SILICON SILICON INTERACTION IN BIS(SILYLENE)IRON, DISILANYLIRON, AND BIS(SILYL)IRON COMPLEXES

Si-29 NMR coupling constants in a disilanyliron complex CpFe(CO)2SiMe2SiMe(OtBu)2 (1: cp = eta-5-C5H5), a bis(silylene)iron complex Cp(OC)Fe{SiMe2...O((t)Bu)...SiMeOtBu} (2), and a cis-bis(silyl)iron complex (OC)4Fe{SiMe2CH2CH2SiMePh} (3) were measured by the INEPT-INADEQUATE technique. The coupling constant for 2 (28.6 Hz) is much smaller than that for 1 (128 Hz) with a direct Si-Si bond, but larger than that for 3 (2.7 Hz) where there is no direct Si-Si bond. Model calculations using the extended Huckel method indicate that there is no direct bond between the two silicon atoms in the bis(silylene)iron complex Cp(OC)Fe{SiH2...O(H)...SiH2}. This means that the coupling in 2 can be described as the sum of the two geminal couplings, 2J(SiFeSi) and 2J(SiOSi).