Use of Metal Catalysts Bearing Schiff Base Macrocycles for the Ring Opening Polymerization (ROP) of Cyclic Esters

Abstract

Schiff base macrocycles are emerging as useful scaffolds for binding two or more catalytic metals in close proximity. Such coordination chemistry allows for the evaluation of potentially beneficial catalytic cooperative effects. In the field of ring opening polymerization (ROP) of cyclic esters, only a handful of metal systems bound by Schiff base [2 + 2] type macrocycles have been studied. Nevertheless, results to date have, for certain metals, identified some interesting structure activity relationships, whilst for other systems results have revealed particular combinations of metals and macrocycles to be virtually inactive. This perspective review takes a look at two types of recently-reported Schiff base macrocycles that have been employed as pro-ligands in the metal-catalyzed ROP of cyclic esters, specifically ε-caprolactone and rac-lactide.

Factors influencing catalytic behavior of titanium complexes bearing bisphenolate ligands toward ring-opening polymerization of L-lactide and ε-caprolactone

“…These polymers have vast applications in many fields [3,4]. Metal catalysts [5][6][7] have been commonly used as catalysts for the ROP of cyclic esters. Since PLA and PCL polymers have wide application in medical field, the minimization of residual hazardous metal in these polymers after synthesis is essential.…”

Use of pyrazoles as ligands greatly enhances the catalytic activity of titanium iso-propoxide for the ring-opening polymerization of l-lactide: a cooperation effect

“…One of the methods of PLA synthesis is the Lewis acidic metal-catalyzed ring-opening polymerization (ROP) of cyclic esters. [22][23][24][25][26][27][28][29][30][31] For biomaterials, metal residuals present in resulting PLA are a serious problem, and using catalysts with non-cytotoxic metals is a straightforward approach to solving this problem. Because of the non-cytotoxic property and strong Lewis acidity of titanium, Ti complexes 22,23,[30][31][32][33] are commonly used catalysts in LA ROP.…”

Polynuclear alkoxy–zinc complexes of bowl-shaped macrocycles and their use in the copolymerisation of cyclohexene oxide and CO2

“…Multidentate macrocycles are attractive as ligands for di-and polynuclear complexes of transition-and f-block metals as they can control both the basic coordination chemistry and the relative spatial positioning of metals within the macrocyclic framework, so providing a pre-organised chemical environment. [1][2][3][4] This ligand design strategy can deliver a diversity of physical and reaction properties in the resulting complexes leading to, for example, clustering and aggregation, [5][6][7][8][9][10][11][12][13][14] catalytic activity, [15][16][17][18][19][20][21][22][23][24][25][26][27][28] molecular magnetism, 29 allosteric constructs, 30,31 and molecular sensing. [32][33][34][35] We have been studying macrocycles in which two donor compartments comprising two dipyrromethane and two Schiff-base nitrogen donors (i.e.…”