Models of the Ni-L and Ni-SIa States of the [NiFe]-Hydrogenase Active Site

Geoffrey M. Chambers, Mioy T. Huynh, Yulong Li, Sharon Hammes-Schiffer, Thomas B. Rauchfuss, Edward Reijerse, Wolfgang Lubitz

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A new class of synthetic models for the active site of [NiFe]-hydrogenases are described. The NiI/II(SCys)2 and FeII(CN)2CO sites are represented with (RC5H4)NiI/II and FeII(diphos)(CO) modules, where diphos = 1,2-C2H4(PPh2)2(dppe) or cis-1,2-C2H2(PPh2)2(dppv). The two bridging thiolate ligands are represented by CH2(CH2S)22- (pdt2-), Me2C(CH2S)22- (Me2pdt2-), and (C6H5S)22-. The reaction of Fe(pdt)(CO)2(dppe) and [(C5H5)3Ni2]BF4 affords [(C5H5)Ni(pdt)Fe(dppe)(CO)]BF4 ([1a]BF4). Monocarbonyl [1a]BF4 features an S = 0 NiIIFeII center with five-coordinated iron, as proposed for the Ni-SIa state of the enzyme. One-electron reduction of [1a]+ affords the S = 1/2 derivative [1a]0, which, according to density functional theory (DFT) calculations and electron paramagnetic resonance and Mössbauer spectroscopies, is best described as a NiIFeII compound. The NiIFeII assignment matches that for the Ni-L state in [NiFe]-hydrogenase, unlike recently reported NiIIFeI-based models. Compound [1a]0 reacts with strong acids to liberate 0.5 equiv of H2 and regenerate [1a]+, indicating that H2 evolution is catalyzed by [1a]0. DFT calculations were used to investigate the pathway for H2 evolution and revealed that the mechanism can proceed through two isomers of [1a]0 that differ in the stereochemistry of the Fe(dppe)CO center. Calculations suggest that protonation of [1a]0 (both isomers) affords NiIII-H-FeII intermediates, which represent mimics of the Ni-C state of the enzyme.

Original languageEnglish (US)
Pages (from-to)419-431
Number of pages13
JournalInorganic Chemistry
Issue number2
StatePublished - Jan 19 2016
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry


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