New reactive polymers containing nitrogen functionalities: From asymmetric synthesis to supported catalysis

Several new reactive polymers containing various nitrogen functionalities have been prepared in bead form and tested as catalysts or ligands for reactive moieties in organic synthesis. In particular polymers containing 4-dialkylaminopyridine pendant groups show good to excellent catalytic activities depending on their structure and their microenvironment. Best results are obtained on polystyrene backbones when the catalytic species are removed from the styrene rings by a three carbon spacer. Poly-benzimidazole resins prepared by precipitation polymerization are good ligands for transition metal catalysts used in the catalytic hydrogenation of nitro compounds or olefinic double-bonds. The PBI resins can also be used to prepare a polymeric oxidizing reagent through the binding of Cr(VI); the reagent oxidizes alcohols to the corresponding carbonyls while spent Cr(II) or Cr(III) remains anchored to the polymer. Other polymers containing chiral amino-alcohol pendant groups show useful properties as chiral auxiliaries in the asymmetric reduction of ketones using polymer-complexed lithium aluminium hydride.