Three aluminium alkoxide complexes containing N(2)O(2) bis(phenoxy)-amine ligands were synthesized from reactions of the corresponding N(2)O(2) ligands with Al(O(i)Pr)(3) in toluene. Different amine side chains of the ligands included pyridine (1), CH(2)NMe(2) (2), and CH(2)NEt(2) (3). The related chloro aluminium analog (4) was prepared from a reaction between AlCl(3) and the potassium salt of the N(2)O(2) ligand having CH(2)NMe(2) side chain. X-Ray crystallography reveals that complexes 3 and 4 have a monomeric five-coordinate aluminium center. Complexes 1-3 catalyzed the polymerization of epsilon-caprolactone (epsilon-CL) at 70 degrees C in toluene with the relative reactivities of 1<2< 3. In contrary, only complex 1 was active for the polymerization of lactide under the same polymerization conditions. (1)H NMR spectroscopy shows that treatment of 2 with 1 equivalent of lactide afforded the ring-opened product L(2)Al-OCH(Me)C(O)OCH(Me)C(O)O(i)Pr. Electronic effects are believed to be responsible for the observed trend in the epsilon-CL polymerization rates. On the other hand, steric hindrance at the amine side chain is the main contributor to the observed rates of lactide polymerization.

The bowl‐shaped aluminum alkoxide complexes bearing N2O2 bis(phenolate)‐amine ligands having different side arms as pyridine (1), dimethyl amine (2), and diethyl amine (3) were shown to be highly efficient and well behaved in the homopolymerization and copolymerization of l‐lactide (LA) and ε‐caprolactone (ε‐CL) at 100 °C. The rates of copolymerization are similar for Complexes 1–3 where nearly full conversions were achieved in 60 h for [LA]:[CL]:[Al] ratio of 50:50:1. The minor adjustment of the side arms of the Catalysts 1–3 gave profound differences in the LA/ε‐CL copolymer sequences where tapered, gradient, and highly random structures were obtained in one system, respectively. The chelation of LA to Al metal after ring‐opening process and suitable steric hindrance of the side arms were believed to participate and saturate the aluminum metal centers giving different copolymer structures. The random LA/ε‐CL copolymer structure was confirmed by nuclear magnetic resonance and differential scanning calorimetry analysis. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1635–1644

Polymerizations of biodegradable lactide and lactones have been the subjects of intense research during the past decade. They can be polymerized/copolymerized effectively by several catalyst systems. With bis(phenolate)-amine aluminum complex, we have shown for the first time that lactide monomer can deactivate the aluminum complex during the ongoing polymerization of ε-caprolactone to a complete stop. After hours of dormant state, the aluminum complex can be reactivated again by heating at 100 °C without the addition of any external chemicals still giving polymer with narrow dispersity. Studies using NMR, in situ FTIR, and single-crystal X-ray crystallography indicated that the coordination of the carbonyl group in lactyl unit was responsible for the unusual behavior of lactide. In addition, the unusual methyl-migration from methyl lactate ligand to the amine side chain of the aluminum complex was observed through intermolecular nucleophilic-attack mechanism.

The effects of appended hydroxyl groups and the chain length of a series of (imino)pyridine ligands on copper coordination and copper-catalyzed aerobic oxidation of alcohols were investigated.

A series of imine and amine Schiff-base tin(ii) complexes were synthesized. Complexes having dimethylamino side arm appears to be innocent while those having pyridyl side arm underwent unusual ligand dimerization.

New homoleptic zinc and magnesium complexes containing constrained reduced Schiff base ligands based on substituted 7-hydroxy-1-indanone were successfully synthesized and used as a catalyst for the polymerization of lactide. The ligands contain a side arm having different basicity because dimethylamino, pyridyl, and furfuryl groups are shown to greatly affect the polymerization rates. The homoleptic zinc complex containing constrained reduced Schiff base ligands and a dimethylamino side arm was highly active, giving a 92% conversion of l-lactide in 3 min using [LA]:[Zn]:[BnOH] = 500:1:2 at room temperature. The polymerization is pseudo-first-order dependent on the LA concentration. Well-controlled and living behavior of the zinc complex was observed and demonstrated in the preparation of stereodiblock and triblock copolymers of l -, d-, and rac-lactide in a one-pot sequential synthesis with a predictable block length, block sequence, and narrow dispersity rapidly in 10 min. Stereocomplex formation was observed for PLA made sequentially from 100 l-LA, 100 rac-LA, and 100 d-LA having a high T m of up to 220 °C.

Seven constrained aluminum inden complexes having different substituents and diamine backbones were developed for the ring-opening copolymerization (ROCOP) of epoxides and bulky cyclic anhydrides giving alternating polyesters with T g ranging from 49 to 226 °C. Among several catalyst/cocatalyst screenings, the aluminum inden complex having a rigid phenylene backbone coupled with 4-dimethylaminopyridine showed the best performance giving linear polyesters. In the case of cyclohexene oxide (CHO) and succinic anhydride (SA), the linear poly(CHO-alt-SA) could be transformed to cyclic polymer when the polymerization was left under prolonged reaction time to induce intramolecular transesterification. The kinetic studies of the ROCOP revealed a zeroth-order dependence on cyclic anhydride and a first-order dependence on epoxide and the catalyst. The catalysts can be extended efficiently to the one-pot CHO/PA/l-lactide terpolymerization giving uncommon tapered copolymers of poly(CHO-alt-PA) and PLA via switchable polymerization.

Bis(amidinate) tin(II) complex (1) was reported as active catalyst for ring‐opening copolymerization of cyclic anhydrides and epoxides via a binary catalyst system. Polymerizations of six combinations of epoxides and cyclic anhydrides were carried out giving highly alternating poly(anhydride‐alt‐epoxide) with narrow dispersities, except for cyclohexene oxide where significant amount of ether linkage up to 62 % was observed. This ether linkages could be diminished by increasing the amount of cocatalyst to over 3 equiv. Six well‐known cocatalysts were screened where PPNCl was found to be the best cocatalyst.