Palladium catalysts coordination polymers

Entrapment or intercalation of metal species in pores and cavities of solid supports has frequently been used for the immobilization of catalysts in inorganic materials such as zeolites, clays, charcoals, silicas, aluminas, and other solids. Though this review article focuses on the immobilization of palladium complexes on polymer supports via covalent and/or coordination bonds, recent novel approaches to polymer-supported palladium species (including palladium nanoparticles) via nonbonding immobilization, such as encapsulation and incarceration, are intriguing because of their high potential for utility. In this section, several representatives are introduced. 

Generally, the activities of polymer-bound palladium catalysts are less than those of unsupported ones, but here too there are exceptions. Kaneda et al reported that PdCl2, on phosphinated polystyrene was more active than the homogeneous situation.Rates were very solvent dependent— hydrogenation of styrene was slow in dimethyl sulfoxide optimum activity was obtained in solvents of moderate coordinating ability (see Table 6). 

Nickel and palladium react with a number of olefins other than ethylene, to afford a wide range of binary complexes. With styrene (11), Ni atoms react at 77 K to form tris(styrene)Ni(0), a red-brown solid that decomposes at -20 °C. The ability of nickel atoms to coordinate three olefins with a bulky phenyl substituent illustrates that the steric and electronic effects (54,141) responsible for the stability of a tris (planar) coordination are not sufficiently great to preclude formation of a tris complex rather than a bis (olefin) species as the highest-stoichiometry complex. In contrast to the nickel-atom reaction, chromium atoms react (11) with styrene, to form both polystyrene and an intractable material in which chromium is bonded to polystyrene. It would be interesting to ascertain whether such a polymeric material might have any catal3dic activity, in view of the current interest in polymer-sup-ported catalysts (51). 

Note 2 Examples of polymer-supported catalysts are (a) a polymer-metal complex that can coordinate reactants, (b) colloidal palladium dispersed in a swollen network polymer that can act as a hydrogenation catalyst. 

This discovery of the combined importance for high catalyst activity of biden-tate ligands and weakly coordinating anions around a cationic palladium(II) center has, for the first time, given access to efficient synthesis of polyketones. These new catalysts opened the way to economically attractive production and, equally important, provided much more stable polymers with catalyst residues now measured in parts per million rather than percentages. Polyketone thermoplastics have been developed to be easily melt-processable, and could therefore be shown to exhibit a unique set of desirable engineering thermoplastic properties [2]. 

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