Polymer supported palladium (II) complexes as hydrogenation catalysts

Dihydrogen reduction of aliphatic and aromatic nitrocompounds, alkenes, aik ynes, nitriles and Schiff bases to their cor­ responding saturated products is eflicient ly ca rri ed out using the soluble and polymer palladium (II) complexes. The immobilization of the palladium (II ) complexes in th e polymer matrix slight ly decreased th e catalytic activities on the basis of metal content but improved the th ermal and chemic al stabi litie s and product se lectiviti es relative to those of the cor­ responding homogeneous ones. The soluble ca talys t has th e propensity to decompose under high pressure, high temperature conditions but the immobilized ones can be used repeatedly and can be stored for long periods without any appreciable loss of cata lyt ic activity. XPS stud y indicates the presence of palladium (II) in the frcsh and used catalyst and a plausible reac ­ tion mechanism has been suggested on the bas is of experimental findings . The study of the activities of transition metal com­ plexes anchored to sol id support has attracted consid­ erable attention during the past two decades. A par­ ticular emphasis on heterogenizing homogeneous catalysts is due to their high industria l and commer­ cial aspects t - 6 . Although a large number of investiga­ tions deal with palladium containing systems as cata­ lysts for hydrogenation 7 - t2 , the study of catalytic ac­ tivities of palladium (II) complexes anchored to polymers are relatively rare l3 t 6 . This may be due to poor chemical , thermal and mechanical properties of the selected polymer materials and tendency of the metal to leave the support on prolonged use I8 - 19 • Plclti­ tJum and palladium complexes anchored to polyvinyl pyridine 20 or polymeric diphenyl benzyl phosphine 2l , rhodium and palladium complex of anthrani lic acid anchored to polystyrene 22 and palladium complex of polyacrylonitrile supported on sil ic a 23 are among the few successfu l catalysts used for the hydrogenation of organic substrates. The choice of the ligand to be an­ chored is usually based on the idea of creat ing envi­ ronments analogous to those in the most ac tive homo­ geneous cata ly sts. With this idea, investigation of the catalyti c act ivity of palladium (II) ani line complex both in homogeneous and heterogeneous phases was carried out.