Heavy ferrocene: a sandwich complex containing Si and Ge atoms.

The heavy analogue of ferrocene (η5-Me5C5)Fe[η5-(CPh)(CH)Si2Ge(SiMetBu2)3] 2, incorporating three heavy group 14 elements in one of the cyclopentadienyl rings, was synthesized by the reaction of the heavy lithium cyclopentadienide [η5-(CPh)(CH)Si2Ge(SiMetBu2)3]·[Li+(thf)] 1-·[Li+(thf)] with (η5-Me5C5)Fe(acac) in THF. The crystal structure analysis of 2 revealed a remarkable flattening of the C2Si2Ge five-membered ring, taking place upon complexation, in which the lengths of all skeletal bonds were intermediate between those of the typical single and double bonds. The one-electron oxidation of 2 occurred at more negative potentials than that of the parent (η5-Me5C5)2Fe:  −0.53 versus −0.32 V. The fragment MO and energy decomposition analyses revealed that the bonding in 2 is predominantly electrostatic, whereas the most important covalent bonding contribution comes from the heavy Cp- ligand to CpFe+ fragment π-donation.