ABSTRACT
Pradeep Goel, Clementina Reyes, Setrak Tanielyan, and Robert Augustine
Center for Applied Catalysis, Seton Hall University, South Orange, NJ 07079
augustro@shu.edu Abstract In almost all of the previous descriptions of our Anchored Homogeneous Catalysts an alumina was the support used. However, the technique of using a heteropoly acid as the anchoring agent does not limit itself to only alumina as the solid support for these species. Some brief mention has been made of the use of carbon, clay, silica and lanthana as supports but nothing extensive was done with these materials. We report here some examples of the use of carbon supported anchored homogeneous catalysts for the hydrogenation of prochiral substrates at moderate to high substrate/catalyst ratios along with a comparison of these results with those obtained using the corresponding homogeneous catalysts under the same conditions. Particular attention will be paid to the use of the anchored chiral Rh(DuPhos) and Rh(BoPhoz) species in the hydrogenation of dimethyl itaconate. Reaction rates, product enantioselectivities and the extent of metal loss will be presented where appropriate. Introduction Our Anchored Homogeneous Catalysts (AHC’s) are composed of a support material, a catalytically active organometallic complex and a heteropoly acid (HPA) used to anchor the complex to the support. The most common HPA used in our work is phosphotungstic acid (PTA). Previous studies on the use of these AHC’s have been concerned with studying the effect which different reaction variables had on the activity, selectivity and stability of these catalysts (1-9). These reactions were typically run at relatively low substrate/catalyst ratios (turnover numbers-TON’s), usually between 50 and 100. While these low TON reactions made it possible to obtain a great deal of information concerning the AHC’s, in order to establish that these catalysts could be used in commercial applications it was necessary to apply them to reactions at much higher TON’s and, also, to make direct comparisons with the corresponding homogeneous catalyst under the same reaction conditions. Almost all of these reactions used catalysts supported on alumina, but some mention was made of the use of other support materials as well (1-4).
