Iron(II) and iron(III) complexes containing ethynyl thiophene fragments

The synthesis of the new complexes Cp*(dppe)Fesingle bondCtriple bond; length of mdashCsingle bond2,5-C4H2SR (Cp* = 1,2,3,4,5-pentamethylcyclopentadienyl; dppe = 1,2-bis(diphenylphosphino)ethane; 2a, R = Ctriple bond; length of mdashCH; 2b, R = Ctriple bond; length of mdashCsingle bondSi(CH3)3; 2c, R = Ctriple bond; length of mdashCsingle bondSi(CH(CH3)2)3; 3a, R = Ctriple bond; length of mdashCsingle bond2,5-C4H2Ssingle bondCtriple bond; length of mdashCH; 3c, R = Ctriple bond; length of mdashCsingle bond2,5-C4H2Ssingle bondCtriple bond; length of mdashCsingle bondSi(CH(CH3)2)3) is described. The 13C NMR and FTIR spectroscopic data indicate that the π-back donation from the metal to the carbon rich ligand increases with the size of the organic π-electron systems. The new complexes were also analyzed by CV and the chemical oxidation of 2a and 3c was carried out using 1 equiv of [Cp2Fe][PF6]. The corresponding complexes 2a[PF6] and 3c[PF6] are thermally stable, but 2a[PF6] was too reactive to be isolated as a pure compound. The spectroscopic data revealed that the coordination of large organic π-electron systems to the iron nucleus produces only a weak increase of the carbon character of the SOMO for these new organoiron(III) derivatives.