Lithium, sodium, potassium and calcium amine-bis(phenolate) complexes in the ring-opening polymerization of rac-lactide.

Compounds of Li, Na, K and Ca of a tetradentate amino-bis(phenolato) ligand were prepared. Bimetallic compounds formulated as M-2[L](THF)(n) (where M = Na, n = 1 (1 center dot THF) or Li, n = 1 (2 center dot THF)) were synthesized via the reaction of H-2[L] (where [L] = 2-pyridylmethylamino-N,N-bis(2-methylene-4-methoxy-6-tert-butylphenolato) with sodium hydride or n-butyllithium, respectively, in THF. Monometallic complexes MH[L](THF)(n) (where M = Na, n = 1 (3 center dot THF), Li, n = 0 (4) and K, n = 0 (5)) were obtained by reaction of H-2[L] with MN(SiMe3)(2) where M = Na, Li, or K. Calcium complex Ca[L](THF) (6 center dot THF) was synthesized in two ways; reaction of Na-2[L] with calcium iodide in THF, and reaction of Ca[N(SiMe3)(2)](2) with H-2[L] in toluene. Compounds 1-6 exhibit activity for rac-lactide polymerization under melt and solution conditions. Moderate control of polymer molecular weights was achieved in toluene, whereas polydisperse polymer was obtained under solvent free conditions. MALDI-TOF MS analysis of the polymer end groups revealed a predominantly cyclic nature for the polylactides.