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

The 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(AlMe2), was isolated and crystallographically characterized, illustrating the preference these ligands display for bis(bidentate) coordination. L(AlMe2)(2) complexes 8-13 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. (C) 2012 Elsevier B. V. All rights reserved.