13282-39-8Relevant articles and documents
Lactide polymerization with chiral β-diketiminate zinc complexes
Drouin, Frederic,Oguadinma, Paul O.,Whitehorne, Todd J. J.,Prudhomme, Robert E.,Schaper, Frank
, p. 2139 - 2147 (2010/07/03)
N,N--Di(S-phenylethyl)-2-amino-4-iminopent-2-ene, S,S-nacnac CH(Me)PhH, 1a, and N,N--dibenzyl-2-amino-4-iminopent-2-ene, nacnacBnH, 1b, react with ZnEt2 to form the corresponding nacnacZnEt complexes 2a and 2b. Neither complex is reactive with 2-propanol or methyl lactate to produce the corresponding alkoxide complexes. In reactions with 2b, ligand redistribution occurs and nacnacBn2Zn was obtained. Reaction of 1a and 1b with Zn(N(SiMe3)2) 2 yielded nacnacZnN(SiMe3)2, 6a and 6b. From further reactions with 2-propanol nacnacZnOiPr, 7a and 7b, were obtained. Both complexes were catalytically active for polymerization of rac-lactide with apparent first-order rate constants of kapp = 0.013-0.019 min -1 and 0.019-0.038 min-1 for 7a and 7b, respectively. Obtained polymers were highly heterotactic, with Pr = 0.84-0.87 (7a) and 0.65-0.71 (7b). Analysis of remaining monomer after 75% conversion showed negligible ee and indicates that chiral 7a does not show enantioselectivity in rac-lactide polymerization. Complex 7a, but not 7b, catalyzes unselective transesterification of the polymer during and after polymerization. PLA microstructures in polymerizations with 7b were independent of temperature (23 or 0 °C) or monomer/catalyst ratio (100:1 to 400:1). However, slightly higher Pr values were obtained in the presence of 10-100 equiv of MeCN or pyridine. Complexes nacnacBn2Zn, 2b, 6b, and 7a were characterized by an X-ray diffraction study.
