Heterobimetallic Complexes Containing Ca-Fe or Yb-Fe Bonds: Synthesis and Molecular and Electronic Structures of [M{CpFe(CO)2}2(THF)3]2 (M = Ca or Yb)

Reaction of calcium or ytterbium amalgam with [CpFe(CO)2]2 (Fp(2)) gave the isostructural heavy alkaline earth or divalent rare earth compounds [MFp2(THF)(3)](2) (M = Ca or Yb) containing two direct Ca-Fe (3.0185(6) angstrom) or Yb-Fe (2.9892(4) angstrom) bonds. Density functional theory supports experiment in finding shorter Yb-Fe than Ca-Fe distances, and Ziegler-Rauk, molecular orbital, and atoms-in-molecules analyses find the M-Fe bonding to be predominantly electrostatic in nature. The Yb-Fe interaction energy and bond critical point electron density are slightly larger than for Ca-Fe, in agreement with the shorter M-Fe bond in the former. The corresponding reaction for magnesium gave MgFp(2)(THF)(4) with two O-bound Fp moieties and no Mg-Fe bond.