How Strained are [1]Ferrocenophanes?

A series of [1]­ferrocenophanes
([1]­FCPs) bridged by boron, carbon,
silicon, phosphorus, and sulfur, respectively, were investigated by
DFT calculations. A comparison of measured molecular structures with
calculated structures showed that the applied B3PW91/6-311+G­(d,p)
level of theory provides realistic molecular geometries. Geometry
optimization of carbon-bridged [1]­FCPs (ERx = CH2, CMe2) revealed that these unknown species
with tilt angles α of 38.5° may be sufficiently stable
to allow isolation, given sufficient kinetic stability. In order to
measure the amount of strain in [1]­FCPs, a hypothetical 1,2-addition
of a C–H group of FeCp2 across the E–Cipso bond of a [1]­FCP to give a bis­(ferrocenyl)­species was
investigated. The calculated reaction enthalpies were compared to
experimental ΔHROP values as obtained
from differential scanning calorimetry (DSC) measurements.