Electrocatalytic Hydrogen Generation by Ni-PN 3 P Pincer Complexes: Role of Phosphorus Substituents in Tuning the Reactivity

• Published in: Chemistry, an Asian journal Vol. 19; no. 23; p. e202400690
• Main Authors: Chatterjee, Sudipta, Dutta, Indranil, Dereli, Busra, Chakraborty, Priyanka, Peramaiah, Karthik, Gupta, Neha, Cavallo, Luigi, Huang, Kuo-Wei
• Format: Journal Article
• Language: English
• Published: Germany 02.12.2024
• Subjects: Cyclic voltammetry; Electrocatalysis; DFT; Pincer; Hydrogen evolution
• ISSN: 1861-471X
• DOI: 10.1002/asia.202400690

Electrocatalytic hydrogen evolution reaction (eHER) is crucial in addressing the growing global energy demand. Although nickel-pincer-based molecular complexes, varying in donor atoms, were studied previously for eHER, the impact of variations in the substituents attached to the donor atoms was not investigated. Herein, three air-stable PN P -based Ni -pincer complexes [R1=R2=Ph (7); R1=R2= Bu (9); R1= Bu , R2=Ph (10)], varying solely in P-substituents, were studied in acetonitrile. While the redox potentials for Ni and Ni couples underwent anodic shifts by ~100 mV upon progressively substituting tert-butyl by phenyl groups on each P-atom, the corresponding eHER reactivity with organic acids (acetic acid, p-toluenesulfonic acid and trifluoromethanesulfonic acid) of different strengths followed different trends; likely influenced by the pK of intermediate metal-hydride (M-H) species [pKa(M-H )>pKa(M-H )>pKa(M-H )]. Depending on the acid strength, different oxidation states of the metal were activated to promote eHER. The catalytic rates for 9, 10, and 7 were calculated to be 85 s , 77 s and 95 s with Faradaic efficiencies of 88.5±2 %, 66.1±1.4 %, and 91.7±1.5 % respectively, in acetic acid. Electrochemical data supported by theoretical results reinforce a significant electronic influence of the anchoring P-substituents on the activity of these complexes.