The reaction of Fe<sub>2</sub>(S<sub>2</sub>C<sub>2</sub>H <sub>4</sub>)(CO)<sub>6</sub> with cis-Ph<sub>2</sub>PCH=CHPPh<sub>2</sub> (dppv) yields Fe<sub>2</sub>(S<sub>2</sub>C<sub>2</sub>H<sub>4</sub>)(CO) <sub>4</sub>(dppv), 1(CO)<sub>4</sub>, wherein the dppv ligand is chelated to a single iron center. NMR analysis indicates that in 1(CO)<sub>4</sub>, the dppv ligand spans axial and basal coordination sites. In addition to the axial-basal isomer, the 1,3-propanedithiolate and azadithiolate derivatives exist as dibasal isomers. Density functional theory (DFT) calculations indicate that the axial-basal isomer is destabilized by nonbonding interactions between the dppv and the central NH or CH<sub>2</sub> of the larger dithiolates. The Fe(CO) <sub>3</sub> subunit in 1(CO)<sub>4</sub> undergoes substitution with PMe <sub>3</sub> and cyanide to afford 1(CO)<sub>3</sub>(PMe<sub>3</sub>) and (EttN)[1(CN)(CO)<sub>3</sub>], respectively. Kinetic studies show that 1(CO)<sub>4</sub> reacts faster with donor ligands than does its parent Fe <sub>2</sub>(S<sub>2</sub>C<sub>2</sub>H<sub>4</sub>)(CO)<sub>6</sub>. The rate of reaction of 1(CO)<sub>4</sub> with PMe<sub>3</sub> was first order in each reactant, k = 3.1 × 10<sup>-4</sup> M<sup>-1</sup> s<sup>-1</sup>. The activation parameters for this substitution reaction, ΔH‡ = 5.8(5) kcal/mol and ΔS‡ = -48(2) cal/deg·mol, indicate an associative pathway. DFT calculations suggest that, relative to Fe <sub>2</sub>(S<sub>2</sub>C<sub>2</sub>H<sub>4</sub>)(CO)<sub>6</sub>, the enhanced electrophilicity of 1(CO)<sub>4</sub> arises from the stabilization of a "rotated" transition state, which is favored by the unsymmetrically disposed donor ligands. Oxidation of MeCN solutions of 1(CO) <sub>3</sub>(PMe<sub>3</sub>) with Cp<sub>2</sub>FePF<sub>6</sub> yielded [Fe<sub>2</sub>(S<sub>2</sub>C<sub>2</sub>H<sub>4</sub>)(μ-CO)(CO) <sub>2</sub>(dppv)(PMe<sub>3</sub>)(NCMe)](PF<sub>6</sub>)<sub>2</sub>. Reaction of this compound with PMe<sub>3</sub> yielded [Fe<sub>2</sub>(S <sub>2</sub>C<sub>2</sub>H<sub>4</sub>)-(μ-CO)(CO)(dppv)(PMe <sub>3</sub>)<sub>2</sub>(NCMe)](PF<sub>6</sub>)<sub>2</sub>. © 2007 American Chemical Society.
Justice, A., Zampella, G., DE GIOIA, L., Rauchfuss, T., van der Vlugt, J., Wilson, S. (2007). Chelate control of diiron(I) dithiolates relevant to the [Fe-Fe]-hydrogenase active site. INORGANIC CHEMISTRY, 46(5), 1655-1664 [10.1021/ic0618706].
Chelate control of diiron(I) dithiolates relevant to the [Fe-Fe]-hydrogenase active site
ZAMPELLA, GIUSEPPE;DE GIOIA, LUCA;
2007
Abstract
The reaction of Fe2(S2C2H 4)(CO)6 with cis-Ph2PCH=CHPPh2 (dppv) yields Fe2(S2C2H4)(CO) 4(dppv), 1(CO)4, wherein the dppv ligand is chelated to a single iron center. NMR analysis indicates that in 1(CO)4, the dppv ligand spans axial and basal coordination sites. In addition to the axial-basal isomer, the 1,3-propanedithiolate and azadithiolate derivatives exist as dibasal isomers. Density functional theory (DFT) calculations indicate that the axial-basal isomer is destabilized by nonbonding interactions between the dppv and the central NH or CH2 of the larger dithiolates. The Fe(CO) 3 subunit in 1(CO)4 undergoes substitution with PMe 3 and cyanide to afford 1(CO)3(PMe3) and (EttN)[1(CN)(CO)3], respectively. Kinetic studies show that 1(CO)4 reacts faster with donor ligands than does its parent Fe 2(S2C2H4)(CO)6. The rate of reaction of 1(CO)4 with PMe3 was first order in each reactant, k = 3.1 × 10-4 M-1 s-1. The activation parameters for this substitution reaction, ΔH‡ = 5.8(5) kcal/mol and ΔS‡ = -48(2) cal/deg·mol, indicate an associative pathway. DFT calculations suggest that, relative to Fe 2(S2C2H4)(CO)6, the enhanced electrophilicity of 1(CO)4 arises from the stabilization of a "rotated" transition state, which is favored by the unsymmetrically disposed donor ligands. Oxidation of MeCN solutions of 1(CO) 3(PMe3) with Cp2FePF6 yielded [Fe2(S2C2H4)(μ-CO)(CO) 2(dppv)(PMe3)(NCMe)](PF6)2. Reaction of this compound with PMe3 yielded [Fe2(S 2C2H4)-(μ-CO)(CO)(dppv)(PMe 3)2(NCMe)](PF6)2. © 2007 American Chemical Society.
I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
