Development of Efficient Kumada Catalyst-Transfer Polymerizations: A Rapid Injection NMR Study

Transmetalation is a pivotal step in the Kumada–Corriu cross-coupling reaction, yet its mechanistic details have re-mained relatively unexplored compared to other palladium-catalyzed processes. Herein, we systematically investi-gate how diverse phosphine ligands influence the transmetalation rate, using rapid injection NMR (RI-NMR) to di-rectly monitor formation of cross-coupling product. The study reveals that both ligand electronics and sterics signifi-cantly affect kobs, with electron-rich ligands tending to slow down the reaction and heteroatom-substituted ligands dramatically accelerating transmetalation. Examination of halide effects further highlights the delicate interplay be-tween Pd–X bond polarity and transition-state stabilization, offering practical insights for tuning catalytic efficiency. Eyring analyses on selected ligands underscore the importance of entropic factors in the transition state. Finally, we leverage these kinetic findings to guide synthesis of poly(3-hexylthophene) (P3HT) by catalyst-transfer polymeriza-tion (CTP). Fast transmetalation ligands, such as CPhos, give higher-molar-mass polymers with controlled dispersities, whereas slower ligands afford inferior control. These results collectively emphasize the centrality of transmetalation in dictating overall cross-coupling performance and pave the way for rational design of palladium catalysts for both small-molecule synthesis and advanced polymer applications.