Substitution and S-alkylation reactions of thiocarbonyl-bridged Cp2Fe2(CO)3CS

Article abstract of DOI:10.1021/ic50218a033

In refluxing CH₃CN, Cp₂Fe₂(CO)₃CS reacts with PEt₃, PMe₂Ph, PMePh₂, and P(OMe)₃ to give the monosubstituted derivatives Cp₂Fe₂(CO)₂(PR₃)CS, in which the CS group remains in the bridging position, as it does in all of the complexes described in this report. The reaction of MeNC with Cp₂Fe₂(CO)₃CS in refluxing THF or cyclohexane gives Cp₂Fe₂-(CO)₂(MeNC)CS which exists predominantly as an isomer in which the MeNC is terminal. There is, however, spectroscopic evidence for a less abundant isomer in which the MeNC is bridging. The bissubstituted complex Cp₂Fe₂(CO)(MeNC)₂CS may be obtained by refluxing Cp₂Fe₂(CO)₃CS and MeNC in acetonitrile. This complex has been partially separated chromatographically into a major isomer, in which one MeNC is bridging and the other is terminal, and a minor bis-terminal MeNC isomer. The bridging thiocarbonyl sulfur atom of CpFe₂(CO)₃CS may be alkylated at room temperature by reaction with alkyl iodides, benzyl bromide, allyl bromide, MeOSO₂F, and Et₃O⁺ to give the Cp₂Fe₂(CO)₃CSR⁺ complexes. The methyl derivative Cp₂Fe₂(CO)₃CSMe⁺ reacts readily with ligands PEt₃, PMe₂Ph, PMePh₂, P(OMe)₃, and MeNC to give the CO-substituted products Cp₂Fe₂(CO)₂(L)CSMe⁺. Both alkylation and substitution occur when Cp₂Fe₂(CO)₃CS is refluxed in acetonitrile with MeI and NaI to give Cp₂Fe₂(CO)₂(I)(CSMe). Only the CS-alkylated product Cp₂Fe₂-(CO)₂(MeNC)CSMe⁺ is obtained from the reaction of Cp₂Fe₂(CO)₂(MeNC)CS with MeOSO₂F or MeI. The bissubstituted complex Cp₂Fe₂(CO)(MeNC)₂CS reacts with MeI to yield the CS-alkylated compound Cp₂Fe₂(CO)(MeNC)₂CSMe⁺ in which both of the MeNC groups are terminal. With the stronger alkylating MeOSO₂F, this complex gives the dimethylated product Cp₂Fe₂(CO)(MeNC)(Me₂NC)CSMe²⁺, in which both alkylated groups are bridging. All of the complexes are characterized by their IR and ¹H and ¹³C NMR spectra, which give evidence of isomers in which the Cp rings are cis or trans to each other across the Fe-Fe bond. Mechanisms for the interconversion of several of the isomers are discussed.