New Catalyst Immobilization or Recovery Strategies

An easy and simple possibility is the application of water-soluble catalysts in water and an organic phase. The substrate(s) are used as neat liquids or are dissolved in the organic solvent immiscible with water. This protocol is called 

Aqueous biphasic catalysis is also used in homogeneous hydrogenations.117-119 In new examples Ru clusters with the widely used TPPTN [tris(3-sulfonatophenyl) phosphine] ligand120 and Rh complexes with novel carboxylated phosphines121 were applied in alkene hydrogenation, whereas Ru catalysts were used in the hydro-genation of aromatics. Aerobic oxidation of terminal alkenes to methyl ketones was carried out in a biphasic liquid-liquid system by stable, recyclable, water-soluble Pd(II) complexes with sulfonated bidentate diamine ligands.124 

The fluorous biphasic catalysis concept was successfully demonstrated first by hydroformylation of 1-decene carried out in perfluoromethylcyclohexane and toluene, which forms a homogeneous liquid phase at 100°C in the presence of catalyst 2 prepared in situ according to Eq. (14.1) 125,133 

Similar useful characteristics were found for catalysts prepared by fluorous polymer ligands.134 High reaction rates were found for the Rh-catalyzed hydroformylation of higher alkenes with fluoroponytail-modified arylphosphines in supercitical C02.84 

Hydroboration of a variety of alkenes and terminal alkynes with catecholborane in the fluorous solvent perfluoromethylcyclohexane was performed using fluorous analogs of the Wilkinson catalyst.135 136 Recycling of a rhodium-based alkene hydrosilylation catalyst was also successful.137 Activated aromatics and naphthalene showed satisfactory reactivity in Friedel-Crafts acylation with acid anhydrides in the presence of Yb tris(perfluoroalkanesulfonyl)methide catalysts.138 

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