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投稿者: Yuma Morimoto

Article

Square-Planar Cu(II) Diketiminate Complexes in Lactide Polymerization

Département de chimie, Université de Montréal, 2900 Boul. E.-Montpetit, Montréal, Quebec, H3T 1J4,Canada
Inorg. Chem., 2013, 52 (23), pp 13612–13622
DOI: 10.1021/ic402133c
Publication Date (Web): November 18, 2013
Copyright © 2013 American Chemical Society

Synopsis

Copper(II) bisdiketiminate complexes catalyze the polymerization of lactide with very good activities in the presence of alcohol or with extremely high activities as the isolated heteroleptic alkoxide complex.
Inorganic Chemicals and Reactions

Abstract

Abstract Image
Cu(OiPr)2 was reacted with several β-diketimine ligands, nacnacRH. Sterically undemanding ligands with N-benzyl substituents afforded the dimeric heteroleptic complexes [nacnacBnCu(μ-OiPr)]2 and [3-Cl-nacnacBnCu(μ-OiPr)]2 (Bn = benzyl). With sterically more demanding amines, dimerization was not possible, and the putative nacnacCuOiPr intermediate underwent ligand exchange to the homoleptic bisdiketiminate complexes Cu(nacnacipp)2 and Cu(nacnacNaph)2 (ipp = 2-isopropylphenyl, Naph = 1-napthyl). Homoleptic complexes were also prepared with N-benzyl ligands to yield Cu(nacnacBn)2 and Cu(3-succinimido-nacnacBn)2. All complexes were characterized by single-crystal X-ray diffraction. Even bulkier ligands with N-anthrylmethyl, N-mesitylmethyl, or N-methylbenzyl substituents failed to react with Cu(OiPr)2. In the case of nacnacdippCuOiPr, putative nacnacdippCuOiPr decomposed by β-hydride elimination. Heteroleptic complexes [nacnacBnCu(μ-OiPr)]2 and [3-Cl-nacnacBnCu(μ-OiPr)]2 are very highly active rac-lactide polymerization catalysts, with complete monomer conversion at ambient temperature in solution in 0.5–5 min. In the presence of free alcohol, the homoleptic complexes seem to be in equilibrium with small amounts of the respective heteroleptic complex, which are sufficient to complete polymerization in less than 60 min at room temperature. All catalysts show high control of the polymerization with polydispersities of 1.1 and below. The obtained polymers were essentially atactic, with a slight heterotactic bias at ambient temperature and at −17 °C.
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