Modelling nucleophilic substitution at silicon using hypervalent silicon compounds based on urea ligands

The X-ray crystal structure of a pentacoordinate silicon compound, 3, with a urea ligand shows partial Si–O bond formation and Si–Cl cleavage. The solution NMR parameters for the related series of compounds with different leaving groups provides structural information and this can be used to model substitution at silicon. The corresponding thioureas exhibit N–Si bond formation with the silicon remaining tetracoordinate.