Homogeneous Precious Metal Catalysts for the Pharmaceutical, Agrochemical & Finechemical Industry

Carbonylations are conversions with carbon monoxide (CO) for the formation of aldehydes, ketones, or carboxylic acids by inserting a C=O group.

The most important process on a large scale is the carbonylation of methanol to acetic acid ("Monsanto Process"). Moreover, there are other product routes, e.g. the manufacturing of acetic anhydride from methyl acetate. All these processes are based on rhodium in the presence of iodine-containing compounds. Recent methods are also based on iridium with co-catalysts ("Cativa Process").

Oxidations can be run on a large scale with homogeneous precious metals. The best-known case is the "Hoechst-Wacker" process: The synthesis of acetaldehyde from ethene and oxygen in the presence of the catalyst system Pd/Cu (in aqueous, chloride-containing solutions). Other products can be obtained by varying the solvent, the starting material, or the process parameters, e.g. acetic anhydride and butane-2-one respectively from but-1-ene, or allyl acetate from propene.

In the presence of oxidizing agents, the oxidation of alcohols is feasible by using ruthenium or palladium.

Hydroformylation (oxo synthesis) is the conversion of alkenes into aldehydes with syngas – a mixture of carbon monoxide (CO) and hydrogen (H₂). Low-valent rhodium represents the established catalytic metal which is applied via various compounds or precursors according to the used processes (one phase or two phases, high or low pressure). Rhodium catalysts mainly replaced the former cobalt-catalyzed processes.

Hydrogenations are reactions of unsaturated molecules with hydrogen (H₂). Precious metal compounds of rhodium, ruthenium, or iridium rank with the most effective homogeneous hydrogenation catalysts because of their outstanding selectivity.

Catalysts for hydrogenations are often equivalent to those for hydroformylations, where the reactants H₂ and CO are applied.

Besides, C=O's, C=N's, and alkynes can be hydrogenated. Ruthenium in particular has an affinity for C=O bonds. Hydrogenations of imine groups could effectively be managed with iridium.

Hydrogenations can lead to chiral centers. Like right and left hands, "chiral" molecules of the same constitution (empirical formula, structure) behave like image and mirror-image. Chirality is extraordinarily important for modern active ingredients in life science applications, where almost always only one chiral variant is active. Such "asymmetric hydrogenations" are feasible in a very effective way by using precious metal precursors along with chiral ligands.