Highly Robust Hydrogen Generation by Bioinspired Ir Complexes for Dehydrogenation of Formic Acid in Water: Experimental and Theoretical Mechanistic Investigations at Different pH

Wan Hui Wang, Mehmed Z. Ertem, Shaoan Xu, Naoya Onishi, Yuichi Manaka, Yuki Suna, Hide Kambayashi, James T. Muckerman, Etsuko Fujita, Yuichiro Himeda

Research output: Contribution to journalArticle

86 Citations (Scopus)

Abstract

Hydrogen generation from formic acid (FA), one of the most promising hydrogen storage materials, has attracted much attention due to the demand for the development of renewable energy carriers. Catalytic dehydrogenation of FA in an efficient and green manner remains challenging. Here, we report a series of bioinspired Ir complexes for highly robust and selective hydrogen production from FA in aqueous solutions without organic solvents or additives. One of these complexes bearing an imidazoline moiety (complex 6) achieved a turnover frequency (TOF) of 322 000 h-1 at 100 °C, which is higher than ever reported. The novel catalysts are very stable and applicable in highly concentrated FA. For instance, complex 3 (1 μmol) affords an unprecedented turnover number (TON) of 2 050 000 at 60 °C. Deuterium kinetic isotope effect experiments and density functional theory (DFT) calculations employing a "speciation" approach demonstrated a change in the rate-determining step with increasing solution pH. This study provides not only more insight into the mechanism of dehydrogenation of FA but also offers a new principle for the design of effective homogeneous organometallic catalysts for H2 generation from FA.

Original languageEnglish
Pages (from-to)5496-5504
Number of pages9
JournalACS Catalysis
Volume5
Issue number9
DOIs
Publication statusPublished - Jul 30 2015

Keywords

  • Ir complexes
  • formic acid dehydrogenation
  • kinetic isotope effect
  • mechanism
  • pH dependence

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)

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