Immobilized Complexes for Enantioselective Catalysis: the Industrial Perspective

Abstract

Work carried out during the development of a production process for (­S)-Metolachlor, an important herbicide now produced on a >10,000 t/year scale with a homogeneous catalyst, is used as an example to describe the design and preparation of immobilized catalysts in an industrial environment. In the course of this work, a modular approach for the covalent immobilization of catalysts was developed. It is shown that immobilized catalysts with industrially relevant properties can indeed be prepared but that these catalysts tend to be substantially more complex and expensive than their homogeneous counterparts. The second part addresses the question of which requirements an immobilized catalyst must meet to be of industrial interest. Different methods for the preparation of catalysts that can be separated by filtration or extraction are discussed and assessed from our personal point of view and experience. It is shown, that to be accepted, immobilized catalysts must have a clear advantage over their homogeneous counterparts and that the immobilization strategy has to be tailored to the type of product as well as to limitations in time and money to be spent. It is concluded that the most feasible method for the immobilization of chiral catalysts is adsorption on suitable solid supports.