Supported Transition Metal Complexes as Catalysts

Abstract

Publisher Summary For many years, most of the intentionally used catalysts were heterogeneous and in which reaction was promoted by the adsorption of some or all of the reactants on the catalyst surface. Catalysis occurs through the formation of intermediate compounds. The major disadvantage of homogeneous catalysts is the problem of separating the very expensive catalyst from the products at the end of the reaction. Distillation is inevitably an endothermic process and is, therefore, expensive. Homogeneous catalysts have the advantage over heterogeneous catalysts of being totally reproducible, because they have a definite stoichiometry and structure. The thermal stability of heterogeneous catalysts––such as pure metals and metal oxides––is often much higher than that of homogeneous catalysts. The use of fluid-bed catalysts represents an attempt to homogenize heterogeneous catalysts. Polystyrene resins with a range of substituents other than tertiary phosphines have been used as supports. The reaction of a metal complex with a support accompanied by the reduction of the metal to a lower oxidation state has been used to prepare supported rhodium and platinum catalysts. Hydroformylation literally involves the addition of a hydrogen atom to one end of an olefinic double bond and a formyl group to the other. Both the rhodium and the cobalt complexes catalyze olefin isomerization, as well as olefin hydroformylation. The formation of alcohols as an end product is promoted by using more vigorous conditions for both the cobalt and rhodium catalysts.