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Title: Nature of Hydrogen Interactions with Ni(II) Complexes Containing Cyclic Phosphine Ligands with Pendant Nitrogen Bases

Abstract

Studies of the role of proton relays in molecular catalysts for the electrocatalytic production and oxidation of H2 have been carried out. The electrochemical production of hydrogen from protonated DMF solutions catalyzed by [Ni(P2PhN2Ph)2(CH3CN)](BF4)2, 3a, (where P2PhN2Ph is 1,3,5,7-tetraphenyl-1,5-diaza-3,7-diphosphacyclooctane) permits a limiting value of the H2 production rate to be determined. The turnover frequency of 350 s-1 establishes that the rate of H2 production for the mononuclear nickel catalyst 3a is comparable to those observed for Ni-Fe hydrogenase enzymes. In the electrochemical oxidation of hydrogen catalyzed by [Ni(P2CyN2Bz)2](BF4)2, 3b, (where Cy is cyclohexyl and Bz is benzyl), the initial step is the reversible addition of hydrogen to 3b (Keq = 190 atm-1 at 25oC). The hydrogen addition product exists as three nearly iso-energetic isomers 4A-C, which have been identified by a combination of one and two dimensional 1H, 31P and 15N NMR spectroscopies as Ni(0) complexes with a protonated amine in each cyclic ligand. The nature of the isomers, together with calculations, suggest a mode of hydrogen activation that involves a symmetrical interaction of a nickel dihydrogen ligand with two amine bases in the diphosphine ligands. Single deprotonation of 4 by an external base results in a rearrangement to [HNi(P2CyN2Bz)2](BF4),more » 5, and this reaction is reversed by the addition of a proton to the nickel hydride complex. The small energy differences associated with significantly different distributions in electron density and protons within these molecules may contribute to their high catalytic activity. This work was supported by the Office of Basic Energy Sciences of the US Department of Energy. The Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy.« less

Authors:
; ; ; ; ;
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
909679
Report Number(s):
PNNL-SA-53453
Journal ID: ISSN 0027-8424; PNASA6; KC0302010; TRN: US200723%%131
DOE Contract Number:
AC05-76RL01830
Resource Type:
Journal Article
Resource Relation:
Journal Name: Proceedings of the National Academy of Sciences of the United States of America, 104(17):6951-6956; Journal Volume: 104; Journal Issue: 17
Country of Publication:
United States
Language:
English
Subject:
08 HYDROGEN; 36 MATERIALS SCIENCE; ELECTRON DENSITY; HYDROGEN; HYDROGEN ADDITIONS; LIMITING VALUES; NICKEL; NICKEL HYDRIDES; NITROGEN; PHOSPHINES; PRODUCTION; proton relays; molecular catalysts; electron density; hydrogen interactions

Citation Formats

Wilson, Aaron, Shoemaker, R. K., Miedaner, Alex, Muckerman, J. T., DuBois, Daniel L., and DuBois, Mary R.. Nature of Hydrogen Interactions with Ni(II) Complexes Containing Cyclic Phosphine Ligands with Pendant Nitrogen Bases. United States: N. p., 2007. Web. doi:10.1073/pnas.0608928104.
Wilson, Aaron, Shoemaker, R. K., Miedaner, Alex, Muckerman, J. T., DuBois, Daniel L., & DuBois, Mary R.. Nature of Hydrogen Interactions with Ni(II) Complexes Containing Cyclic Phosphine Ligands with Pendant Nitrogen Bases. United States. doi:10.1073/pnas.0608928104.
Wilson, Aaron, Shoemaker, R. K., Miedaner, Alex, Muckerman, J. T., DuBois, Daniel L., and DuBois, Mary R.. Tue . "Nature of Hydrogen Interactions with Ni(II) Complexes Containing Cyclic Phosphine Ligands with Pendant Nitrogen Bases". United States. doi:10.1073/pnas.0608928104.
@article{osti_909679,
title = {Nature of Hydrogen Interactions with Ni(II) Complexes Containing Cyclic Phosphine Ligands with Pendant Nitrogen Bases},
author = {Wilson, Aaron and Shoemaker, R. K. and Miedaner, Alex and Muckerman, J. T. and DuBois, Daniel L. and DuBois, Mary R.},
abstractNote = {Studies of the role of proton relays in molecular catalysts for the electrocatalytic production and oxidation of H2 have been carried out. The electrochemical production of hydrogen from protonated DMF solutions catalyzed by [Ni(P2PhN2Ph)2(CH3CN)](BF4)2, 3a, (where P2PhN2Ph is 1,3,5,7-tetraphenyl-1,5-diaza-3,7-diphosphacyclooctane) permits a limiting value of the H2 production rate to be determined. The turnover frequency of 350 s-1 establishes that the rate of H2 production for the mononuclear nickel catalyst 3a is comparable to those observed for Ni-Fe hydrogenase enzymes. In the electrochemical oxidation of hydrogen catalyzed by [Ni(P2CyN2Bz)2](BF4)2, 3b, (where Cy is cyclohexyl and Bz is benzyl), the initial step is the reversible addition of hydrogen to 3b (Keq = 190 atm-1 at 25oC). The hydrogen addition product exists as three nearly iso-energetic isomers 4A-C, which have been identified by a combination of one and two dimensional 1H, 31P and 15N NMR spectroscopies as Ni(0) complexes with a protonated amine in each cyclic ligand. The nature of the isomers, together with calculations, suggest a mode of hydrogen activation that involves a symmetrical interaction of a nickel dihydrogen ligand with two amine bases in the diphosphine ligands. Single deprotonation of 4 by an external base results in a rearrangement to [HNi(P2CyN2Bz)2](BF4), 5, and this reaction is reversed by the addition of a proton to the nickel hydride complex. The small energy differences associated with significantly different distributions in electron density and protons within these molecules may contribute to their high catalytic activity. This work was supported by the Office of Basic Energy Sciences of the US Department of Energy. The Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy.},
doi = {10.1073/pnas.0608928104},
journal = {Proceedings of the National Academy of Sciences of the United States of America, 104(17):6951-6956},
number = 17,
volume = 104,
place = {United States},
year = {Tue Apr 24 00:00:00 EDT 2007},
month = {Tue Apr 24 00:00:00 EDT 2007}
}