Polymer-supported complexes

If molybdenum(VI) is generated by treatment of a polymer-supported complex containing molybdenum(V) with a hydroperoxide, then this polymer-supported oxidant may also be used to prepare sulphones from sulphoxides. In this case the yield is not good unless the sulphoxide is repeatedly passed through a column containing the oxidant or the reaction is performed by stirring the polymer and the sulphoxide together at 56 °C for 16 hours . ... 

Three generations of dendritic phosphines have been prepared from 3,5-diaminobenzoylglycine and 9-fluorenylmethoxycarbonyl-L-phenylalanine. The dendrimers were then attached to MBHA resin, treated with CH20 and Ph2PH, and converted to their Rh complexes. The polymer-supported complexes are excellent catalysts for the hydroformylation of alkenes, which could be recycled.283 The bidentate diphosphine A,A-bis-(P-(phosphabicyclo[3.3.1] nonan) methyl)aniline was prepared by phosphanomethylation of aniline. It forms a Rh-complex which is a highly regioselective catalyst in the hydroformylation of citronellene.284... 

The most well-developed recent examples of catalysis concern catalysts for oxidation reactions these are essentially achiral or chiral metal-salen complexes. Taking into account a number of results suggesting the importance of a degree of mobility of the bound complex, Sherrington et al. synthesized a series of polymer-supported complexes in which [Mn(salen)Cl] units are immobilized in a pendant fashion by only one of the aromatic rings, to polystyrene or poly(methacrylate) resin beads of various morphology (Figure 6).78,79... 

In subsequent work the same supported catalysts were used in different reactor setups [20] (Figure 3.3). A vapour-phase reactor in which the supported catalyst was mounted on a bed was used for the hydroformylation of volatile alkenes such as cis-2-butene and trifluoropropene. The initial activities and selectivity s were similar to those of the homogeneous solutions, i.e. a TOF of 114 and 90% ee in the hydroformylation of trifluoropropene was reported. No rhodium was detected in the product phase, which means less then 0.8% of the loaded rhodium had leached. The results were, however, very sensitive to the conditions applied and, especially at longer reaction times, the catalyst decomposed. In a second approach the polymer supported complex was packed in a stainless steal column and installed in a continuous flow set-up. 

A similar mechanism almost certainly takes place on polymer-supported complexes. Indeed, some evidence has been put forward for the formation of some platinum(II) species when a styrene/divinylbenzene copolymer bearing dimethylamino groups is treated with chloroplatinic acid (75). 

Pyridinium and quaternary ammonium resins react with chromium trioxide, producing polymer-supported complex chromates that oxidize alcohols, and provide a very facile work-up.427... 

Structural characterisation of polymer supported complexes using EXAFS... 

TiO2/SiO2, Ag-Cu alloys, soft Pt(II) Lewis acids, MTO, oxaziridinium salts, NHPI, polyoxometallates, phase-transfer systems, polymer-supported complexes, calixarene complexes, and biologically based systems. 

S. Bhaduri, H. Khwaja, Polymer-supported complexes. Part 3. Synthesis of a polystyrene-anchored molybdenum(V) dithiocarbamato-derivative and its applications in reactions involving f-butyl hydroperoxide, ]. Chem. Soc., Dalton Trans. (1983) 415. 

For studies on organic transformations with polymer-supported complex catalysts in water, see (a) Uozumi, Y., Danjo, H. and Hayashi, T. (1999) Journal of Organic Chemistry, 64, 3384 (crosscoupling). 

Increasing catalytic activity by augmenting the specific surface area of catalysts with the same selectivity can be explained in two ways either the reaction proceeds in catalyst pores which are large enough not to impose steric hindrances on reagents, or a polymer-supported complex acts as a primary, soluble, catalytically active site where the respective reaction occurs in solution. In the former case, a change in catalytic activity did not result from different diffusion rates of reactants to particular active sites. In the latter case, the activity depended on the readiness with which these sites separate themselves from a polymeric support. In preliminary experiments the authors found that a metal is partially dissolved. 

Decomposition of Water by Polymer-Supported Complex Catalysts... 

In contrast to earlier polymer-supported complex catalysts in which complexes were immobilized through electrostatic interaction, covalent bonds, or coordinative bonds, in this case the complex is captured in Ihe elastomer network by occlusion in a dense polymer in Ihe absence of any supplementary chemical bonding and only as result of steric restrictions. In the hydrogenation of methyl acetoacetate by this catalyst an ee of 70% was obtained in polyethyleneglycol solution at 60 °C. Afer regeneration of the catalyst and reuse, its activity and enantioselectivity were almost unchanged. 

Table 1. Polymer-Supported Complexes for Diene Polymerization... 

In addition, as mentioned above, the polymer-supported complexes possess the bidentate carboxylate group, and the metal-oxygen bonds in these complexes are rich in covalency. For Ziegler-Natta catalysts, one of the requirements for the formation of the active center is the alkylation of the metal ions by exchange between the alkyl group in alkyl aluminum and carboxylate. The covalency of the metal-oxygen bond in the support complex makes this exchange reaction easier. 

They have much higher thermal stability (300 °C) compared to polymer-supported complexes (160°C). Surprisingly, complexing increases the thermal stability in relation to the homogeneous (unanchored) solution. 

Fundamental Research in Homogeneous Catalysis, M. Tsutsui (ed.). Plenum Press, 1979 (Incorporating the Proceedings of the 1st International Conference on Homogeneous Catalysis, Corpus Christi 1978, with some papers on polymer-supported complexes). 

Fischer carbene complexes have proven to be useful in a number of selective syntheses, although the major drawback of these systems is the need for a stoichiometric amount of metal. One way to circiunvent this problem is to employ polymer-boimd complexes that can be recycled. Barluenga et aL [34] prepared polymer-bound Fischer timgsten carbene complexes from the corresponding pentacarbonyl metal compounds The reactivity and reusabihty of the polymer-supported complexes was exemplified by a cyclopropana-tion reaction (Scheme 9). Carbene 11 was heated with methyl acrylate in dichloroethane, and after cooling, saturation with CO, filtration and washing, the polymer 12 could be re-converted to a carbene and recycled. The product of the reaction was a mixture of cyclopropane 13 and C - H inser-... 

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