Electrocatalytic Hydrogen Generation by Ni‐PN3P Pincer Complexes: Role of Phosphorus Substituents in Tuning the Reactivity

Electrocatalytic hydrogen evolution reaction ( e HER) is crucial in addressing the growing global energy demand. Although nickel‐pincer‐based molecular complexes, varying in donor atoms, were studied previously for e HER, the impact of variations in the substituents attached to the donor atoms was not investigated. Herein, three air‐stable R1 PN 3 P R2 ‐based Ni II –pincer complexes [R1=R2=Ph 2 ( 7 ); R1=R2= t Bu 2 ( 9 ); R1= t Bu 2 , R2=Ph 2 ( 10 )], varying solely in P‐substituents, were studied in acetonitrile. While the redox potentials for Ni II/I and Ni I/0 couples underwent anodic shifts by ~100 mV upon progressively substituting tert ‐butyl by phenyl groups on each P‐atom, the corresponding e HER reactivity with organic acids (acetic acid, p‐toluenesulfonic acid and trifluoromethanesulfonic acid) of different strengths followed different trends; likely influenced by the p K a of intermediate metal‐hydride (M–H) species [p K a(M–H 9 )>p K a(M–H 10 )>p K a(M–H 7 )]. Depending on the acid strength, different oxidation states of the metal were activated to promote e HER. The catalytic rates for 9 , 10 , and 7 were calculated to be 85 s −1 , 77 s −1 and 95 s −1 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.