Heterogeneous catalysts polystyrene

An alternative that has received a great deal of attention in recent years is the immobilisation of a chiral catalyst on a nonsoluble support (polystyrene resins, silica gel, zeolites, etc.), thereby creating a chiral heterogeneous catalyst. Unlike homogeneous catalysts, these supported complexes can be recovered from the... 

There has been considerable recent research interest in the activation of carbon monoxide en route to more complex organic molecules. Among the various reactions that have been investigated and/or newly discovered, the transition metal catalyzed reduction of CO to hydrocarbons (Fischer-Tropsch synthesis) has enjoyed particular attention (l- ). Whereas most of the successful efforts in this area have been directed toward the development of heterogeneous catalysts, there are relatively few homogeneous systems. Among these, two are based on clusters (10,11) and others are stoichiometric in metal (12-17). In this report we detail the synthesis and catalytic chemistry of polystyrene ( ) supported... 

Methylrheniumtrioxide (MTO) can straightforwardly be immobilized using copolymers consisting of polystyrene and polyvinyl pyridine. The authors proposed two possible structures 18 shown in Scheme 4.10. In the presence of H2O2 these catalysts are efficient and selective heterogeneous catalysts for the epoxidation of alkenes. It was shown that their activity is maintained for at least five recycling experiments [23 dj. In analogy to this work, bipyridyl-functionalized mesoporous silica can be employed for the immobilization of MTO [75]. 

Aiming at easier workup conditions, immobilization of several transition metal catalysts, which show activity for the epoxidation of allylic alcohols, on polymer support has been investigated. For example, Suzuki and coworkers incorporated an oxo-vanadium ion into cross-linked polystyrene resins functionalized with iminodiacetic acid or diethylenetri-amine derivatives (Scheme 57), which afforded a heterogeneous catalyst that can promote... 

Since homogeneous catalysts tend to offer fast reaction with high selectivity and heterogeneous catalysts offer ease of separation, it is not surprising that efforts have been made lo combine the advantageous properties of both. One way to effect this combination is to attach the "homogeneous catalysts to the surface of a polymer such as polystyrene. Wilkinson s catalyst, for example, can be treated as follows ... 

The isospecific polymerisation of styrene was first reported by Natta et al. [1,2], They obtained isotactic polystyrene, employing for the polymerisation a heterogeneous catalyst derived from titanium tetrachloride and an alkylaluminium compound. 

When supported on AI2O3 as a carrier, half-sandwich metallocenes such as CpTiCl3 and Cp TiCl3 also gave rise to suitable stereospecific catalysts that could even be activated by Al(z -Bu)3 [69]. However, in contrast to the respective homogeneous catalysts (yielding syndiotactic polystyrene), polymerisation with these heterogeneous catalysts afforded isotactic and syndiotactic polystyrenes. 

The last few decades has seen substantial progress in the fabrication of synthetic polymers with biocatalytic properties. A range of polymers has been examined as structural frameworks for the attachment of catalytic groups. For homogeneous catalysts, highly branched polyethylenimines have proved particularly versatile. Modified polystyrenes have served well as foundations for heterogeneous catalysts. 

A wide variety of heterogeneous catalysts have been tested for the catalytic cracking of polyolefins and polystyrene, which can be summarized as follows ... 

Oxidation of secondary alcohols with catalyzed by methyltrioxorhenium (MTO) as homogeneous catalyst and supported MTO (polyvinylpyridine/MTO and polystyrene/MTO) as heterogeneous catalysts was investigated by Crucianelli et al. [3]. 

Immobilized copper-zeolite Y (Cu-HY) bis(oxazolines) were employed as heterogeneous catalysts in carbonyl-ene and imino-ene reactions, allowing the synthesis of a-hydroxy and a-amino carbonyl compounds 163 from 161 and 162 in satisfactory yields and high enantioselection <04AG(E)1685>. The use of a new, insoluble polystyrene-bound Box ligand (IPB-BOX) was also described with good activity (85-95% ee) <04TA3233>. 

Systems that reduce unsaturated groupings in addition to C=C or C=C, e.g., >C=0, —N=N—, —CH=N—, —N02, are [RhH2(PMe3)2L2]+, where L=solvent, and the complex RhCl3py3 in dimethylformamide solution in the presence of sodium borohydride.57 A phosphorus-containing polystyrene polymer forms a complex with rhodium on treatment with RhCl(PPh3)3 and can act as an efficient heterogeneous catalyst.58... 

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