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 sol ution NMR parameters for the related series of compounds with different lea ving groups provides structural information and this can be used to model s ubstitution at silicon. The corresponding thioureas exhibit N-Si bond forma tion with the silicon remaining tetracoordinate. (C) 2001 Elsevier Science B.V. All rights reserved.