Highly selective hydroformylation of vinylarenes to branched aldehydes by [Rh(cod)Cl]2Entrapped in ionic liquid modified silica sol-gel

A co-entrapped mixture of [Rh(cod)Cl](2) and Na[Ph2R-3(C6H4SO3)] within a silica sol-gel matrix modified with ca. 5% of 1-butyl-3-[3-(trimethoxysilyl)propyl]imidazolium chloride catalyzes, in n-heptane, the hydroformylation of a variety of vinylarenes. At 50 degrees C and under 6.9 bar each of H-2 and CO the reaction is high-yielding and highly selective. Non-hindered substrates give >95 % of branched aldehydes and only <5 % of the linear isomers. The ceramic catalyst is leach-proof and recyclable. It does not lose its high catalytic activity and selectivity for at least four runs. The selectivity depends on the pressure of the gases, the temperature and the solvent. The electronic nature has no influence on the selectivity, but the latter is diminished by steric effects. Upon omission of the sol-gel component, the catalyst deteriorates and practically loses its activity after the first half-life of the reaction. In the absence of the ionic liquid, the catalyst undergoes substantial leaching. (C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007).