Studies of a Series of [Ni(PR 2NPh 2)2(CH3CN)]2+ Complexes as Electrocatalysts for H2 Production: Substituent Variation at the Phosphorus Atom of the P2N2 Ligand

A series of [Ni(PR 2NPh 2)2(CH3CN)](BF4)2 complexes containing the cyclic diphosphine ligands [PR 2NPh 2 = 1,5-diaza-3,7-diphosphacyclooctane; R = benzyl (Bn), n-butyl (n-Bu), 2-phenylethyl (PE), 2,4,4-trimethylpentyl (TP), and cyclohexyl (Cy)] have been synthesized and characterized. X-ray diffract...

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Bibliographic Details
Published in:Inorganic chemistry 2011-11, Vol.50 (21), p.10908-10918
Main Authors: Kilgore, Uriah J, Stewart, Michael P, Helm, Monte L, Dougherty, William G, Kassel, W. Scott, DuBois, Mary Rakowski, DuBois, Daniel L, Bullock, R. Morris
Format: Article
Language:English
Subjects:
ACETONITRILE
AMINES
ATOMS
catalysis
CATIONS
CLEAVAGE
ELECTROCATALYSTS
ELECTRON TRANSFER
HYDRIDES
hydrogen
INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY
NITROGEN
PHOSPHORUS
PRODUCTION
X-RAY DIFFRACTION
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Summary:A series of [Ni(PR 2NPh 2)2(CH3CN)](BF4)2 complexes containing the cyclic diphosphine ligands [PR 2NPh 2 = 1,5-diaza-3,7-diphosphacyclooctane; R = benzyl (Bn), n-butyl (n-Bu), 2-phenylethyl (PE), 2,4,4-trimethylpentyl (TP), and cyclohexyl (Cy)] have been synthesized and characterized. X-ray diffraction studies reveal that the cations of [Ni(PBn 2NPh 2)2(CH3CN)](BF4)2 and [Ni(P n‑Bu 2NPh 2)2(CH3CN)](BF4)2 have distorted trigonal bipyramidal geometries. The Ni(0) complex [Ni(PBn 2NPh 2)2] was also synthesized and characterized by X-ray diffraction studies and shown to have a distorted tetrahedral structure. These complexes, with the exception of [Ni(PCy 2NPh 2)2(CH3CN)](BF4)2, all exhibit reversible electron transfer processes for both the Ni(II/I) and Ni(I/0) couples and are electrocatalysts for the production of H2 in acidic acetonitrile solutions. The heterolytic cleavage of H2 by [Ni(PR 2NPh 2)2(CH3CN)](BF4)2 complexes in the presence of p-anisidine or p-bromoaniline was used to determine the hydride donor abilities of the corresponding [HNi(PR 2NPh 2)2](BF4) complexes. However, for the catalysts with the most bulky R groups, the turnover frequencies do not parallel the driving force for elimination of H2, suggesting that steric interactions between the alkyl substituents on phosphorus and the nitrogen atom of the pendant amines play an important role in determining the overall catalytic rate.
ISSN:0020-1669
1520-510X
DOI:10.1021/ic201461a