Interconversion of Formic Acid and Carbon Dioxide by Proton-Responsive, Half-Sandwich CpIrIII Complexes: A Computational Mechanistic Investigation

Mehmed Z. Ertem, Yuichiro Himeda, Etsuko Fujita, James Muckerman

Research output: Contribution to journalArticle

44 Citations (Scopus)

Abstract

Dihydrogen (H2) has many desirable features as a fuel, but utilization of H2 is limited due to storage and transportation problems. A promising solution to these issues is reversible storage of hydrogen in the form of liquid-phase chemicals such as formic acid (FA), which could be accomplished by the development of efficient and robust catalysts. Recently, proton-responsive, half-sandwich CpIrIII (where Cp∗ = pentamethylcyclopentadienyl anion) complexes capable of reversible hydrogen storage via interconversion between H2/CO2 and formic acid/formate in water have been reported. This interconversion is performed via CO2 hydrogenation and FA dehydrogenation reactions and modulated by the pH of the medium. We report the results of a computational investigation of the mechanistic aspects of reversible hydrogen storage via two of these catalysts: namely, [CpIr(4DHBP)]2+ (4DHBP = 4,4′-dihydroxy-2,2′-bipyridine) and [CpIr(6DHBP)]2+ (6DHBP = 6,6′-dihydroxy-2,2′-bipyridine). Distinct features of the catalytic cycles of [CpIr(4DHBP)]2+ and [CpIr(6DHBP)]2+ for CO2 hydrogenation and FA dehydrogenation reactions are demonstrated using density functional theory (DFT) calculations employing a speciation approach and probing deuterium kinetic isotope effects (KIE). In addition to the mechanistic insights and principles for the design of improved next-generation catalysts, the validation of computational methods for the investigation of the hydrogenation and dehydrogenation reactions is addressed.

Original languageEnglish
Pages (from-to)600-609
Number of pages10
JournalACS Catalysis
Volume6
Issue number2
DOIs
Publication statusPublished - Feb 5 2016

Keywords

  • CO hydrogenation
  • density functional theory
  • formic acid dehydrogenation
  • hydrogen storage
  • iridium complexes
  • kinetic isotope effect
  • proton-responsive ligand

ASJC Scopus subject areas

  • Catalysis

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