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

Abstract The synthesis of the new complexes Cp*(dppe)Fe C C 2,5-C 4 H 2 SR (Cp* = 1,2,3,4,5-pentamethylcyclopentadienyl; dppe = 1,2-bis(diphenylphosphino)ethane; 2a , R = C CH; 2b , R = C C Si(CH 3 ) 3 ; 2c , R = C C Si(CH(CH 3 ) 2 ) 3 ; 3a , R = C C 2,5-C 4 H 2 S C CH; 3c , R = C C 2,5-C 4 H 2 S C C Si(CH(CH 3 ) 2 ) 3 ) is described. The 13 C 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 [Cp 2 Fe][PF 6 ]. The corresponding complexes 2a [PF 6 ] and 3c [PF 6 ] are thermally stable, but 2a [PF 6 ] 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.