Structure and reactivity of polymer-supported carbonylation catalysts

Abstract

The structure and reactivity of anionic complexes [M(CO)₂I₂]⁻, supported on ion exchange resins based on quaternised poly(4-vinylpyridine-co-styrene-co-divinylbenzene) have been investigated using a variety of techniques. Infrared spectroscopy and EXAFS measurements show that the supported complexes adopt square planar structures very similar to those found in solution. The geometrical data obtained by EXFAS are also compared with new X-ray structures of the model compounds, [4-RC₅H₄NMe][Rh(CO)₂I₂] (R = H (1) or Et (2)). The reactivity towards MeI of [M(CO)₂I₂]⁻ supported on thin polymer films was probed directly in situ by IR spectroscopy. For M = Rh, oxidative addition of MeI was followed by rapid migratory CO insertion to give [Rh(CO)(COMe)I₃]⁻, whereas for M = Ir oxidative addition gave a stable methyl complex, [Ir(CO)₂I₃Me]⁻, mirroring the established solution chemistry. The reactions were first order in both [complex] and [MeI] and the observed pseudo-first order rate constants were comparable with those in homogeneous solution, although some subtle cation effects were observed. The kinetic measurements appear to be the first examples of quantitative rate data for fundamental reaction steps of a heterogenised transition metal catalyst.