Anilido-aldimine aluminum complexes: Synthesis, characterization and lactide polymerization

Abstract

a b s t r a c tThe synthesis of six bimetallic dimethyl aluminum anilido-aldimine complexes, active for the ring opening polymerization of rac-lactide, is reported. An efficient synthetic route to these ligands utilizing isolated lithium amide salts allows for the synthesis of novel cyclohexylamide-substituted ligands, as well as improving the yields of diisopropylphenylamino-substituted ligands, with both ethyl and propyl backbones. Less sterically encumbered methylamide-substituted ligands were prepared through the condensation of ortho-methylaminobenzaldehyde with the appropriate diamine. A monometallic intermediate species, L(AlMe 2 ), was isolated and crystallographically characterized, illustrating the preference these ligands display for bis(bidentate) coordination. L(AlMe 2 ) 2 complexes 8e13 are efficient mediators of the ring opening polymerization of rac-lactide, with solution polymerizations displaying first-order rate constants, molecular weights very close to the theoretical values and polydispersity indexes as low as 1.07.

Retracted Article: Ring-Opening Polymerization of Lactide by Aluminium Catalyst

“…For instance, for determining isotacticity of PLAs, the P m values are calculated from (area of mmm tetrad)(total area in the methine proton region) obtained from Based on the good control over the polymerization reaction, high lewis acidity and low toxicity, aluminium complexes have received a special attention among all the metal-based initiators but their activity is low. [64][65][66][67] Over the past two decades, particular attention has been given to aluminium complexes supported by different ligands, such as Salen [68][69][70][71][72][73] , Salan 80 Nowadays, salen framework type, anilido-aldimine ligand has been used for the synthesis of dimethylaluminium complexes, 81 and these complexes were used for the controlled ROP of rac-LA. The dimethylaluminium complexes stabilized by salicylaldiminate ligands enhance the living as well as controlled polymerization of LA with various polymer microstructures, depending upon the imino substituents of the ligand framework.…”

Monomethylaluminum and dimethylaluminum pyrrolylaldiminates for the ring-opening polymerization of rac-lactide: effects of ligand structure and coordination geometry

“…These observations revealed that both electronic and steric effects in the imino substituent had a strong impact on the catalytic activity. For this study, the activity decreased in the order 4-Me-C 6 H 4 (3) > C 6 H 5 (1) ≈ 4-F-C 6 H 4 (2) ≈ 2-Me-C 6 H 4 (5) > 4-OMe-C 6 H 4 (4) ≫ 2-t Bu-C 6 H 4 (6) > adamantyl (7).…”

“…For complexes 1a-5a and 1b-5b, the polymerizations proceeded to conversion over 84% within 8 hours (in the range of 84-92%) while the polymerizations using complexes 6a and 6b reached 58% and 65% conversion, respectively, at the same period of time. Changing the substituted phenyl group with the adamantyl moiety (7) resulted in a significant decrease of the catalytic activity. The polymerization time of 108 hours was required for complexes 7a and 7b to achieve 91% and 95% conversion, respectively.…”

“…Recently, the anilido-aldimine ligand, closely related to the Salen framework, has been used for the synthesis of dimethylaluminum complexes. 7 These complexes were found to be effective initiators for the controlled ROP of rac-LA. For the bidentate aluminum complexes, most studies have focused on the use of these complexes for the ROP of ε-caprolactone.…”

Zinc Complexes Containing Coumarin-Derived Anilido-Aldimine Ligands as Catalysts for Ring Opening Polymerization of L-Lactide

“…The promising activities and controlled behavior demonstrated by those complexes have encouraged diverse research groups to synthesize similar chelating ligand precursors and examine the bonding and electronic features related to these ligands. Recently some metal complexes containing anilido-aldimine ligands have been reported and demonstrated catalytic activities in ring opening polymerization of cyclic esters [ 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 ]. New ligand precursors working with similar chelating systems should be the attractive candidates.…”