Related Experiment Video
Updated: Apr 1, 2026
![Protein Film Infrared Electrochemistry Demonstrated for Study of H2 Oxidation by a [NiFe] Hydrogenase](/_next/image?url=https%3A%2F%2Fcloudfront.jove.com%2FCDNSource%2Fteasers%2F55858.jpg&w=3840&q=50)
Protein Film Infrared Electrochemistry Demonstrated for Study of H2 Oxidation by a [NiFe] Hydrogenase
Published on: December 4, 2017
Potential-Dependent Electrocatalytic Pathways: Controlling Reactivity with pKa for Mechanistic Investigation of a
Eric S Rountree1, Jillian L Dempsey1
1Department of Chemistry, University of North Carolina , Chapel Hill, North Carolina 27599-3290, United States.
Abstract:
A detailed mechanistic analysis is presented for the hydrogen evolution catalyst [Ni(P2(Ph)N2(Ph))2(CH2CN)][BF4]2 in acetonitrile (P2(Ph)N2(Ph) = 1,3,5,7-tetraphenyl-1,5-diaza-3,7-diphosphacyclooctane). This complex has a Ni(II/I) redox couple at −0.83 V and a Ni(I/0) redox couple at −1.03 V versus Fc(+/0). These two closely spaced redox events both promote proton reduction catalysis, each via a distinct mechanism: an electrochemical ECEC pathway and an EECC route. The EECC mechanism, operative at more negative potentials, was isolated through use of a weak acid (anilinium, pKa = 10.6 in CH3CN) to avert protonation of the singly reduced species. Electroanalytical methods and time-resolved spectroscopy were used to analyze the kinetics of the elementary steps of hydrogen evolution catalysis. The rate constant for the formation of a nickel(II)–hydride intermediate was determined via measurements of peak shift (k1 = 1.2 × 106 M(-1) s(-1)) and through foot-of-the-wave analysis (k1 = 6.5 × 106 M(-1) s(-1)). Reactivity of the isolated hydride with acid to release hydrogen and regenerate the nickel(II) complex was monitored by stopped-flow spectroscopy. Kinetics obtained from stopped-flow measurements are corroborated by current plateau analysis of the catalytic cyclic voltammograms. These kinetic data suggest the presence of an off-cycle intermediate in the reaction.
More Related Videos
Related Concept Videos
Catalysis
Heterogeneous Catalysis
Reduction of Alkenes: Catalytic Hydrogenation
Metals like palladium, platinum, and nickel are commonly used in their solid forms — fine powder on an inert surface. As these catalysts remain insoluble in the reaction mixture, they are referred to as heterogeneous catalysts.
The hydrogenation process takes place on the...
Reduction of Alkenes: Asymmetric Catalytic Hydrogenation
The metal catalyst used can be either heterogeneous or homogeneous. When hydrogenation of an alkene generates a chiral center, a pair of enantiomeric products is expected to form. However, an enantiomeric excess of one of the products can be facilitated using an enantioselective reaction or an...
Processes at Electrodes
Reduction of Alkynes to cis-Alkenes: Catalytic Hydrogenation
Like alkenes, alkynes can be reduced to alkanes in the presence of transition metal catalysts such as Pt, Pd, or Ni. The reaction involves two sequential syn additions of hydrogen via a cis-alkene intermediate.

