DIHYDROGEN REDUCTION OF NITROORGANICS, ALKENES, ALKYNES, AND SCHIFF-BASES USING POLYMER-ANCHORED ORTHOMETALATED SCHIFF-BASE COMPLEXES OF PALLADIUM(II) AS CATALYSTS

Complexation of Schiff bases derived from the condensation of aminopol ystyrene and carbonyl compounds, PhCOR (R=H, CH3, C6H5) with palladium (II) acetate results in the formation of acetatobridged, dinuclear ort hopalladated complexes anchored to macroporous polystyrene beads. Hydr ogen activation of the material al 80 degrees C in DMF suspension brin gs to the reduction of coordinated azomethine group with simultaneous replacement of the bridged acetate by H and DMF, producing the corresp onding mononuclear secondary amine complexes. The activated species ar e highly active towards the dihydrogen reduction of aromatic nitro-and carbonyl compounds, alkenes, alkynes, and Schiff bases under normal p ressure at ambient temperature in aprotic solvents like DMF, DMSO, eth yl acetate, and THF. The highest activity was observed with R=H in a D MF medium. Similar polystyrene-based orthometalated secondary amine co mplexes of palladium(II) prepared by alternative methods exhibit compa rable catalytic activities, The same specimen of the catalyst can bs u sed repeatedly for the reduction of the same or different substrates u nder comparable reaction conditions and stored indefinitely without an y loss of catalytic activity. A tentative reduction mechanism has been suggested on the basis of catalyst transformation, Identification of the intermediates at various stages of reaction, and kinetic studies. (C) 1998 Academic Press.