Supported complex

The concept of supported ionic liquid catalysis involves the surface of a support material that is modified with a monolayer of covalently attached ionic liquid fragments. