SUPRAMOLECULAR TRANSITION-METAL CATALYSTS IN 2-PHASE SYSTEMS

The concept of covalently connecting a catalytically active transition metal center with a water-soluble receptor (host molecule) makes a ne w type of supramolecular catalysis possible in which the features of m olecular recognition, phase transfer catalysis and transition metal ca talysis are combined in a single system. The first examples of this pr inciple make use of the commercially available beta-cyclodextrin (beta -CD) as the receptor and rhodium complexes of diphosphanes as the cata lytically active center, these being covalently connected to one anoth er via a spacer. In competitive hydrogenation of certain olefins unusu al degrees of substrate selectivity based on the molecular recognition are observed, not possible by conventional transition metal catalysts . The two-phase (H2O/organic) hydrogenation of nitro-aromatics also is a smooth process with these supramolecular catalysts. They also const itute an unusually active catalyst system for the selective hydroformy lation of higher olefins such as 1-octene in a two-phase system. (C) 1 998 Elsevier Science B.V. All rights reserved.