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Modulation of the electronic structure and the Ni-Fe distance in heterobimetallic models for the active site in [NiFe]hydrogenase.

ABSTRACT: Reaction of the mononuclear Ni(II) thiolate complexes [Ni(L)] [L, L(1), H2L(1), bis(2-mercaptoethyl)-1,2-dimercaptoethane; L(2), H2L(2), N,N'-dimethyl-N,N'-bis(2-mercaptoethyl)-bis(aminoethyl)sulfide] with [FeCp(CO)2I] gives the dithiolate-bridged heterobimetallic species, [Ni(L(1))FeCp(CO)]PF6, 1, and [Ni(L(2))FeCp]I, 2, respectively. Binding of a Fe(CO)3 fragment via reaction of square-planar [Ni(pdt)(dppe)] (dppe, 1,2-diphenylphosphinoethane; pdt(2-), 1,3-propanedithiolate) with Fe3(CO)12 or [Fe(CO)3(BDA)] (BDA, benzylidene acetone) affords diamagnetic [(dppe)Ni(mu-pdt)Fe(CO)3], 3, in which the Ni(II) center is bound tetrahedrally to two thiolate S-donors and to two P-donors. The complex [(dppe)Ni(mu-pdt)Fe(CO)3], 3, reacts in solution via rearrangement to afford [(OC)Ni(mu-dppe)(mu-pdt)Fe(CO)2], 4, in which one P-donor of dppe is bound to Ni and the other to Fe, and a CO ligand has transferred from Fe to Ni. Additionally, the syntheses of 3 and 4 afford the side products [(dppe)Ni(CO)2] and [(OC)3Fe(pdt)Fe(CO)3] together with the trinuclear species [(dppe)(CO)Fe(mu-CO)(mu-pdt)Fe(mu-pdt)Fe(CO)3], 5. Reaction of [Ni(pdt)(dppe)] with [FeCp(CO)2I] in CH2Cl2 affords two products [(dppe)Ni(mu-pdt)FeCp(CO)]PF6, 6, and [(dppe)Ni(pdt)(mu-I)Ni(dppe)]PF6, 7. The complexes 2, 3, and 4 show Ni-Fe distances of 2.539(4), 2.4666(6), and 2.4777(7) A, respectively, with relatively acute dihedral angles of 79.5-81.8 degrees for the Ni-S2-Fe bridge, thus mimicking the shortened Ni...Fe distance (2.5 A) and the acute dihedral angle of the Ni-S2-Fe moiety observed in certain active forms of [NiFe]hydrogenase. The role of direct Ni-Fe bonding in these complexes is discussed and linked to electronic structure calculations on [(dppe)Ni(pdt)Fe(CO)3], 3, which confirm the presence of a bent Ni(d(z2))-Fe(d(z2)) sigma-bond in a singlet ground state.

SUBMITTER: Zhu W

PROVIDER: S-EPMC1317917 | biostudies-literature | 2005 Dec

REPOSITORIES: biostudies-literature

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Modulation of the electronic structure and the Ni-Fe distance in heterobimetallic models for the active site in [NiFe]hydrogenase.

Zhu Wenfeng W Marr Andrew C AC Wang Qiang Q Neese Frank F Spencer Douglas J E DJ Blake Alexander J AJ Cooke Paul A PA Wilson Claire C Schröder Martin M

Proceedings of the National Academy of Sciences of the United States of America 20051213 51

Reaction of the mononuclear Ni(II) thiolate complexes [Ni(L)] [L, L(1), H2L(1), bis(2-mercaptoethyl)-1,2-dimercaptoethane; L(2), H2L(2), N,N'-dimethyl-N,N'-bis(2-mercaptoethyl)-bis(aminoethyl)sulfide] with [FeCp(CO)2I] gives the dithiolate-bridged heterobimetallic species, [Ni(L(1))FeCp(CO)]PF6, 1, and [Ni(L(2))FeCp]I, 2, respectively. Binding of a Fe(CO)3 fragment via reaction of square-planar [Ni(pdt)(dppe)] (dppe, 1,2-diphenylphosphinoethane; pdt(2-), 1,3-propanedithiolate) with Fe3(CO)12 or ...[more]

PMID: 16352727

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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.

