Heterogenisation of a Carbonylation Catalyst on Dispersible Microporous Polymer Nanoparticles

Abstract

<div>The methanol carbonylation catalyst, <i>cis</i>-[Rh(CO)<sub>2</sub>I<sub>2</sub>]<sup>–</sup>, has been heterogenised within a dispersible microporous polymer support bearing cationic functionality. The microporous polymer has a core-shell structure in which the porous and insoluble core (a co-polymer of divinylbenzene and 4-vinylpyridine) is suspended in solution by long hydrophilic poly(ethylene glycol) chains, allowing a stable suspension of the nanoparticles to form. Incorporation of 4-vinylpyridine as a co-monomer allows post-synthetic modification to generate <i>N</i>-methylpyridinium sites for electrostatic attachment of the anionic rhodium(I) complex. The dispersibility of the polymer-supported catalyst material facilitates the use of <i>in</i> <i>situ</i> transmission IR spectroscopy to obtain kinetic data for the oxidative addition of iodomethane to immobilised <i>cis</i>-[Rh(CO)<sub>2</sub>I<sub>2</sub>]<sup>–</sup> (the rate-limiting step of the carbonylation cycle). Remarkably, the oxidative addition proceeds faster than for the homogeneous system (Bu<sub>4</sub>N<sup>+</sup> counter-ion, CH<sub>2</sub>Cl<sub>2</sub>, 25 °C). The polymer-supported catalyst was found to be active for methanol carbonylation, with a turnover frequency similar to that of the homogeneous analogue under the same conditions (10 bar CO, MeI/MeOH/CHCl<sub>3</sub>, 120 °C). The supported catalyst is easily recovered and is shown to maintain comparable activity upon recycling.</div>