Recent progress in the application of group 1, 2 & 13 metal complexes as catalysts for the ring opening polymerization of cyclic esters

Abstract

This review focuses on recent developments concerned with the use of well-defined main group complexes as (pre-)catalysts for the ROP of cyclic esters to give aliphatic polyesters; factors influencing catalytic activity, selectivity and polymer properties are all discussed.

Advances in heterometallic ring-opening (co)polymerisation catalysis

“…Sterically-hindered mono-alkoxide Li/Al complexes 6a-b (Fig. 2 ) were inactive, however the bis-alkoxide 6c-d analogues polymerised LA at room temperature 36 , which is uncommon for Al-based catalysts 23 , 26 . 6c-d were still relatively slow, converting 189 equiv.…”

Combining alkali metals and zinc to harness heterometallic cooperativity in cyclic ester ring-opening polymerisation

“…Al(O i Pr) 3 , however bimetallic catalysts have recently gathered increased attention, 6 with most examples based on biocompatible Al, Ca, Fe, K, Na, Ti and Zn metals. 7 Despite the high activity of alkali metal catalysts, 8 bimetallic zinc catalysts are generally more efficient at combining high activities with polymerisation control in ROP. [9][10][11] We recently reported a highly active bimetallic zincbenzoxide catalyst ([LZn 2 OBn]), 12 based on the Trost ProPhenol ligand (LH 3 ), for the controlled homo-and co-polymerisation of rac-lactide (rac-LA), 3-caprolactone (3-CL) and rac-b-butyrolactone.…”

Structural analysis of five-coordinate aluminium(salen) complexes and its relationship to their catalytic activity

“…There is also a marked lengthening in the aluminium to bridging oxygen distances. In complex 1 these are 1.6827 (6) and 1.6842 (6), whereas for complex 1.HCl the distances are 1.8112 (17) to the fivecoordinate aluminium and 1.9407 (18) to the six-coordinate aluminium.…”

“…Aluminium(salen) complexes in general have been widely used to initiate ringopening polymerisation of cyclic esters. 18 In contrast to six-coordinate metal(salen) complexes, the structures and structural dynamics of five-coordinate metal(salen) complexes have not previously been analysed in detail. This is crucial information needed to facilitate the design of highly active catalysts based on five-coordinate complexes.…”