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Precursors to [FeFe]-Hydrogenase Models: Syntheses of Fe2(SR)2(CO)6 from CO-Free Iron Sources

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posted on 2008-08-04, 00:00 authored by Phillip I. Volkers, Christine A. Boyke, Jinzhu Chen, Thomas B. Rauchfuss, C. Matthew Whaley, Scott R. Wilson, Haijun Yao
This report describes routes to iron dithiolato carbonyls that do not require preformed iron carbonyls. The reaction of FeCl2, Zn, and Q2S2CnH2n (Q+ = Na+, Et3NH+) under an atmosphere of CO affords Fe2(S2CnH2n)(CO)6 (n = 2, 3) in yields >70%. The method was employed to prepare Fe2(S2C2H4)(13CO)6. Treatment of these carbonylated mixtures with tertiary phosphines, instead of Zn, gave the ferrous species Fe3(S2C3H6)3(CO)4(PR3)2, for R = Et, Bu, and Ph. Like the related complex Fe3(SPh)6(CO)6, these compounds consist of a linear arrangement of three conjoined face-shared octahedral centers. Omitting the phosphine but with an excess of dithiolate, we obtained the related mixed-valence triiron species [Fe3(S2CnH2n)4(CO)4]. The highly reducing all-ferrous species [Fe3(S2CnH2n)4(CO)4]2− is implicated as an intermediate in this transformation. Reactive forms of iron, prepared by the method of Rieke, also combined with dithiols under a CO atmosphere to give Fe2(S2CnH2n)(CO)6 in modest yields under mild conditions. Studies on the order of addition indicate that ferrous thiolates are formed prior to the onset of carbonylation. Crystallographic characterization demonstrated that the complexes Fe3(S2C3H6)3(CO)4(PEt3)2 and PBnPh3[Fe3(S2C3H6)4(CO)4] feature high-spin ferrous and low-spin ferric as the central metal, respectively.