Thermal treatment of
t-BuC
5H
4Me
2SiSiMe
2C
5H
4-
t-Buwith Fe(CO)
5 in xylene gave thediiron complex(Me
2SiSiMe
2)[(
5-
t-BuC
5H
3)Fe(CO)]
2(
-CO)
2(
3), existing as a mixture of cisand trans isomers (
3c and
3t) which wereseparated by preparative TLC. When the twoisomers were heated respectively in xylene, the cis substrate(
3c) rearranged to the transproduct[Me
2Si(
5-
t-BuC
5H
3)Fe(CO)
2]
2(
4t), while the trans substrate (
3t) afforded thecisproduct[Me
2Si(
5-
t-BuC
5H
3)Fe(CO)
2]
2(
4c). This indicates that the rearrangementreactionis stereospecific. Complexes[(
5:
5-C
5H
4Me
2SiSiMe
2C
5R
3R')Fe(CO)]
2(
-CO)
2(R = H, R' =
t-Bu,
5; R = R' = Me,
6),containing different cyclopentadienyl groups, werepreparedsimilarly. Their respective rearrangement reactions only yieldedthe corresponding unsymmetrical products[(Me
2Si)(
5-C
5H
4)Fe(CO)
2][(Me
2Si)(
5-C
5R
3R')Fe(CO)
2](R = H, R' =
t-Bu,
7; R = R' = Me,
8); no symmetricaldisproportionation products were detected. Thisindicatesthat the reaction proceeds via an intramolecular rather thanintermolecular pathway. Theconclusion is further confirmed by the fact that no crossover productwas formed insubsequent rearrangement between two different substrates. Probingthe reaction by ESRspectroscopy shows that the reaction proceeds via an intermediatecontaining iron-centeredradicals. On the basis of these experimental facts, an alternativemechanism for therearrangement reaction is proposed. Molecular structures of
3c,
3t,
4t, and
4cweredetermined by X-ray diffraction.