Solid support catalysts polystyrenes

The other main support used for solid base catalysts is polystyrene, which while it does not have a well-defined porous structure, does swell in solvents providing an accessible high surface area on which to carry out reactions. One common method of chemically attaching groups to polystyrene involves incorporation of specific amounts of styrene contain-... 

Immobilized catalysts on solid supports inherently have benefits because of their easy separation from the products and the possibility of recycling. They are also expected to be useful for combinatorial chemistry and high-throughput experimentation. The polystyrene-bound BINAP/DPEN-Ru complex (beads) in the presence of (CH3)3COK catalyzes the hydrogenation of l -acetonaphthone with an SCR of 12 300 in a 2-propanol-DMF mixture (1 1, v/v) to afford the chiral alcohol in 97% ee (Fig. 32.35) [113]. This supported complex is separable... 

The immobilization of phase transfer catalysts on solid substrates allows a clean reaction with no contamination of the products by the catalyst. Insoluble polystyrene matrices have been used as a solid support. The polymer matrix does not affect the velocity of the reaction, apart from steric hindrance with respect to the reagents. In the case of immobilization on modified silica the active centre is linked to the support by an alkyl chain of variable length. This length strictly determines the adsorption capacity of the polar support, which then controls the rate of reaction. A three-phase catalytic system is set up. Two distinct phases, containing reagents, come into close... 

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 catal3d ic activity, in view of the current interest in polymer-supported catalysts (51). 

Immobilized catalysts have been studied in metal-catalyzed living radical polymerization for, in part, easy removal of the catalysts from the products. In most examples, the catalytic metal centers are attached to solid supports, such as silica gel and polystyrene beads, via spacers and/or coordinating ligands (Figure 7). The central metals thus far employed include copper and ruthenium. 

Solid-Supported Surface Catalysis by Metal Complexes. Hong et al. (1987a, b, in press) have prepared a variety of hybrid catalysts between Co(II) phthalocyanine complexes and the surfaces of silica gel, polystyrene-divinylben-zene, and Ti02 and tested these hybrids for catalytic activity with respect to the autoxidation of hydrogen sulfide, sulfur dioxide, 2-mercaptoethanol, cysteine, and hydrazine ... 

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