SILASESQUIOXANES AS LIGANDS IN INORGANIC AND ORGANOMETALLIC CHEMISTRY

Silasesquioxanes are an interesting class of ligands for both main gro up and transition-metal elements. A variety of coordination environmen ts can be supported by silasesquioxane ligands, and it is now possible to prepare metallasilsesquioxanes containing practically any stable e lement from Groups 1015. This article surveys the synthesis, character ization, and reactivity of silasesquioxane ligands. Structure, bonding and structural dynamics of both silasesquioxanes and metallasilasesqu ioxanes are also discussed. The chemistry of silasesquioxanes and meta llasilasesquioxanes can provide important insights into the chemistry of silica and silica-supported transition-metal catalysts. The uniquen ess of silasesquioxanes as models for silica is discussed and several systems which provide molecular-level insights into the surface chemis try of silica and silica-supported catalysts are discussed.