| Abstrakt: |
In the search for complexes modeling the [Fe(CN)2(CO)(cysteinate)2] cores of the active centers of [NiFe] hydrogenases, the complex (NEt4)2[Fe(CN)2(CO)(′S3′)] (4) was found (′S3′2−=bis(2‐mercaptophenyl)sulfide(2−)). Starting complex for the synthesis of 4was [Fe(CO)2(′S3′)]2(1). Complex 1formed from [Fe(CO)3(PhCH=CHCOMe)] and neutral ′S3′−H2. Reactions of 1with PCy3or DPPE (1,2‐bis(diphenylphosphino)ethane) yielded diastereoselectively [Fe(CO)2(PCy3)(′S3′)] (2) and [Fe(CO)(dppe)(′S3′)] (3). The diastereoselective formation of 2and 3is rationalized by the transinfluence of the ′S3′2−thiolate and thioether S atoms which act as π donors and π acceptors, respectively. The transinfluence of the ′S3′2−sulfur donors also rationalizes the diastereoselective formation of the C1symmetrical anion of 4, when 1is treated with four equivalents of NEt4CN. The molecular structures of 1, 3⋅0.5 C7H8, and (AsPh4)2[Fe(CN)2(CO)(′S3′)] ⋅acetone (4 a⋅C3H6O) were determined by X‐ray structure analyses. Complex 4is the first complex that models the unusual 2:1 cyano/carbonyl and dithiolate coordination of the [NiFe] hydrogenase iron site. Complex 4can be reversibly oxidized electrochemically; chemical oxidation of 4by [Fe(Cp)2PF6], however, led to loss of the CO ligand and yielded only products, which could not be characterized. When dissolved in solvents of increasing proton activity (from CH3CN to buffered H2O), complex 4exhibits drastic ν(CO) blue shifts of up to 44 cm−1, and relatively small ν(CN) red shifts of approximately 10 cm−1. The ν(CO) frequency of 4in H2O (1973 cm−1) is higher than that of any hydrogenase state (1952 cm−1). In addition, the ν(CO) frequency shift of 4in various solvents is larger than that of [NiFe] hydrogenase in its most reduced or oxidized state. These results demonstrate that complexes modeling properly the ν(CO) frequencies of [NiFe] hydrogenase probably need a [Ni(thiolate)2] unit. The results also demonstrate that the ν(CO) frequency of [Fe(CN)2(CO)(thiolate)2] complexes is more significantly shifted by changing the solvent than the ν(CO) frequency of [NiFe] hydrogenases by coupled‐proton and electron‐transfer reactions. The “iron‐wheel” complex [Fe6{Fe(′S3′)2}6] (6) resulting as a minor by‐product from the recrystallization of 2in boiling toluene could be characterized by X‐ray structure analysis. |
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