A series of [Ni(PR2NPh2) 2(CH3CN)](BF4)2 complexes containing the cyclic diphosphine ligands [PR2NPh 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(PBn2NPh2) 2(CH3CN)](BF4)2 and [Ni(P n-Bu2NPh2)2(CH 3CN)](BF4)2 have distorted trigonal bipyramidal geometries. The Ni(0) complex [Ni(PBn2NPh 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(PCy2N Ph2)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(PR2NPh2) 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(PR2N Ph2)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.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry