Precious Metal Catalysts for Homogeneous Catalysis
Asymmetrical catalytic reactions are special processes for the selective production of chiral compounds. The company Syngenta synthesizes metolachlor in Switzerland using one of the largest industrial processes that is based on asymmetric catalysis.
The substance is used in the cultivation of corn (maize) and is both a specific herbicide against grasses and weeds and also a fungicide. More than 10,000 tonnes of the product are manufactured per annum. Metolachlor has two chirality elements (a chirality center and a chirality axis) and occurs in four diastereomers; the stereoisomers with an (S)-configured chirality center show significantly greater effectiveness.
Syngenta has developed a process to produce the more effective stereoisomers with a high degree of selectivity. The key step in the process is a selective hydrogenation in which the di-µ-chloro-bis[(cycloocta-1,5-diene)iridium(I)] (Abb. 2) , [Ir(cod)Cl]2, and a chiral ferrocenyldiphosphane ligand are used.