Abstract
Abstract Different approaches were investigated to achieve separation of osmium species from products in the course of the asymmetric dihydroxylation (AD) reaction. Prerequisite for these examinations was the development of a routine method for the detection of electrophilic osmium species in organic product solutions. For recycling of the catalyst an osmium alkaloid complex was immobilised by introducing an ionic group into the ligand and embedding the catalyst in a polyelectrolyte matrix. In addition, the native polymeric aminosugar chitin was used as ligand as well as a support in the dihydroxylation for the first time. These chitin-based catalysts showed good productivities and retention of osmium from the products was ensured using NMO as the oxidant. However, the catalytic reaction did not proceed enantioselectively. Enantiomerically enriched diols were obtained in high yields without significant contamination of osmium applying a homogeneous AD with bleach as the oxidant with a downstream separation of the 1,2-diol from the catalyst by extraction. The remaining osmium-containing solution has been recycled up to eight times without loss of activity and enantioselectivity.
Published Version
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