Well‐controlled ring‐opening polymerization of cyclic esters catalyzed by aluminum amido complexes: Kinetics and mechanism

Abstract

A series of aluminum dimethyl complexes 1–6 bearing N‐[2‐(pyrrolidinyl)benzyl]anilido ligands were synthesized and well characterized. The molecular structure of complex 1 determined by an X‐ray diffraction study indicates the bidentate chelating mode of the pyrrolidinyl‐anilido ligand. In the absence of a coinitiator, these complexes exhibited excellent control toward the polymerizations of ε‐caprolactone and rac‐lactide, affording polyesters with quite narrow molecular weight distributions (Mw/Mn = 1.04–1.26). The end group analysis of ε−CL oligomer via 1H NMR and ESI‐TOF MS methods gave strong support to the hypothesis that the polymerization catalyzed by these aluminum complexes proceeds via a coordination‐insertion mechanism involving a unique AlN (amido) bond initiation. Via 1H NMR scale oligomerization studies, it is suggested that the insertion of the first lactide monomer into AlN bond of the complex is much easier than the insertion of lactide monomer into the newly formed AlO (lactate) bond and might also be easier than the insertion of the first ε−CL monomer into AlN bond. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 3096–3106

Aluminum alkyl complexes: synthesis, structure, and application in ROP of cyclic esters

“…22) supported by amino-amido ligands, diamido ligands or amidinate ligands were synthesized. [94][95][96][97][98] Without any co-initiator, the aluminum dimethyl complexes 85-87 could polymerize rac-LA or ε-CL in a well-controlled manner, producing polyesters with narrow molecular weight distributions. The results suggested that the ligands in these aluminum dimethyl complexes could act as initiating groups for the ROP of rac-LA or ε-CL in a living manner.…”

Cyclic Carbonates from CO2 and Epoxides Catalyzed by Tetra- and Pentacoordinate Amidinate Aluminum Complexes

“…Amidinic catalysts have recently been used for several reactions, such as olefin polymerization − (Figure , I), ring-opening polymerization of cyclic esters − (Figure , II), and benzamidinate complexes have been applied in the transformation of CO 2 into cyclic carbonates (Figure , III). One of the most interesting properties of the amidinic systems is their capacity to coordinate to different metallic centers, which has allowed incorporation of different elements from the traditional transition metals and expanded the study to elements of greater abundance such as zinc − (Figure , IV), magnesium − (Figure , V), and aluminum − (Figure , VI).…”