DIHYDROGEN REDUCTION OF NITROORGANICS, ALKENES, ALKYNES, AND SCHIFF-BASES USING POLYMER-ANCHORED ORTHOMETALATED SCHIFF-BASE COMPLEXES OF PALLADIUM(II) AS CATALYSTS
Sm. Islam et al., DIHYDROGEN REDUCTION OF NITROORGANICS, ALKENES, ALKYNES, AND SCHIFF-BASES USING POLYMER-ANCHORED ORTHOMETALATED SCHIFF-BASE COMPLEXES OF PALLADIUM(II) AS CATALYSTS, Journal of catalysis, 173(2), 1998, pp. 268-281
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.