Gallium and indium complexes for ring-opening polymerization of cyclic ethers, esters and carbonates

Over the past five years, Ga(III) and most notably In(III) precursors have attracted a growing interest for application in ROP catalysis of cyclic esters, primarily lactide, and may now be considered as potentially efficient ROP initiators of cyclic esters/carbonates. Despite their higher cost (vs. Al), Ga and In derivatives exhibit key attractive features including: (i) Ga(III) and In(III) are biocompatible metal centers and (ii) their precursors are typically more stable than organoaluminum species in polar media. The present contribution reviews discrete Ga(III) and In(III) compounds thus far developed as ROP initiators of cyclic esters/carbonates. The very few reports on Ga(III)-mediated ROPs of cyclic ethers are also included. In addition to the ROP performances of such species, the synthesis and structural characterization of these initiators are also provided and thoroughly discussed with, whenever appropriate, the establishment of structure/reactivity relationships and mechanistic pathways.

► Coordination chemistry of Ga(III) and In(III) to prepare well-defined charge-neutral, cationic and anionic complexes.
► Synthetic methodologies and structural features of such compounds.
► Use of those discrete complexes as initiators/catalysts in ring-opening polymerization of cyclic esters and ethers.
► Catalytic performances, structure/reactivity relationships and operative ROP mechanisms described and contrasted with those of their Al(III) analogs.