Rare-Earth Complexes Supported by Tripodal Tetradentate Bis(phenolate) Ligands: A Privileged Class of Catalysts for Ring-Opening Polymerization of Cyclic Esters

Abstract

Tripodal dianionic diamino- or amino-alkoxy-bis(phenolate) ligands {ONXOR1,R2} (X = NR2, OR) constitute a privileged class of ligands which has found much interest in combination with group 3 and group 4 metals for generating highly efficient polymerization catalysts. This account article describes the structural variety of and synthetic routes toward trivalent rare-earth complexes incorporating such {ONXOR1,R2} ancillaries along with reactive amido, alkyl, alkoxide, amidinate, guanidinate, halide, and borohydride groups. The chemistry of related divalent rare-earth complexes is also included. This class of Ln{ONXOR1,R2}(R) complexes features outstanding performance in the ring-opening polymerization (ROP) of cyclic esters. Examples of their high reactivity, which has allowed enlarging the scope of ROP reactions to monomers that are difficult to ring-open, and of their ability to control reactions are provided. A particular emphasis is given on their propensity to fine-tune the stereoselectivity of ROP re...