Interplay between β-Diimino and β-Diketiminato Ligands in Nickel Complexes Active in the Proton Reduction Reaction

Abstract

Two Ni complexes are reported with κ4-P2N2 β-diimino (BDI) ligands with the general formula [Ni­(XBDI)]­(BF4)2, where BDI is N-(2-(diphenylphosphaneyl)­ethyl)-4-((2-(diphenylphosphaneyl)­ethyl)­imino)­pent-2-en-2-amine and X indicates the substituent in the α-carbon intradiimine position, X = H for 1(BF4)2 and X = Ph for 2(BF4)2. Electrochemical analysis together with UV–vis and NMR spectroscopy in acetonitrile and dimethylformamide (DMF) indicates the conversion of the β-diimino complexes 12+ and 22+ to the negatively charged β-diketiminato (BDK) analogues (1-H)+ and (2-H)+ via deprotonation in DMF. Moreover, further electrochemical and spectroscopy evidence indicates that the one-electron-reduced derivatives 1+ and 2+ can also rapidly evolve to the BDK (1-H)+ and (2-H)+, respectively, via hydrogen gas evolution through a bimolecular homolytic pathway. Finally, both complexes are demonstrated to be active for the proton reduction reaction in DMF at E app = −1.8 V vs Fc+/0, being the active species the one-electron-reduced derivative 1-H and 2-H.

Electrocatalytic Hydrogen Evolution using a Nickel‐based Calixpyrrole Complex: Controlling the Secondary Coordination Sphere on an Electrode Surface

“…Efforts to isolate catalytic intermediates, as well as to independently synthesize partially reduced nickel calixpyrrole complexes are currently underway. Furthermore, it should be noted that hydrogen evolution pathways that invoke a Ni III ‐hydride cannot be ruled out at this time [85–89] …”

“…Furthermore, it should be noted that hydrogen evolution pathways that invoke a Ni III -hydride cannot be ruled out at this time. [85][86][87][88][89]…”

Revealing the Mechanistic Features of an Electrosynthetic Catalytic Reaction and the Role of Redox Mediators through DFT Calculations and Microkinetic Modeling

“…A wide range of overpotential values have been reported between 0.01 and 1.0 V, and our estimation fits well within these margins. [42][43][44][45] We took this estimated value of 0.540 V for overpotential, and applied it to the main experiment, which was carried out under galvanostatic conditions. We concluded that the applied potential had to be 0.820 V, and this produced a reaction yield of 89 %, which is very close to the experimental result which is 86 % isolated yield.…”

Kappa what? Insights into the coordination modes of N2P2 ligands

“…Most recently, the conversion between β-Diimino and β-Diketiminato ligands ( 30 ) was reported for two Ni( ii ) N 2 P 2 complexes. 73 Upon reaction with Ni(BF 4 ) 2 ·6H 2 O, the β-Diketiminato ligand was converted to a square planar Ni( ii ) β-Diimino complex with two tetrafluoroborate anions. The Ni( ii ) β-Diketiminato complex can be accessed from the Ni( ii ) β-Diimino complex in the presence of a very weak base such as DMF due to the increased acidity of the α-CH proton upon metalation.…”