(NEt_4)_2[Fe(CN)_2(CO)('S_3')]:An Iron Thiolate Complex Modeling the [Fe(CN)_2(CO)(S-Cys)_2]site of [NiFe]hydrogenase centers

摘要

In the search for complexes modeling the [Fe(CN)_2(CO)(cysteinate)_2]cores of the active centersof [NiFe] hydrogenases,the complex(NEt_4)_2[Fe(CN)_2(CO)('S_3')](4)was found ('S_2'~(2-)-bis(2-m)ercaptophenyl-sulfide(2-).Starting complex for the synthesis of 4 was [Fe(CO)_2('S_3')]_2(1).Complex 1 formed from [Fe(CO)_3-(PhCH=CHCOMe)]and neutral 'S_3'-H_2.Reactions of 1 with PCy_3or DPPE (1,2-bis(diphenylphosphion)-ethane)yielded diastereoselectively[Fe(CO)_2(PCy_3)('S_3')](2)and[Fe(CO)-(dppe)('S_3')](3).Thediastereoselective formation of 2 and 3is rationalized by the trans influence of the 'S_3'~(2-) thiolate and thioether S atome which act as #pi# donors and #pi# acceptors,respectively.The trans influence of the 'S_3'~(2-)sulfur donors also rationalizes the diastereoselective formation ofthe C_1 symmetrical anion of 4,when 1 is treated with four equivalents of NEt_4CN.The molecular structures of 1,3.0.5C_7H_8,and (AsPh_4)_2[Fe(CN)_2(CO)('S_3')].acetone(4a.C_3H_6O)were determined by X-raystructure analyses.Complex 4 is the first complex that models the unusual 2:1 cyano/carbonyland dithiolate coordination of the [NiFe] hydrogenase iron site.Complex that models the unusual 2:1 cyano/carbonyl and dithiolate coordination of the [NiFe] hydrogenase iron site.Complex 4 can be reversibly oxidized electrochemically;chemicaloxidation of 4 by [Fe(Cp)_2PF_6].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 CH_3CN to buffered H_2O),complex 4 exhibits drastic v(CO) blue shifts of up to 44 cm~(-1),and relatively small v(CN) red shifts of approximately 10 cm~(-1).The v(CO) frequency of 4 in H_2O (1973cm~(-1))is higher than that of any hydrogenase state(1951cm~(-1)).In addition,the v(CO)frequency shift of 4 in various solvents is larger than that of [NiFe] hydrogenase in its most reduced or oxidized state.These results demonstrate that complexes modeling properly the v(CO)frequencies of [NiFe]hydrogenase probably needa [Ni(thiolate)_2]unit.The results also demonstrate that the v(CO) frequency of [Fe(CN)_2(CO)-(thiolate)_2]complexes is more significantly shifted by changing the solvent that the v(CO) frequency of [NiFe]hydrogenasesby coupled-proton and electron-transferreactions.The "iron-wheel"complex [Fe_6{Fe('S_3')_2}_6](6)resulting as a minor by-product from the recrystallization of 2 in boiling toluene could be characterized by X-ray structure analysis.