ABSTRACT
Acknowledgments .............................................................................................................. 646
References .......................................................................................................................... 646
In homogeneously catalyzed processes, catalyst recovery and recycling are necessary in order
to prevent heavy-metal contamination of products and the loss of expensive catalysts.
Transition metals, especially Rh, Pd, and Pt, have become enormously expensive. Addition-
ally, at least for asymmetric catalysis, the chiral organic ligand is even more valuable than the
transition metal. Environmental considerations also dictate that the catalysts must be recov-
ered; metal contamination of product or waste streams obviously must be avoided. Trad-
itional methods for catalyst recovery include distillation of the product from the solution
(only possible for thermally robust catalysts) and decomposition of the catalyst followed by
filtration or extraction [1]. These methods add significantly to the complexity and expense of
the process. The use of heterogeneous or heterogenized catalysts (e.g., polymer-supported
complexes) is of course ideal because of the facility in which they can be separated from the
product stream, but they often suffer from leaching and diminished tunability and selectivity.
There is an industrial example of the use of a heterogenized catalyst, a Rh complex bound
electrostatically to an ion exchange resin for methanol carbonylation, but severe leaching is
observed [2, 3]. Thus there is a need in industry for an alternative method of homogeneous
catalyst use and recovery. The need is met by biphasic catalysis.
