29Si NMR of pentacoordinate silicon derivatives

Abstract 29 Si NMR is useful as a direct probe for intramolecular pentacoordination in the compounds o -(Me 2 NCH 2 )C 6 H 4 SiXYZ. The temperature dependence of chemical shifts indicates the existence of an equilibrium between tetra- and penta-coordinate forms. α-Np[ o -Me 2 NCH 2 )]C 6 H 4 SiH 2 proves to be the first silicon derivative without halogen or chalcogen to show intramolecular pentacoordination. This coordination may account for the reactivity of the SiH bond in this compound.