Mixed-Valence Nickel-Iron Dithiolate Models of the [NiFe]-Hydrogenase Active Site

作者：Schilter David; Nilges Mark J; Chakrabarti Mrinmoy; Lindahl Paul A^*; Rauchfuss Thomas B; Stein Matthias

来源：Inorganic Chemistry, 2012, 51(4): 2338-2348.

DOI：10.1021/ic202329y

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 = Ph2PCH2CH2PPh2, dcpe = Cy2PCH2CH2PCy2, (Cy = cyclohexyl), pdtH(2) = HSCH2CH2CH2SH, and edtH(2) = HSCH2CH2SH. The cation [2](+) proved unstable, but the propanedithiolates are robust. IR and EPR spectroscopic measurements indicate that these species exist as C-s-symmetric species. Crystallographic characterization of [3]BF4 shows that Ni is square planar. Interaction of [1]BF4 with P-donor ligands (L) afforded a series of substituted derivatives of type [(dppe)Ni(pdt)Fe(CO)(2)L]BF4 for L = P(OPh)(3) ([4a]BF4), P(p-C6H4Cl)(3) ([4b]BF4), PPh2(2-py) ([4c]BF4), PPh2(OEt) ([4d]F-4), PPh3 ([4e]BF4), PPh2-(o-C6H4OMe) ([4f]BF4), PPh2(o-C6H4OCH2OMe) ([4g]BF4), P(p-tol)(3) ([4h]BF4), P(p-C6H4OMe)(3) ([4i]BF4), and PMePh2 ([4j]BF4). 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. Mossbauer spectra of 1 and oxidized S = 1/2 [4e]BF4 are both consistent with a low-spin Fe(I) state. The hyperfine coupling tensor of [4e]BF4 has a small isotropic component and significant anisotropy. DFT calculations using the BP86, B3LYP, and PBEO 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(z(2)) 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.

• 出版日期2012-2-20