Base-free non-noble-metal-catalyzed hydrogen generation from formic acid: Scope and mechanistic insights

Dörthe Mellmann, Enrico Barsch, Matthias Bauer, Kathleen Grabow, Albert Boddien, Anja Kammer, Peter Sponholz, Ursula Bentrup, Ralf Jackstell, Henrik Junge, Gábor Laurenczy, Ralf Ludwig, Matthias Beller

Research output: Contribution to journalArticlepeer-review

53 Scopus citations

Abstract

The iron-catalyzed dehydrogenation of formic acid has been studied both experimentally and mechanistically. The most active catalysts were generated in situ from cationic FeII/FeIII precursors and tris[2-(diphenylphosphino)ethyl]phosphine (1, PP3). In contrast to most known noble-metal catalysts used for this transformation, no additional base was necessary. The activity of the iron catalyst depended highly on the solvent used, the presence of halide ions, the water content, and the ligand-to-metal ratio. The optimal catalytic performance was achieved by using [FeH(PP3)]BF4/PP3 in propylene carbonate in the presence of traces of water. With the exception of fluoride, the presence of halide ions in solution inhibited the catalytic activity. IR, Raman, UV/Vis, and EXAFS/XANES analyses gave detailed insights into the mechanism of hydrogen generation from formic acid at low temperature, supported by DFT calculations. In situ transmission FTIR measurements revealed the formation of an active iron formate species by the band observed at 1543 cm-1, which could be correlated with the evolution of gas. This active species was deactivated in the presence of chloride ions due to the formation of a chloro species (UV/Vis, Raman, IR, and XAS). In addition, XAS measurements demonstrated the importance of the solvent for the coordination of the PP3 ligand.

Original languageEnglish
Pages (from-to)13589-13602
Number of pages14
JournalChemistry - A European Journal
Volume20
Issue number42
DOIs
StatePublished - 1 Oct 2014
Externally publishedYes

Keywords

  • IR spectroscopy
  • dehydrogenation
  • density functional calculations
  • homogeneous catalysis
  • iron
  • reaction mechanisms

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