Heterogenisation of a Carbonylation Catalyst on Dispersible Microporous Polymer Nanoparticles

The methanol carbonylation catalyst, cis-[Rh(CO)₂I₂]^–, 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 N-methylpyridinium sites for electrostatic attachment of the anionic rhodium(I) complex. The dispersibility of the polymer-supported catalyst material facilitates the use of in situ transmission IR spectroscopy to obtain kinetic data for the oxidative addition of iodomethane to immobilised cis-[Rh(CO)₂I₂]^– (the rate-limiting step of the carbonylation cycle). Remarkably, the oxidative addition proceeds faster than for the homogeneous system (Bu₄N⁺ counter-ion, CH₂Cl₂, 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/CHCl₃, 120 °C). The supported catalyst is easily recovered and is shown to maintain comparable activity upon recycling.