Analogues of two reported homogeneous hydrogenation catalysts based upon square planar palladium complexes have been prepared with a view to modifying the structures to permit the control of selectivity by micellar interactions. Derivatives of bisacetylacetonatopaIladium( 11) in which the diketone was alkylated at C-3 or C-5 were prepared but no useful catalytic activity was observed for the reduction of nitrobenzene to aniline in the presence of pyridine. Complexes were also prepared from bisacetylacetonatopaIladium( 11) with 4-substituted pyridines as ligands; 4-tridecylpyridine afforded an unstable complex but 4-decylaminopyridine afforded a stable complex with low catalytic activity. A series of salicylidene imine palladium(ti) complexes was prepared. Contrary to previous reports, the well-known salicyclidene-ethylenediaminepalladium( 11) complex was not a catalyst for homogeneous hydrogenation but a new oligomeric green heterogenous complex with selective hydrogenation properties was discovered. This green complex was selective for the hydrogenation of alkynes, especially terminal alkynes, and reduced few other functional groups (ArNO,, ArCHO). Many variations on this structure were investigated in an attempt to discover a soluble or crystalline analogue of the green complex but no complexes with improved properties were isolated.
ChemInform Abstract A green insolulable Pd(II) salen complex is prepared from PdCl2 and bis(salicylidene)ethylenediamine. This complex, the structure of which is not determined yet, is employed as a catalyst in the hydrogenation of alkynes, alkenes, and nitro compounds as shown in the reaction scheme.
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