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Nickel-iron dithiolato hydrides relevant to the [NiFe]-hydrogenase active site.

ABSTRACT: The ferrous dithiolato carbonyl Fe(S(2)C(3)H(6))(CO)(2)(dppe) (1) condenses with NiCl(2)(dppe) to give [FeNi(pdt)(mu-Cl)(CO)(dppe)(2)]BF(4) ([2Cl](+)). The corresponding reaction of the ditosylate Ni(OTs)(2)(dppe) gave the dication [(CO)(2)(dppe)Fe(pdt)Ni(dppe)](OTs)(2) ([2(CO)](OTs)(2)) (pdt = 1,3-propanedithiolate; dppe = 1,2-C(2)H(4)(PPh(2))(2); OTs(-) = CH(3)C(6)H(4)-4-SO(3)(-)). Reduction of the bimetallic dicarbonyl with borohydride salts afforded impure, thermally stable hydride, [(CO)(dppe)Fe(pdt)(mu-H)Ni(dppe)](+) ([2H](+)). A reliable route to NiFe(SR)(2)H species entailed protonation of (CO)(3)Fe(pdt)Ni(dppe) to give [(CO)(3)Fe(pdt)(mu-H)Ni(dppe)](+) ([3H](+)). The iron-nickel dithiolato hydride, [3H]BF(4), was characterized crystallographically: as anticipated by biophysical studies, the hydride ligand is bridging, the Fe center is octahedral, and the Ni center is pentacoordinate. Solutions of [3H]BF(4) undergo substitution by dppe to give [2H](+). The hydride undergoes rapid deprotonation and is an electrocatalyst for hydrogen evolution from trifluoroacetic acid. Oxidation of 3 gives a mixed valence species [3](+), a potential model for the Ni-L state.

SUBMITTER: Barton BE

PROVIDER: S-EPMC4364603 | biostudies-literature | 2009 May

REPOSITORIES: biostudies-literature

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Nickel-iron dithiolato hydrides relevant to the [NiFe]-hydrogenase active site.

Barton Bryan E BE Whaley C Matthew CM Rauchfuss Thomas B TB Gray Danielle L DL

Journal of the American Chemical Society 20090501 20

The ferrous dithiolato carbonyl Fe(S(2)C(3)H(6))(CO)(2)(dppe) (1) condenses with NiCl(2)(dppe) to give [FeNi(pdt)(mu-Cl)(CO)(dppe)(2)]BF(4) ([2Cl](+)). The corresponding reaction of the ditosylate Ni(OTs)(2)(dppe) gave the dication [(CO)(2)(dppe)Fe(pdt)Ni(dppe)](OTs)(2) ([2(CO)](OTs)(2)) (pdt = 1,3-propanedithiolate; dppe = 1,2-C(2)H(4)(PPh(2))(2); OTs(-) = CH(3)C(6)H(4)-4-SO(3)(-)). Reduction of the bimetallic dicarbonyl with borohydride salts afforded impure, thermally stable hydride, [(CO)(dp ...[more]

PMID: 19413314

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Project description: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(2)PCH(2)CH(2)PPh(2), dcpe = Cy(2)PCH(2)CH(2)PCy(2), (Cy = cyclohexyl), pdtH(2) = HSCH(2)CH(2)CH(2)SH, and edtH(2) = HSCH(2)CH(2)SH. 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]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)(2)L]BF(4) for L = P(OPh)(3) ([4a]BF(4)), P(p-C(6)H(4)Cl)(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(6)H(4)OMe) ([4f]BF(4)), PPh(2)(o-C(6)H(4)OCH(2)OMe) ([4g]BF(4)), P(p-tol)(3) ([4h]BF(4)), P(p-C(6)H(4)OMe)(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(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.

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Nickel-iron dithiolato hydrides relevant to the [NiFe]-hydrogenase active site.

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Nickel-iron dithiolato hydrides relevant to the [NiFe]-hydrogenase active site.

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