Chiral dirhodium catalysts confined in porous hosts

摘要

By immobilising homogeneous chiral catalysts on the inner surface of porous solids, considerations like separability, re-use and selectivity may be addressed simultaneously. Dirhodium carboxamide complexes, Rh_2(MEPY)_4 and Rh_2(BNOX)_4, were attached to the surfaces of MCM-41 and silica through ligand exchange with carboxylic acid functionalised tethers. Their activity was probed in the cyclopropanation of styrene with ethyl and tert-butyl diazoacetate, as well as in the Si-H insertion of dimethylphenylsilane with methyl phenyldiazoacetate. Improvements found in regio- and enantioselectivity are discussed in terms of steric constraints imposed by the surface.