Sustainable Mizoroki-Heck Cross-Coupling Using a Pd(II)-Polymer as Precatalyst in 1‑Butanol

This work describes the application of a palladium-containing polymeric precatalyst (Pd/PECIm) for the sustainable Mizoroki-Heck (MH) cross-coupling reaction, focusing on the use of green solvents. Building on previous research in which Pd/PECIm was successfully applied to the Suzuki-Miyaura reaction, the cross-coupling between iodobenzene and ethyl acrylate was initially performed in water and 2-propanol (iPrOH). While low yields were obtained in water or iPrOH alone, good yields were obtained in a mixture of both solvents. However, partial polymer degradation was observed, which led to the formation of inactive "palladium black" aggregates, hindering catalyst reuse. The use of 1-butanol (1-BuOH) provided superior efficiency, and under optimized conditions, the system achieved 95% conversion to ethyl cinnamate in just 1.5 h with 0.5 mol% Pd. Imidization of the polymer matrix took place in 1-BuOH, which preserved its structural integrity and allowed for the controlled formation of stable Pd nanoparticles. The catalyst could be reused for at least five cycles. The methodology demonstrated a broad substrate scope, producing various cinnamate and stilbene derivatives with excellent yields, and was successfully scaled up 50-fold with a 93% yield. Overall, Pd/PECIm in 1-BuOH represents an efficient, stable, and environmentally friendly alternative for MH transformations.