Chemo-, Regio-, Stereo- and Chrono-Selectivity Control inPolymerization and Organic Processes by Catalytic Coordination Aggregates: A ”Topochemistry“ in Solution?

Soluble coordination aggregates are usually multinuclear-multiligand entities (M x L y X z ) n hold together by μ-type of bonds, often said electron-deficient. A number of results scattered in the last three decades literature indicate that the size and shape of these aggregates, when used as catalysts, are factors controlling reactions selectivity with unexpected efficiency. This review aims at collecting and discussing a number of such examples in polymer-organic chemistry, including anionic polymerization of (meth)acrylates, ring-opening polymerization of lactones and oxiranes, coordination polymerization of diolefins and lithiation of alkyl aromatics. Under careful control of kinetic and thermodynamic conditions, those processes may exhibit remarkable chemo-, regio-, stereo- and even chrono-selectivity, provided a fine tailoring of the catalytic aggregate structural characteristics. Moreover, some of the examples strongly suggest the occurrence of a ”topochemical“ control in solution, a behaviour usually typical of solid surfaces. Due to the huge potential variety of such aggregates, extension of these ideas as a general and unifying concept is certainly possible, particularly if more sophisticated physical methods are used for the precise characterization of those entities 3D structure.