Palladium nanoparticle-embedded polymer thin film “dip catalyst” for Suzuki–Miyaura reaction

Abstract

Hallmarks of a successful catalyst include simplicity of design and low cost of fabrication, high efficiency, facile recovery and extensive reusability, amenability to monitoring between reuses, and ease of scale up. Even though the number of palladium nanoparticle based catalysts reported for the Suzuki–Miyaura reaction has grown exponentially in recent years, the aforesaid criteria are rarely met in a single system. We present a palladium nanoparticle-embedded polymer thin film which functions as a highly efficient and reusable “dip catalyst” for the Suzuki–Miyaura reaction. The multilayer free-standing nanocomposite thin film is fabricated using a simple in situ process through thermal annealing of a spin-coated film of poly(vinyl alcohol) (PVA) containing the palladium precursor. Fabrication parameters of the Pd-PVA film are optimized for enhanced catalyst efficiency. The catalyst is shown to produce very high yield, turn over number and turn over frequency in the prototypical reaction of iodobenzene with phenylboronic acid. The “dip catalyst” film is easily retrieved from the reaction system and reintroduced in successive batches; the high efficiency is retained beyond 30 cycles. The thin film structure enabled convenient catalyst monitoring by spectroscopy and microscopy between reruns. Efficient use of the catalyst up to 5 mmol scale reaction is demonstrated. A simple figure-of-merit is formulated to quantify the catalyst performance, and the present catalyst is evaluated in the context of those reported earlier. Preliminary exploration of the utility of the thin film catalyst in the Suzuki–Miyaura reaction with several substrates as well as in the Heck and Sonogashira coupling reactions is carried out.