Syndiotactic and Helix-Sense-Selective Polymerization of Diazoacetates by Rh/Organoamine Catalysis

Abstract

Rh-mediated diazoacetate polymerization has garnered significant attention as an effective approach to obtain highly syndiotactic, completely functionalized carbon chain polymers. However, improving catalytic efficiency of the Rh complex by using readily available reagents remains challenging. Herein, we report an unprecedented catalytic system consisting of RhI(cod)Cl]2 (cod = 1,5-cyclooctadiene) and organoamine that can polymerize various diazoacetates to afford well-defined syndiotactic polycarbenes in high yields, with large molar masses and narrow dispersities. A combination of thorough mechanistic characterization and DFT calculations reveals that the chain propagation may start with [(cod)RhI-H(NEt3)] species, formed by the oxidative addition of [(cod)RhI-Cl(NEt3)] with trace ethanol in reaction solvent and subsequent reductive β-H elimination. Optically active helical polymers also form from achiral bulky diazoacetates when enantiomerically pure amines serve as ancillary reagents. Those polymers without traditional luminophore exhibit interesting circularly polarized photoluminescence. The present work demonstrates a promising route to explore high-performance Rh-based catalysts for carbene polymerization and develop advanced functional materials.