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Title: Nickel Bis-Diphosphine Complexes: Controlling the Binding and Heterolysis of H 2

Authors:
 [1];  [1];  [1];  [1]
  1. Center for Molecular Electrocatalysis, Physical Sciences Division, Pacific Northwest National Laboratory, P.O. Box 999, K2-57, Richland, Washington 99352, United States
Publication Date:
Research Org.:
Energy Frontier Research Centers (EFRC) (United States). Center for Molecular Electrocatalysis (CME)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1388868
DOE Contract Number:
AC05-76RL01830
Resource Type:
Journal Article
Resource Relation:
Journal Name: Organometallics; Journal Volume: 35; Journal Issue: 17; Related Information: CME partners with Pacific Northwest National Laboratory (lead); University of Illinois, Urbana-Champaign; Pennsylvania State University; University of Washington; University of Wyoming
Country of Publication:
United States
Language:
English
Subject:
catalysis (homogeneous), catalysis (heterogeneous), solar (fuels), bio-inspired, energy storage (including batteries and capacitors), hydrogen and fuel cells, charge transport, materials and chemistry by design, synthesis (novel materials)

Citation Formats

Stolley, Ryan M., Darmon, Jonathan M., Das, Parthapratim, and Helm, Monte L.. Nickel Bis-Diphosphine Complexes: Controlling the Binding and Heterolysis of H2. United States: N. p., 2016. Web. doi:10.1021/acs.organomet.6b00486.
Stolley, Ryan M., Darmon, Jonathan M., Das, Parthapratim, & Helm, Monte L.. Nickel Bis-Diphosphine Complexes: Controlling the Binding and Heterolysis of H2. United States. doi:10.1021/acs.organomet.6b00486.
Stolley, Ryan M., Darmon, Jonathan M., Das, Parthapratim, and Helm, Monte L.. 2016. "Nickel Bis-Diphosphine Complexes: Controlling the Binding and Heterolysis of H2". United States. doi:10.1021/acs.organomet.6b00486.
@article{osti_1388868,
title = {Nickel Bis-Diphosphine Complexes: Controlling the Binding and Heterolysis of H2},
author = {Stolley, Ryan M. and Darmon, Jonathan M. and Das, Parthapratim and Helm, Monte L.},
abstractNote = {},
doi = {10.1021/acs.organomet.6b00486},
journal = {Organometallics},
number = 17,
volume = 35,
place = {United States},
year = 2016,
month = 8
}
  • Nickel and palladium complexes of the type (M(L{sub 2}){sub 2})(BF{sub 4}){sub 2} and (M(L{sub 2})(L{sub 2}{prime}))(BF{sub 4}){sub 2} (where L{sub 2} and L{sub 2}{prime} are diphosphine ligands) have been synthesized. The lowest energy electronic absorption band for the nickel complexes decreases in energy as the bite size of the diphosphine ligand increases. Similarly, the half-wave potentials for the Ni(II/I) and Pd(II/O) couples become more positive as the bite size increases. Structural studies of (Ni(dppm){sub 2})(BF{sub 4}){sub 2} (where dppm is bis(diphenylphosphino)methane) and (Ni-(dppb){sub 2})(PF{sub 6}){sub 2} (where dppb is 1,2-bis(diphenylphosphino)benzene) show that increasing the bite size of the diphosphine ligandsmore » results in larger tetrahedral distortions. The crystal structure of (Ni(Dppm){sub 2})(BF{sub 4}){sub 2}(C{sub 50}H{sub 44}B{sub 2}F{sub 8}NiP{sub 4}) and (Ni(Dppb){sub 2})(PF{sub 6}){sub 2}(C{sub 74}H{sub 64}F{sub 12}NiP{sub 6}) were measured and are reported herein. Calculations made using the extended Huckel theory indicate that the observed distortions may have an electronic as well as a steric component. The calculations also allow rationalization of the electronic absorption spectra, electrochemical data, and the stability of the Ni(I) and Pd(I) complexes (Ni(dppp){sub 2})(BF{sub 4}) (where dppp is 1,3-bis(diphenylphosphino)propane) and (Pd(dppx){sub 2})(BF{sub 4}) (where dppx is {alpha},{alpha}{prime}-bis(diphenylphosphino)-o-xylene). Complexes containing the ligand dppm have a marked tendency to become five-coordinate, as indicated by the structural determination of (Ni(dppm){sub 2}(CH{sub 3}CN))(PF{sub 6}){sub 2}. The crystal structure for the latter complex is reported.« less
  • Two series of mononuclear Ni(II) complexes of the formula (PNP)Ni(dithiolate) where PNP = R2PCH2N(CH3)CH2PR2, R = Et and Ph, have been synthesized containing dithiolate ligands that vary from 5 to 7-membered chelate rings. Two series of dinuclear Ni(II) complexes of the formula {[(diphosphine)Ni]2(dithiolate)}(X)2 (X = BF4 or PF6) have been synthesized in which the chelate ring size of the dithiolate and diphosphine ligands have been systematically varied. The structures of the alkylated mononuclear complex, [(PNPEt)Ni(SC2H4SMe)]OTf and the dinuclear complex [(dppeNi)2(SC3H6S)](BF4)2, have been determined by X-ray diffraction studies. The complexes have been studied by cyclic voltammetry to determine how the Ni(II/I)more » couple varies with chelate ring size of the ligands. A systematic anodic shift in the reduction potential is observed for the mononuclear complexes as the natural bite angle of the dithiolate ligand increases. However the Ni(II/I) couples of the dinuclear complexes do not change systematically as the ligands are varied. Other aspects of the reduction chemistry of these complexes have been explored. This work was supported by the Office of Basic Energy Sciences of the Department of Energy, in part by the Chemical Sciences program and in part by the Engineering and Geosciences Division. The Pacific Northwest National Laboratory is operated by Battelle for the U.S. Department of Energy.« less
