Aluminum Complexes Bearing N-Protected 2-Amino- or 2-Imino-Functionalized Pyrrolyl Ligands: Synthesis, Structure, and Catalysis for Preparation of Pyrrolyl-End-Functionalized Polyesters

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• 作者：Yun Wei ; Shaowu Wang ; Xiancui Zhu ; Shuangliu Zhou ; Xiaolong Mu ; Zeming Huang ; Dongjing Hong
• 刊名：Organometallics
• 出版年：2016
• 出版时间：August 22, 2016
• 年：2016
• 卷：35
• 期：16
• 页码：2621-2629
• 全文大小：475K
• 年卷期：0
• ISSN：1520-6041

文摘

Reactivity of N-protected 2-amino- or 2-imino-functionalized pyrroles with aluminum alkyls was investigated, resulting in the isolation of a series of aluminum alkyl complexes. Treatment of 2-imino-functionalized pyrrole with AlMe₃ produced only imino-coordinated aluminum complex 1-Bn-2-(2,6-ⁱPr₂C₆H₃N═CH)C₄H₃NAlMe₃ (1), while reactions of N-protected 2-amino-functionalized pyrroles with aluminum alkyls produced the aluminum alkyl complexes {[η¹-μ-η¹:η¹-1-R₁-2-(2,6-ⁱPr₂C₆H₃NCH₂)C₄H₂N]AlR}₂ (R₁ = Bn, R = Me (2); R₁ = Bn, R = Et (3); R₁ = R = Me (4); R₁ = Me, R = Et (5)), bearing 3-carbon bonded pyrrolyl ligands via C–H σ-bond metathesis reaction. Further reactions of complexes 2–5 with a stoichiometric amount of isopropyl alcohol (ⁱPrOH) afforded the corresponding aluminum alkoxide complexes [1-R₁-2-(2,6-ⁱPr₂C₆H₃NCH₂)C₄H₃NAlR(μ-OⁱPr)]₂ (R₁ = Bn, R = Me (6); R₁ = Bn, R = Et (7); R₁ = R = Me (8); R₁ = Me, R = Et (9)) through selective cleavage of the Al–C (Pyr) bonds. The solid-state structures of the aluminum complexes 1–6 and 8 were confirmed by an X-ray diffraction study. These aluminum alkyl complexes exhibited notable activity toward the ring-opening polymerization of ε-caprolactone and l-lactide in the absence of alcohol. The end group analysis of the ε-CL oligomer gave strong support that the polymerization proceeded via a coordination–insertion mechanism involving a unique Al–C (Pyr) bond initiation, providing pyrrolyl-end-functionalized polyesters.