Formation of Alternating trans-A-alt-B Copolymers through Ring-Opening Metathesis Polymerization Initiated by Molybdenum Imido Alkylidene Complexes

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• 作者：Hyangsoo Jeong ; Jeremy M. John ; Richard R. Schrock
• 刊名：Organometallics
• 出版年：2015
• 出版时间：October 26, 2015
• 年：2015
• 卷：34
• 期：20
• 页码：5136-5145
• 全文大小：640K
• ISSN：1520-6041

文摘

Ring-opening metathesis polymerization (ROMP) is used to prepare trans-poly(A-alt-B) polymers from a 1:1 mixture of A and B where A is a cyclic olefin such as cyclooctene (A₁) or cycloheptene (A₂) and B is a large norbornadiene or norbornene derivative such as 2,3-dicarbomethoxy-7-isopropylidenenorbornadiene (B₁) or dimethylspirobicyclo[2.2.1]hepta-2,5-diene-2,3-dicarboxylate-7,1鈥?cyclopropane (B₂). The most successful initiators that were examined are of the type Mo(NR)(CHCMe₂Ph)[OCMe(CF₃)₂]₂ (R = 2,6-Me₂C₆H₃ (1) or 2,6-i-Pr₂C₆H₃ (2)). The trans configuration of the AB linkages is proposed to result from the steric demand of B. Both anti-MB and syn-MB alkylidenes are observed during the copolymerization, where B was last inserted into a Mo鈺怌 bond, although anti-MB dominates as the reaction proceeds. anti-MB is lower in energy than syn-MB, does not react readily with either A or B, and interconverts slowly with syn-MB through rotation about the Mo鈺怌 bond. Syn-MB does not readily react with B, but it does react slowly with A (rate constant 鈭? M^鈥? s^鈥?) to give anti-MA and one trans-AB linkage. anti-MA then reacts with B (rate constant 鈭?00 M^鈥? s^鈥? or larger) to give syn-MB and the second trans-AB linkage. The reaction has been modeled using experimental data in order to obtain the estimated rate constants above. The reaction between anti-MA and A is proposed to give rise to AA linkages, but AA dyads can amount to <5%. Several other A and B monomers, initiators, and conditions were explored.