Electrocatalytic Hydrogen Production by a Nickel Complex Containing a Tetradentate Phosphine Ligand

Christina M. Klug, William G. Dougherty, W. Scott Kassel, Eric Wiedner

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Abstract

A nickel complex has been synthesized using the P4N2 ligand, a tetradentate phosphine ligand with two pendant amines in the ligand backbone. The rigidly square pyramidal [Ni(P4N2)(CH3CN)]2+ complex is an electrocatalyst for the reduction of protons to hydrogen. Using N,N-dimethylformamidium ([DMF(H)+]) as the acid in an acetonitrile/water solution, [Ni(P4N2)(CH3CN)]2+ displays a turnover frequency of 1.6 × 106 s-1, which is among the fastest rates reported for any molecular electrocatalyst. This high catalytic rate comes at the cost of a 1200 mV overpotential at the catalytic half-wave potential. The Ni(II) state of the catalyst was found to be stable under strongly acidic conditions, with only trace decomposition observed over 2 weeks in the presence of 0.1 M trifluoromethanesulfonic acid (HOTf). The catalyst was less stable in the Ni(0) state due to the inability of the rigid P4N2 ligand to adopt a tetrahedral geometry. Using variable scan rate cyclic voltammetry, a first-order rate constant of ∼1 s-1 was measured for dissociation of a phosphine from Ni(0), which is proposed to be a key step for determining the lifetime of the catalyst during electrolysis.

Original languageEnglish
JournalOrganometallics
DOIs
Publication statusAccepted/In press - Jan 1 2018

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ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Organic Chemistry
  • Inorganic Chemistry

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