Electrochemical oxidation of H2 catalyzed by ruthenium hydride complexes bearing P2N2 ligands with pendant amines as proton relays

Two Ru hydride complexes, Cp*Ru((P2N2Bn)-N-Ph)H (1-H) and Cp*Ru((Pt2N2Bn)-N-Bu)H (2-H) supported by cyclic (P2N2R')-N-R ligands (Cp* = eta(5)- C5Me5; (P2N2Bn)-N-R = 1,5-dibenzyl,-3,7-R-1,5-diaza-3,7-diphosphacyclooctane, where R = Ph or Bu-t) have been developed as electrocatalysts for oxidation of H-2 (1.0 atm, 22 degrees C). The turnover frequency of 2-H is 1.2 s(-1) at 22 degrees C (1.0 atm H-2) with an overpotential at E-cat/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 H-2 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 H-2.