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* = n⁵-C₅Me₅; 1,5-diaza-3,7-diphosphacyclooctane, where R = Ph or tBu and R' = Bn) have been synthesized and fully characterized. Both complexes are demonstrated to be electrocatalysts for oxidation of H₂ (1 atm, 22 °C) in the presence of external base, DBU (1,8-diazabicyclo[5.4.0]undec-7-ene). The turnover frequency of 2-H is 1.2 s-1, with an overpotential at Ecat/2 of 0.45 V, 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. The different effects of H₂O for 1-H and 2-H are ascribed to different binding affinities of H₂O to the Ru center of the corresponding unsaturated species, [Cp*Ru(PPh₂NBn₂)]+ and [Cp*Ru(PPh₂NBn₂)]+. 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 pendent amines of P₂N₂ ligands for oxidation of H₂. We thank the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences and Biosciences, for supporting initial parts of the work. Current work is supported by the Center for Molecular Electrocatalysis, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences. Pacific Northwest National Laboratory is operated by Battelle for the U.S. Department of Energy.
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 1166854
- Report Number(s):
- PNNL-SA-101826; KC0302010; KC0307010
- Journal Information:
- Energy and Environmental Science, 7(11):3630-3639, Journal Name: Energy and Environmental Science, 7(11):3630-3639
- Country of Publication:
- United States
- Language:
- English
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