One-Step Simple Preparation of Catalytic Initiators for Catalyst-Transfer Kumada Polymerization: Synthesis of Defect-Free Polythiophenes

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• 作者：Carlos A. Chavez ; Jinwoo Choi ; Evgueni E. Nesterov
• 刊名：Macromolecules
• 出版年：2014
• 出版时间：January 28, 2014
• 年：2014
• 卷：47
• 期：2
• 页码：506-516
• 全文大小：505K
• ISSN：1520-5835

文摘

Externally initiated living catalyst-transfer polymerization based on Ni(II)-catalyzed Kumada coupling of aromatic halogen-substituted Grignard monomers is an established and highly efficient method for the controlled preparation of conjugated polymers such as polythiophenes and poly(p-phenylenes). In this contribution, we report a simple preparation of external catalytic initiators for such a polymerization based on oxidative addition between a readily available Ni(0) complex Ni(dppp)₂ (where dppp is 1,3-bis(diphenylphosphino)propane) and various aryl halides. As a direct challenge to previous reports and established opinion that such a reaction would be impossible, this clean and efficient oxidative addition enables simple preparation of highly reactive catalytic initiators for the catalyst-transfer polymerization. In particular, we demonstrated that polymerization of 5-halo-2-thienylmagnesium monomers initiated by these catalysts produced highly regioregular, defect-free polythiophenes and block copolymers with high molecular weight and low polydispersity. We also found that the polymers prepared using this catalytic system showed a uniform end-group composition with one end terminated with an aryl group from the catalytic initiator and the other end with Br. The bromine termination could potentially allow further synthetic manipulations with the polymers. Overall, this convenient and advantageous method for the preparation of external catalytic initiators provides a simple and straightforward approach to controlled synthesis of polythiophenes and other conjugated polymers.