Synthesis and Characterization of Amine-Bridged Bis(phenolate) Yttrium Guanidinates and Their Application in the Ring-Opening Polymerization of 1,4-Dioxan-2-one

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• 作者：Tinghua Zeng ; Yaorong Wang ; Qi Shen ; Yingming Yao ; Yunjie Luo ; Dongmei Cui
• 刊名：Organometallics
• 出版年：2014
• 出版时间：December 8, 2014
• 年：2014
• 卷：33
• 期：23
• 页码：6803-6811
• 全文大小：492K
• ISSN：1520-6041

文摘

A series of neutral yttrium guanidinates supported by an amine-bridged bis(phenolate) ligand were synthesized, and their catalytic behaviors for the ring-opening polymerization of 1,4-dioxan-2-one (p-dioxanone, PDO) were explored. Metathesis reactions of amine-bridged bis(phenolate) yttrium chlorides LLnCl(THF) [L = Me₂NCH₂CH₂N{CH₂-(2-OC₆H₂-tBu₂-3,5)}₂] with corresponding lithium guanidinates generated in situ in a 1:1 molar ratio in THF gave the neutral yttrium guanidinates LY[R₂NC(NR¹)₂] [R¹ = 鈭扖y, R₂N = 鈭扤(TMS)₂ (1), 鈭扤iPr₂ (2), 鈭扤(CH₂)₅ (3); R¹ = 鈭?i>iPr, R₂N = 鈭扤iPr₂ (4) 鈭扤Ph₂ (5))]. These complexes were well characterized by elemental analyses, IR, and NMR spectroscopy. The definitive molecular structures of these complexes were determined by single-crystal X-ray analysis. It was found that these complexes can efficiently initiate the ring-opening polymerization (ROP) of PDO, and the catalytic activity is affected by the nature of the guanidinate groups with the active sequence of 1 > 2 鈮?3 鈮?4 > 5. The influences of reaction conditions such as polymerization time, polymerization temperature, and molar ratio of monomer to initiator on the polymerization were also investigated. The polymerization kinetics of PDO catalyzed by complex 1 is first-order with respect to monomer concentration, and the apparent activation energy amounts to 30.8 kJ mol^鈥?. The mechanistic investigations showed that the ROP of PDO proceeded through a coordination鈥搃nsertion mechanism with a rupture of the acyl鈥搊xygen bond of the monomer. MALDI-TOF mass spectrum analysis of the oligomer revealed that there are two kinds of polymer chains in this catalytic system, e.g., the linear chains H鈥揫OCH₂CH₂OCH₂CO]_n鈥揙H and the PPDO macrocycles.