KINETIC-STUDY OF INTERCONVERSION BETWEEN 2 GEOMETRICAL-ISOMERS OF THE METHOXY-BRIDGED BIS(SILYLENE)IRON COMPLEX, (ETA-C(5)ME(5))(OC)FE((SIME(2))CENTER-DOT-CENTER-DOT-CENTER-DOT-OME-CENTER-DOT-CENTER-DOT-CENTER-DOT(SIMEOME))

Isomerization between two geometrical isomers of the methoxy-bridged bis(silylene)iron complex, anti- and syn-Cp*(OC)Fe{(SiMe(2))... OMe ...(SiMeOMe)} (Cp*=eta(5)-C(5)Me(5)), was investigated by means of a variable-temperature H-1 NMR experiment. The equilibrium constant (K) for the isomerization and its thermodynamic parameters were determined to be K=[syn-isomer]/[anti-isomer]=0.53 at 293 K in toluene-d(8), Delta G degrees(298)=1.5+/-0.5 kJ mol(-1), Delta H degrees=3.8+/-0.2 kJ mol(-1), and Delta S degrees=7.7+/-1.0 J mol(-1) K-1. Computer simulation of the VT spectra and calculation using Eyring equation yielded activation parameters, Delta H-double dagger=83.8+/-3.2 kJ mol(-1), Delta S-double dagger=42.3+/-9.6 J mol(-1) K-1, and Delta G(298)(double dagger)=71.2+/-6.0 kJ mol(-1), for the isomerization from the anti-isomer, in which the terminal OMe group is located on the opposite side of the Cp* group with respect to the Fe-Si-O(bridged)-Si ring, to the syn-isomer. A mechanism in which the bridging OMe group is replaced by the terminal OMe group is proposed for the isomerization.