Electrocatalytic hydrogen production by [Ni(7PPh2NH)2]2+: Removing the Distinction between endo- and exo-protonation sites

Houston J.S. Brown, Stefan Wiese, John A.S. Roberts, R. Morris Bullock, Monte L. Helm

Research output: Contribution to journalArticle

14 Citations (Scopus)

Abstract

A new Ni(II) complex, [Ni(7PPh2NH)2H]3+ (7PPh2NH = 3,6-diphenyl-1-aza-3,6-diphosphacycloheptane), has been synthesized, and its electrochemical properties have been reported. The 7PPh2NH ligand features an NH, ensuring properly positioned protonated amine groups (N-H+) for electrocatalysis, regardless of whether protonation occurs exo or endo to the metal center. The compound is an electrocatalyst for H2 production in the presence of organic acids (pKa range 10-13 in CH3CN), with turnover frequencies ranging from 160 to 780 s-1 at overpotentials between 320 and 470 mV, as measured at the potential of the catalytic wave. In stark contrast to [Ni(PPh2NR′2)2]2+ (PPh2NR′2 = 3,7-diphenyl-1,5-diaza-3,7-diphosphacyclooctane) and other [Ni(7PPh2NR′)2]2+ complexes, catalytic turnover frequencies for H2 production by [Ni(7PPh2NH)2]2+ do not show catalytic rate enhancement upon the addition of H2O. This finding supports the assertion that [Ni(7PPh2NH)2]2+ eliminates the distinction between the endo- and exo-protonation isomers.

Original languageEnglish
Pages (from-to)2116-2123
Number of pages8
JournalACS Catalysis
Volume5
Issue number4
DOIs
Publication statusPublished - Apr 3 2015

Keywords

  • electrocatalysis
  • hydrogen production
  • nickel complexes
  • nickel phosphine complexes
  • pendant amines
  • proton relays

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)

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