The role of pendant amines in the breaking and forming of molecular hydrogen catalyzed by nickel complexes

Simone Raugei, Shentan Chen, Ming Hsun Ho, Bojana Ginovska-Pangovska, Roger J. Rousseau, Michel Dupuis, Daniel L. Dubois, R. Morris Bullock

Research output: Contribution to journalArticle

84 Citations (Scopus)

Abstract

We present the results of a comprehensive theoretical investigation of the role of pendant amine ligands in the oxidation of H 2 and formation of H 2 by [Ni(P R 2N R' 2) 2] 2+ electrocatalysts (P R 2N R' 2 is the 1,5-R'-3,7-R derivative of 1,5-diaza-3,7- diphosphacyclooctane, in which R and R' are aryl or alkyl groups). We focus our analysis on the thermal steps of the catalytic cycle, as they are known to be rate-determining for both H 2 oxidation and production. We find that the presence of pendant amine functional groups greatly facilitates the heterolytic H 2 bond cleavage, resulting in a protonated amine and a Ni hydride. Only one single positioned pendant amine is required to serve this function. The pendant amine can also effectively shuttle protons to the active site, making the redistribution of protons and the H 2 evolution a very facile process. An important requirement for the overall catalytic process is the positioning of at least one amine in close proximity to the metal center. Indeed, only protonation of the pendant amines on the metal center side (endo position) leads to catalytically active intermediates, whereas protonation on the opposite side of the metal center (exo position) leads to a variety of isomers, which are detrimental to catalysis.

Original languageEnglish
Pages (from-to)6493-6506
Number of pages14
JournalChemistry - A European Journal
Volume18
Issue number21
DOIs
Publication statusPublished - May 21 2012

Keywords

  • amines
  • density functional calculations
  • homogeneous catalysis
  • hydrogen
  • nickel
  • reaction mechanisms

ASJC Scopus subject areas

  • Catalysis
  • Organic Chemistry

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