A Ni^II–Bis(diphosphine)–Hydride Complex Containing Proton Relays – Structural Characterization and Electrocatalytic Studies

Abstract

The synthesis of the 1,5‐diphenyl‐3,7‐diisopropyl‐1,5‐diaza‐3,7‐diphosphacyclooctane ligand, PiPr2NPh2, is reported. Two equivalents of the ligand react with [Ni(CH3CN)6](BF4)2 to form the bis(diphosphine)–NiII complex [Ni(PiPr2NPh2)2](BF4)2, which acts as a proton reduction electrocatalyst. In addition to [Ni(PiPr2NPh2)2]2+, we report the synthesis and structural characterization of the Ni0 complex Ni(PiPr2NPh2)2 and the NiII–hydride complex [HNi(PiPr2NPh2)2]BF4. The [HNi(PiPr2NPh2)2]BF4 complex represents the first NiII–hydride in the [Ni(PR2NR′2)2]2+ family of compounds to be structurally characterized. In addition to the experimental data, the mechanism of electrocatalysis facilitated by [Ni(PiPr2NPh2)2]2+ is analyzed by using linear free energy relationships recently established for the [Ni(PR2NR′2)2]2+ family.

Incorporation of Pendant Bases into Rh(diphosphine)2 Complexes: Synthesis, Thermodynamic Studies, And Catalytic CO2 Hydrogenation Activity of [Rh(P2N2)2]+ Complexes

“…In this structure, one arm of the P 2 N 2 ligands is also pointed toward the expected location of the hydride ligand as it is in complexes 8 and 9, indicating a possible hydrogen bonding interaction between the pendant amine and hydride ligand. 20 In the case of the nickel complexes, this interaction has also been observed in spectroscopic and computational data. 21 It should be noted that the interaction between the amine arm and the hydride ligand in the crystal structures of complexes 8 and 9 does not necessarily indicate an interaction in solution.…”

Electrode initiated proton-coupled electron transfer to promote degradation of a nickel(ii) coordination complex

“…40 We suggest that this proton–electron reactivity forms a hydride species, a putative intermediate in many catalytic cycles for the Ni-mediated formation of H 2 . 41 – 43 …”

“…40 We suggest that this proton-electron reactivity forms a hydride species, a putative intermediate in many catalytic cycles for the Nimediated formation of H 2 . [41][42][43] Notably, the peak of this irreversible prewave appears ca. 0.28 V positive of the cathodic peak position of the reversible wave of 1 observed in the absence of [Et 3 NH][BF 4 ].…”

Systematic Trends in the Electrochemical Properties of Transition Metal Hydride Complexes Discovered by Using the Ligand Acidity Constant Equation

“…We have uncovered important trends between the estimated p K a LAC ([MHL n ] + /ML n ) for the odd-electron complexes (p K a 2 in Scheme ) and the reversibility or the irreversibility of the corresponding reduction potential E ([MHL n ] + /MHL n ) ( E 1 in Scheme ) by examining the reported electrochemical behavior of hydride complexes from groups 5 to 10. Odd-electron hydride complexes are often implicated in the mechanisms of action of homogeneous electrocatalysts ,,,− and photoelectrocatalysts − for hydrogen production or oxidation and carbon dioxide reduction. Abundant 3 d transition metals are now being used to make active catalysts in the pursuit of more sustainable methods of hydrogen production, storage and utilization. ,,, Reports of the identification of paramagnetic hydrides of 3 d metals as active catalytic species in isomerization, hydrogenase-like action and asymmetric hydrogenation are appearing. − Therefore, the knowledge gained by our study is applicable for the rational design of superior catalysts for these processes.…”