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Synthesis and reactivity of dinucleating di(diamino)phenolate ligands for enforcing cooperativity Zhai, Xiaofang

Abstract

A new single-frame dinucleating di(diamino)phenolate ligand L has been synthesized and fully characterized, and its coordination chemistry with zinc precursors featuring ethyl, alkoxide, acetate and amide leaving groups has been investigated. Reaction of ligand L with diethyl zinc and Zn[N(SiMe₃)₂]₂ led to the formation of a trinulcear zinc complex 1 (L)Zn₃(CH₂CH₃)₄ and a dinuclear zinc amide complex 4 (L)Zn₂[N(SiMe₃)]₂, respectively. Deprotonation of ligand L followed by salt metathesis with Zn(OAc)₂ gave rise to a trinuclear zinc complex 3 [(L)Zn₃](μ-OAc)₄. The alkyl zinc complex 1 reacted with benzyl alcohol to afford a dinuclear alkoxy zinc complex 2. Complexes 1-3 were fully characterized by ¹H-NMR, ¹³C{¹H}-NMR, COSY, NOESY, HSQC and HMBC NMR spectroscopy and elemental analysis. The solid-state structures of Zn complexes 1-4 were characterized by single-crystal X-ray crystallography. The catalytic activities of complex 1 and 2 towards ring opening polymerization of racemic lactide (rac-lactide) have been studied. Complex 2 showed better control over molecular weight and dispersity than complex 1, and generated heterotactically inclined poly(lactic acid). However, complex 2 promoted extensive transesterification and depolymerization reaction. Complex 3 was found to be active to ROP of rac-lactide at high temperatures and it was active to CO₂/epoxide copolymerization.

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