Organosilicon platforms: Bridging homogeneous, heterogeneous, and bioinspired catalysis

Organosilicon compounds, in the form of cubic metallasiloxanes, cage-like silsesquioxanes, macromolecular nanocages, and flexible structures such as dendrimers and linear metallsiloxanes, have found useful applications as catalysts, ligands for metal complexes, and catalyst supports. Illustrative examples of these are presented. The well-defined structures of these compounds make them particularly suitable as molecular analogues of zeolites or silica-supported catalysts. A unique feature of many of these compounds is the presence of flexible siloxane bonds, which accommodate large fluctuations in the framework geometry, reminiscent of the adaptability of enzymes to conformational changes, and distinguish siloxane containing materials from carbon based synthetic materials. New preparative pathways and the use of the versatile silyl ester as a protection group have greatly expanded synthetic possibilities, pointing to the possibility of assembling these structures to form multifunctional catalytic structures. Some nanocage structures, with functionalities organized in close proximity, exhibit nanoconfinement effects.