Studies of a Series of [Ni(P<sup>R</sup><sub>2</sub>N<sup>Ph</sup><sub>2</sub>)<sub>2</sub>(CH<sub>3</sub>CN)]<sup>2+</sup> Complexes as Electrocatalysts for H<sub>2</sub> Production: Substituent Variation at the Phosphorus Atom of the P<sub>2</sub>N<sub>2</sub> Ligand Uriah J. Kilgore Michael P. Stewart Monte L. Helm William G. Dougherty W. Scott Kassel Mary Rakowski DuBois Daniel L. DuBois R. Morris Bullock 10.1021/ic201461a.s002 https://acs.figshare.com/articles/dataset/Studies_of_a_Series_of_Ni_P_sup_R_sup_sub_2_sub_N_sup_Ph_sup_sub_2_sub_sub_2_sub_CH_sub_3_sub_CN_sup_2_sup_Complexes_as_Electrocatalysts_for_H_sub_2_sub_Production_Substituent_Variation_at_the_Phosphorus_Atom_of_the_P_sub_2_sub_N_sub_2_sub_Ligand/2588545 A series of [Ni(P<sup>R</sup><sub>2</sub>N<sup>Ph</sup><sub>2</sub>)<sub>2</sub>(CH<sub>3</sub>CN)](BF<sub>4</sub>)<sub>2</sub> complexes containing the cyclic diphosphine ligands [P<sup>R</sup><sub>2</sub>N<sup>Ph</sup><sub>2</sub> = 1,5-diaza-3,7-diphosphacyclooctane; R = benzyl (Bn), <i>n</i>-butyl (<i>n-</i>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(P<sup>Bn</sup><sub>2</sub>N<sup>Ph</sup><sub>2</sub>)<sub>2</sub>(CH<sub>3</sub>CN)](BF<sub>4</sub>)<sub>2</sub> and [Ni(P<sup><i>n</i>‑Bu</sup><sub>2</sub>N<sup>Ph</sup><sub>2</sub>)<sub>2</sub>(CH<sub>3</sub>CN)](BF<sub>4</sub>)<sub>2</sub> have distorted trigonal bipyramidal geometries. The Ni(0) complex [Ni(P<sup>Bn</sup><sub>2</sub>N<sup>Ph</sup><sub>2</sub>)<sub>2</sub>] 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(P<sup>Cy</sup><sub>2</sub>N<sup>Ph</sup><sub>2</sub>)<sub>2</sub>(CH<sub>3</sub>CN)](BF<sub>4</sub>)<sub>2</sub>, all exhibit reversible electron transfer processes for both the Ni(II/I) and Ni(I/0) couples and are electrocatalysts for the production of H<sub>2</sub> in acidic acetonitrile solutions. The heterolytic cleavage of H<sub>2</sub> by [Ni(P<sup>R</sup><sub>2</sub>N<sup>Ph</sup><sub>2</sub>)<sub>2</sub>(CH<sub>3</sub>CN)](BF<sub>4</sub>)<sub>2</sub> complexes in the presence of <i>p</i>-anisidine or <i>p</i>-bromoaniline was used to determine the hydride donor abilities of the corresponding [HNi(P<sup>R</sup><sub>2</sub>N<sup>Ph</sup><sub>2</sub>)<sub>2</sub>](BF<sub>4</sub>) complexes. However, for the catalysts with the most bulky R groups, the turnover frequencies do not parallel the driving force for elimination of H<sub>2</sub>, 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. 2016-02-22 16:50:54 electron transfer processes hydride donor abilities P 2N LigandA series PR PE Ni H 2 H 2 Production cyclic diphosphine ligands acidic acetonitrile solutions TP complex