Electrochemical oxidation of H2 catalyzed by ruthenium hydride complexes bearing P2N2 ligands with pendant amines as proton relays
Two Ru hydride complexes, Cp*Ru(PPh2NBn2)H (1-H) and Cp*Ru(PtBu2NBn2)H (2-H) supported by cyclic PR2NR′2 ligands (Cp* = η5-C5Me5; PR2NBn2 = 1,5-dibenzyl,-3,7-R-1,5-diaza-3,7-diphosphacyclooctane, where R = Ph or tBu) have been developed as electrocatalysts for oxidation of H2 (1.0 atm, 22 °C). The turnover frequency of 2-H is 1.2 s−1 at 22 °C (1.0 atm H2) with an overpotential at Ecat/2 of 0.5 V in the presence of exogenous base, DBU (1,8-diazabicyclo[5.4.0]undec-7-ene), while catalysis by 1-H has a turnover frequency of 0.6 s−1 and an overpotential of 0.6 V at Ecat/2. Addition of H2O facilitates oxidation of H2 by 2-H and increases its turnover frequency to 1.9 s−1, while H2O slows down the catalysis by 1-H. In addition, studies of Cp*Ru(dmpm)H (where dmpm = bis(dimethylphosphino)methane), a control complex lacking pendent amines in its diphosphine ligand, confirms the critical roles of the pendant amines of the P2N2 ligands as proton relays in the oxidation of H2.