Synthesis, characterization, and electrochemistry of dicyclopentadienylsiloxane-bridged dicarbonyldi-iron

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The new metal–metal bonded binuclear iron complexes [{Fe(CO)2}2{η5:η5′-C5H4(RR′SiO)nSiRR′C5H4}][R = R′= Me, n= 1 (1) or 2 (2); R = Me, R′= Ph, n= 1 (3)] have been prepared in good yield by reaction between dicyclopentadienylsiloxanes, C5H5(RR′SiO)nSiRR′C5H5(R = R′= Me, n= 1 or 2; R = Me, R′= Ph, n= 1), and [Fe(CO)5]. Oxidation of (1)–(3) with [Fe(η5-C5H5)2]PF6 in the presence of PPh3 gives the dicationic complexes [{Fe(CO)2(PPh3)}2{η5:η5′-C5H4(RR′SiO)nSiRR′C5H4}][PF6]2[R = R′= Me, n= 1 (7) or 2 (8); R = Me, R′= Ph,n= 1 (9)]. The dianionic complexes K2[{Fe(CO)2}2{η5:η5′-C5H4(RR′SiO)nSiRR′C5H4}][R = R′= Me, n= 1 (10) or 2 (11); R = Me, R′= Ph, n= 1 (12)] were obtained by treating (1)–(3) with potassium diphenylketyl. The new binuclear iron complexes have been characterized by 1H and 13C n.m.r. and i.r. spectroscopy. The electrochemistry of compounds (1)–(3) indicates that two-electron oxidation products are stable on the voltammetric time-scale. Their kinetic stability depends upon the solvent donicity. The final products are dication complexes which do not contain carbonyl bridges (4)–(6).