Project description:The complex cation in the title compound, (carbonyl-1κC)(1η5-penta-methyl-cyclo-penta-dien-yl)(μ-2,3,9,10-tetra-methyl-1,4,8,11-tetra-thia-undeca-2,9-diene-1,11-diido-1κ2S,S''':2κ4S,S',S'',S''')ironnickel(Fe-Ni) hexa-fluoro-phosphate, [FeNi(C10H15)(C11H18S4)(CO)]PF6 or [Ni(L')FeCp*(CO)]PF6, is composed of the nickel complex fragment [Ni(L')] coordinated as a metalloligand (using S1 and S4) to the [FeCp*(CO)]+ fragment, where (L')2- is [S-C(Me)=C(Me)-S-(CH2)3-S-C(Me)=C(Me)-S]2- and where Cp*- is cyclo-C5(Me)5- (penta-methyl-cyclo-penta-dien-yl). The ratio of hexa-fluoro-phosphate anion per complex cation is 1:1. The structure at 150 K has ortho-rhom-bic (Pbcn) symmetry. The atoms of the complex cation are located on general positions (multiplicity = 8), whereas there are two independent hexa-fluoro-phosphate anions, each located on a twofold axis (Wyckoff position 4c; multiplicity = 4). The structure of the new dimetallic cation [Ni(L')FeCp*(CO)]+ can be described as containing a three-legged piano-stool environment for iron [Cp*Fe(CO)'S2'] and an approximately square-planar 'S4' environment for Ni. The NiS2Fe diamond-shaped substructure is notably folded at the S-S hinge: the angle between the NiS2 plane and the FeS2 plane normals is 64.85 (6)°. Largely because of this fold, the nickel-iron distance is relatively short, at 2.9195 (8) Å. The structural data for the complex cation, which contains a new unsaturated 'S4' ligand (two C=C double bonds), provide an inter-esting comparison with the known NiFe hydrogenase models containing a saturated 'S4'-ligand analogue having the same number of carbon atoms in the ligand backbone, namely with the structures of [Ni(L)FeCp(CO)]+ (as the PF6- salt, CH2Cl2 solvate) and [Ni(L)FeCp*(CO)]+ (as the PF6- salt), where (L)2- is [S-CH2-CH2-S-(CH2)3-S-CH2-CH2-S]2- and Cp- is cyclo-penta-dienyl. The saturated analogues [Ni(L)FeCp(CO)]+ and [Ni(L)FeCp*(CO)]+ have similar Ni-Fe distances: 3.1727 (6), 3.1529 (7) Å (two independent mol-ecules in the unit cell) and 3.111 (5) Å, respectively, for the two complexes, whereas [Ni(L')FeCp*(CO)]+ described here stands out with a much shorter Ni-Fe distance [2.9196 (8) Å]. Also, [Ni(L)FeCp(CO)]+ and [Ni(L)FeCp*(CO)]+ show inter-planar fold angles that are similar between the two: 39.56 (5), 41.99 (5) (independent mol-ecules in the unit cell) and 47.22 (9) °, respectively, whereas [Ni(L')FeCp*(CO)]+ possesses a much more pronounced fold [64.85 (6)°]. Given that larger fold angles and shorter Ni-Fe distances are considered to be structurally closer to the enzyme, unsaturation in an 'S4'-ligand of the type (S-C2-S-C3-S-C2-S)2- seems to increase structural resemblance to the enzyme for structural models of the type [Ni('S4')FeCp R (CO)]+ (Cp R = Cp or Cp*).

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Modulation of the electronic structure and the Ni-Fe distance in heterobimetallic models for the active site in [NiFe]hydrogenase.

Publications

Modulation of the electronic structure and the Ni-Fe distance in heterobimetallic models for the active site in [NiFe]hydrogenase.

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