Silicon-silicon interaction in bis(silylene)iron, disilanyliron, and bis(silyl)iron complexes

Abstract

29Si NMR coupling constants in a disilanyliron complex CpFe(CO) 2SiMe 2SiMe(O tBu) 2 ( 1: CP = η 5C 5H 5), a bis(silylene)iron complex Cp(OC)Fe{SiMe 2 ⋯ O( tBu) ⋯ SiMeO tBu)} ( 2), and a cis-bis(silyl)iron complex (OC) 4Fe{SiMe 2CH 2CH 2SiMePh} ( 3) were measured by the INEPT-INADE-QUATE 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 Hückel method indicate that there is no direct bond between the two silicon atoms in the bis(silylene)iron complex Cp(OC)Fe{SiH 2 ⋯ O(H) ⋯ SiH 2}. This means that the coupling in 2 can be described as the sum of the two geminal couplings, 2 J(SiFeSi) and 2 J(SiOSi).