular H-atom abstraction by an independent ruthenium center will be presented.

Metalloradical reactivity patterns in even-electron ruthenium complexes: Intermediates and mechanistic insight into bimetallic activation of hydrogen by H-atom transfer

251st National Meeting (2016)

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