Synthesis and characterization of [FeFe]-hydrogenase models with bridging moieties containing (S, Se) and (S, Te)

Mohammad K. Harb, Helmar Görls, Taka Sakamoto, Greg A.N. Felton, Dennis H. Evans, Richard S. Glass, Dennis L. Lichtenberger, Mohammad El-Khateeb, Wolfgang Weigand

Research output: Contribution to journalArticle

22 Scopus citations

Abstract

[FeFe]-hydrogenase-active-site models containing larger chalcogens such as Se or Te have exhibited greater electron richness at the metal centers and smaller gas-phase ionization energies and reorganization energies relative to molecules containing S atoms. Diiron complexes related to the much-studied molecule [Fe2(μ-SC3H6S)(CO)6] (1) have been prepared with one S atom replaced either by one Se atom to give [Fe2(μ-SC3H6Se)(CO)6] (2) or by one Te atom to give [Fe2(μ-SC3H6Te)(CO) 6] (3). The molecules have been characterized by use of mass spectrometry and 13C{1H} NMR, 77Se{ 1H} NMR, IR, and photoelectron spectroscopic techniques along with structure determination with single-crystal X-ray diffraction, electrochemical measurements, and DFT calculations. He I photoelectron spectra and DFT computations of 2 and 3 show a lowering of ionization energies relative to those of the all-sulfur complex 1, indicating increased electron richness at the metal centers that favors electrocatalytic reduction of protons from weak acids to produce H2. However, chalcogen substitution from S to Se or Te also causes an increase in the Fe-Fe bond length, which disfavors the formation of a carbonyl-bridged "rotated" structure, as also shown by the photoelectron spectra and computations. This "rotated" structure is believed to be important in the mechanism of H2 production. As a consequence of the competing influences of increased electron richness at the metals with less favorable "rotated" structures, the catalytic efficiency of the Se and Te molecules 2 and 3 is found to be comparable to that of molecule 1.

Original languageEnglish (US)
Pages (from-to)3976-3985
Number of pages10
JournalEuropean Journal of Inorganic Chemistry
Issue number25
DOIs
StatePublished - Sep 1 2010

Keywords

  • Electrocatalysis
  • Hydrogenases
  • Iron
  • Selenium
  • Sulfur
  • Tellurium

ASJC Scopus subject areas

  • Inorganic Chemistry

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