Conformational Dynamics and Proton Relay Positioning in Nickel Catalysts for Hydrogen Production and Oxidation
The [Ni(PR2NR’2)2]2+ catalysts, (where PR2NR´2 is 1,5-R´-3,7-R-1,5-diaza-3,7-diphosphacyclooctane), are some of the fastest reported for hydrogen production and oxidation, however, chair/boat isomerization and the presence of a fifth solvent ligand have the potential to slow catalysis by incorrectly positioning the pendant amines or blocking the addition of hydrogen. Here, we report the structural dynamics of a series of [Ni(PR2NR’2)2]n+ complexes, characterized by NMR spectroscopy and theoretical modeling. A fast exchange process was observed for the [Ni(CH3CN)(PR2NR’2)2]2+ complexes which depends on the ligand. This exchange process was identified to occur through a three step mechanism including dissociation of the acetonitrile, boat/chair isomerization of each of the four rings identified by the phosphine ligands (including nitrogen inversion), and reassociation of acetonitrile on the opposite side of the complex. The rate of the chair/boat inversion can be influenced by varying the substituent on the nitrogen atom, but the rate of the overall exchange process is at least an order of magnitude faster than the catalytic rate in acetonitrile demonstrating that the structural dynamics of the [Ni(PR2NR´2)2]2+ complexes does not hinder catalysis. This material is based upon work supported as part of the Center for Molecular Electrocatalysis, an Energy Frontier Research Center funded by the US Department of Energy, Office of Science, Office of Basic Energy Sciences under FWP56073. Research by J.A.F., M.O., M-H. H., M.L.H, D.L.D. A.M.A., S. R. and R.M.B. was carried out in the Center for Molecular Electrocatalysis, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science. W.J.S. and S.L. were funded by the DOE Office of Science Early Career Research Program through the Office of Basic Energy Sciences. T.L. was supported by the US Department of Energy, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences & Biosciences. Pacific Northwest National Laboratory (PNNL) is a multiprogram national laboratory operated for DOE by Battelle. Computational resources were provided at W. R. Wiley Environmental Molecular Science Laboratory (EMSL), a national scientific user facility sponsored by the Department of Energy’s Office of Biological and Environmental Research located at Pacific Northwest National Laboratory; the National Energy Research Scientific Computing Center (NERSC) at Lawrence Berkeley National Laboratory; and the Jaguar supercomputer at Oak Ridge National Laboratory (INCITE 2008-2011 award supported by the Office of Science of the U.S. DOE under Contract No. DE-AC0500OR22725).
- Research Organization:
- Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Oak Ridge Leadership Computing Facility (OLCF); Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Environmental Molecular Sciences Lab. (EMSL)
- Sponsoring Organization:
- USDOE Office of Science (SC)
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 1114885
- Report Number(s):
- PNNL-SA-97203; 44681; 39981; KC0307010
- Journal Information:
- Organometallics, 32(23):7034-7042, Journal Name: Organometallics, 32(23):7034-7042
- Country of Publication:
- United States
- Language:
- English
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