  • Nickel(II) bis(diphosphine) complexes that contain positioned bases in the second coordination sphere have been found to catalyze the reduction of O2 with H2 to selectively form water. The complexes also serve as electrocatalysts for the reduction of O2 with the addition of a weak acid. In contrast, a closely related nickel diphosphine complex without the positioned bases is catalytically inactive for O2 reduction. These results indicate that pendant bases in synthetic catalysts for O2 reduction can play a similar role to proton relays in enzymes, and that such relays should be considered in the design of catalysts for multi-electron andmore » multi-proton reactions. This work was supported by the US Department of Energy Basic Energy Sciences' Chemical Sciences, Geosciences & Biosciences Division. Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy.« less
  • The cyclic diphosphine ligands PtBu2NPh2 and PtBu2NBz2 have been synthesized and used to prepare new complexes of Co(II) and Ni(II) with the formula [M(PtBu2NR2)(CH3CN)n](BF4)2 (n = 2, 3). The products have been characterized by variable temperature NMR data, X-ray diffraction studies, and cyclic voltammetry, and properties of the new complexes have been compared with previously studied complexes containing PPh2NR2 ligands. The variation of either phosphorus or nitrogen substituents in these ligands can result in significant differences in the structure, electrochemistry and reactivity of the metal complexes. [Co(PtBu2NPh2)(CH3CN)3](BF4)2 is found to be an effective electrocatalyst for the formation of hydrogen usingmore » bromoanilinium tetrafluoroborate as the acid, with a turnover frequency of 62 s-1 and an overpotential of 160 mV, and these cobalt derivatives are a promising class of catalysts for further study and optimization. This work was supported by the US Department of Energy Basic Energy Sciences' Chemical Sciences, Geosciences & Biosciences Division. Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy. 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.« less
  • Prediction of thermodynamic quantities such as redox potentials and homolytic and heterolytic metal hydrogen bond energies is critical to the a priori design of molecular catalysts. In this paper we expound upon a density functional theory (DFT)-based isodesmic methodology for the accurate computation of the above quantities across a series of Ni(diphosphine)2 complexes compounds that are potential catalysts for production of H2 from protons and electrons, or oxidation of H2 to electrons and protons. Isodesmic schemes give relative free energies between the complex of interest and a reference system. A natural choice is to use as a reference a compoundmore » that shares similarities with the chemical species under study and for which the properties of interest have been measured with accuracy. However, this is not always possible as in the case of the Ni complexes considered here where data are experimentally available for only some species. To overcome this difficulty we employed a theoretical reference compound, Ni(PH3)4, which is amenable to highly accurate electron-correlated calculations, which allows one to explore thermodynamics properties even when no experimental input is accessible. The reliability of this reference is validated against the available thermodynamics data in acetonitrile solution. Overall the proposed protocol yields excellent accuracy for redox potentials (~ 0.10 eV of accuracy), for acidities (~1.5 pKa units of accuracy), for hydricities (~2 kcal/mol of accuracy), and for homolytic bond dissociation free energies (~ 1-2 kcal/mol of accuracy). The calculated thermodynamic properties are then analyzed for a broad set of Ni complexes. The power of the approach is demonstrated through the validation of previously reported linear correlations among properties. New correlations are revealed. It emerges that only two quantities, the Ni(II)/Ni(I) and Ni(I)/Ni(0) redox potentials (which are easily accessible experimentally), suffice to predict with high confidence the energetics of all relevant species involved in the catalytic cycles for H2 oxidation and production. The approach is extendable to other transition metal complexes. 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.« less