Enantioselective Catalysis, XII. Synthesis of Bis(phosphane) Palladium and Rhodium Complexes on a Polyethylene Oxide Grafted Polystyrene Matrix (TentaGel) and the Catalytic Behavior of the Rhodium Complexes

A new polymer-attached rhodium catalyst on a polyethylene oxide-grafted styrene matrix (TentaGel) is described. The corresponding anchor molecules were prepared by starting from different Boc-protected chiral pyrrolidinebis(phosphane)Pd complexes. The crystal structure of [3R,4R)-N-(4-carboxybutanoyl)-3,4-bis(diphenylphosphanyl)pyrrolidine-P,P′]-diiodopalladium (1c) was determined. The formation of an amide bond between TentaGel and anchor molecules resulted in polymer-bound Pd bisphosphane complexes. De-complexation of the Pd with cyanide and reaction of the free polymeric ligand with [Rh(COD)2]BF4 led to the active hydrogenation catalyst. The influence of different solvents on the swelling volume and the catalytic behavior was tested. The polymer-bound rhodium complex [(3R,4R)-N-(1,5-dioxo-5-TentaGel-amino-pentyl)-3,4-bis (diphenylphosphanyl)pyrrolidineP,P′] (1,5-cyclooctadiene)rhodium tetrafluoroborate (7) has about the same catalytic activity and enantioselectivity as the homogeneous complex [(3R,4R)-N-(tert-butoxycarbonyl)-3,4-bis(diphenylphosphanyl)pyrrolidine-P,P′] (1,5-cyclooctadiene)rhodium tetrafluoroborate (9) in the same solvent mixture. It is possible to reuse 7 once, then it abruptly loses activity. This behavior remains to be clarified.