Mixed-valence nickel-iron dithiolate models of the [NiFe]-hydrogenase active site

David Schilter, Mark J. Nilges, Mrinmoy Chakrabarti, Paul A. Lindahl, Thomas B. Rauchfuss, Matthias Stein

Research output: Contribution to journalArticlepeer-review


A series of mixed-valence nickel-iron dithiolates is described. Oxidation of (diphosphine)Ni(dithiolate)Fe(CO) 3 complexes 1, 2, and 3 with ferrocenium salts affords the corresponding tricarbonyl cations [(dppe)Ni(pdt)Fe-(CO) 3] + ([1] +), [(dppe)Ni(edt)Fe(CO) 3] + ([2] +)and [(dcpe)Ni(pdt)Fe(CO) 3] + ([3] +), respectively, where dppe = PH 2PCH 2CH 2PPH 2, dcpe = Cy 2PCH 2CH 2PCy 2, (Cy = cyclohexyl), pdtH 2 = HSCH 2CH 2CH 2SH, and edtH 2 = HSCH 2CH 2SH. The cation [2] + proved unstable, but the propanedithiolates are robust. IR and EPR spectroscopic measurements indicate that these species exist as Cs-symmetric species. Crystallographic characterization of [3]BF 4 shows that Ni is square planar. Interaction of [1]BF 4 with P-donor ligands (L)afforded a series of substituted derivatives of type [(dppe)Ni(pdt)Fe(CO) 2L]BF 4 for L = P(OPh) 3 ([4a]BF 4), P(p-C 6H 4Cl) 3 ([4b]BF 4), PPH 2(2-py)([4c]BF 4), PPH 2(OEt)([4d]BF 4), PPh 3 ([4e]BF 4), PPH 2-(o-C 6H 4OMe)([4f]BF 4), PPH 2(o-C 6H 4OCH 2OMe)([4g]BF 4), P(p-tol) 3 ([4h]BF 4), P(p-C 6H 4OMe) 3 ([4i]BF 4), and PMePH 2 ([4j]BF 4). EPR analysis indicates that ethanedithiolate [2] + exists as a single species at 110 K, whereas the propanedithiolate cations exist as a mixture of two conformers, which are proposed to be related through a flip of the chelate ring. Mössbauer spectra of 1 and oxidized S = 1/2 [4e]BF 4 are both consistent with a low-spin Fe(I)state. The hyperfine coupling tensor of [4e]BF 4 has a small isotropic component and significant anisotropy. DFT calculations using the BP86, B3LYP, and PBE0 exchange-correlation functionals agree with the structural and spectroscopic data, suggesting that the SOMOs in complexes of the present type are localized in an Fe(I)-centered d(z2)orbital. The DFT calculations allow an assignment of oxidation states of the metals and rationalization of the conformers detected by EPR spectroscopy. Treatment of [1] + with CN-and compact basic phosphines results in complex reactions. With dppe, [1] + undergoes quasi-disproportionation to give 1 and the diamagnetic complex [(dppe)Ni(pdt)Fe(CO) 2(dppe)] 2+ ([5] 2+), which features square-planar Ni linked to an octahedral Fe center.

Original languageEnglish (US)
Pages (from-to)2338-2348
Number of pages11
JournalInorganic Chemistry
Issue number4
StatePublished - Feb 20 2012

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry


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