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

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

Research output: Contribution to journalArticle

12 Citations (Scopus)

Abstract

A new Ni(II) complex, [Ni(7PPh 2NH)2H]3+ (7PPh 2NH = 3,6-diphenyl-1-aza-3,6-diphosphacycloheptane), has been synthesized, and its electrochemical properties have been reported. The 7PPh 2NH 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(PPh 2NR′ 2)2]2+ (PPh 2NR′ 2 = 3,7-diphenyl-1,5-diaza-3,7-diphosphacyclooctane) and other [Ni(7PPh 2NR′)2]2+ complexes, catalytic turnover frequencies for H2 production by [Ni(7PPh 2NH)2]2+ do not show catalytic rate enhancement upon the addition of H2O. This finding supports the assertion that [Ni(7PPh 2NH)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

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Protonation
Hydrogen production
Electrocatalysis
Electrocatalysts
Organic acids
Electrochemical properties
Isomers
Amines
Metals
Ligands
diphenyl

Keywords

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

ASJC Scopus subject areas

  • Catalysis

Cite this

Electrocatalytic hydrogen production by [Ni(7PPh 2NH)2]2+ : Removing the Distinction between endo- and exo-protonation sites. / Brown, Houston J S; Wiese, Stefan; Roberts, John; Bullock, R Morris; Helm, Monte.

In: ACS Catalysis, Vol. 5, No. 4, 03.04.2015, p. 2116-2123.

Research output: Contribution to journalArticle

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N2 - A new Ni(II) complex, [Ni(7PPh 2NH)2H]3+ (7PPh 2NH = 3,6-diphenyl-1-aza-3,6-diphosphacycloheptane), has been synthesized, and its electrochemical properties have been reported. The 7PPh 2NH 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(PPh 2NR′ 2)2]2+ (PPh 2NR′ 2 = 3,7-diphenyl-1,5-diaza-3,7-diphosphacyclooctane) and other [Ni(7PPh 2NR′)2]2+ complexes, catalytic turnover frequencies for H2 production by [Ni(7PPh 2NH)2]2+ do not show catalytic rate enhancement upon the addition of H2O. This finding supports the assertion that [Ni(7PPh 2NH)2]2+ eliminates the distinction between the endo- and exo-protonation isomers.

AB - A new Ni(II) complex, [Ni(7PPh 2NH)2H]3+ (7PPh 2NH = 3,6-diphenyl-1-aza-3,6-diphosphacycloheptane), has been synthesized, and its electrochemical properties have been reported. The 7PPh 2NH 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(PPh 2NR′ 2)2]2+ (PPh 2NR′ 2 = 3,7-diphenyl-1,5-diaza-3,7-diphosphacyclooctane) and other [Ni(7PPh 2NR′)2]2+ complexes, catalytic turnover frequencies for H2 production by [Ni(7PPh 2NH)2]2+ do not show catalytic rate enhancement upon the addition of H2O. This finding supports the assertion that [Ni(7PPh 2NH)2]2+ eliminates the distinction between the endo- and exo-protonation isomers.

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