REACTIONS OF STERICALLY CONGESTED SECONDARY SILANES WITH IRON CARBONYLS - FORMATION OF MU-SILYLENE COMPLEXES FE2(CO)8(MU-SIR2) (R = MESITYLAND O(2,6-(I)PR2C6H3))

Reaction of dimesitylsilane with enneacarbonyldiiron in hot hexane yie lded octacarbonyl(mu-dimesitylsilylene)diiron as thermally stable yell ow crystals, for which the average bond lengths determined by X-ray cr ystallography are Fe-Fe 2.721(2) and Fe-Si 2.404(2) angstrom, and the Si-29 NMR chemical shift of the bridging silylene is 145.1 ppm. Simila rly, the reaction of bis(2,6-diisopropylphenoxy)silane with dodecacarb onyltriiron in refluxing toluene afforded yl{mu-bis(2,6-diisopropylphe noxy)silylene)di-iron, whereas a similar treatment of the slightly bul kier bis(2,6-di-tert-butylphenoxy)silane with enneacarbonyldiiron or d odecacarbonyltriiron did not give the corresponding mu-silylene comple x.