Heavy ferrocene: A sandwich complex containing Si and Ge atoms

The heavy analogue of ferrocene (η⁵-Me₅C₅)Fe[η⁵-(CPh)(CH)Si₂Ge(SiMe^tBu₂)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.