Anchored homogeneous catalysts: high turnover number applications

We have recently described a novel catalyst system comprised of a homogeneous complex anchored to a solid support using a heteropoly acid as the anchoring agent. This type of arrangement is particularly effective for anchoring en antioselective homogeneous catalysts since the catalytic species is attached to the support through the metal atom of the complex so no modification of the chiral ligand is needed. In the interest of obtaining as much information as possible in a reasonable time, almost all of the previously reported work involved reactions with substrate: catalyst ratios near 100 recognizing, though, that reactions with such low S:C ratios are not indicative of commercially important processes. We report here a number of dimethyl itaconate hydrogenations over the anchored complexes, Rh(DuPhos), Rh(Skewphos) and Rh(BoPhoz). which have been run as multiple batch processes using the same catalyst. The turnover numbers (TONs) in these reactions ranged from 1000 to 150 000. Analyses of many of these reaction mixtures showed that the amount of Rh was present at less than I ppm levels. frequently much less. (C) 2004 Elsevier B.V. All rights reserved.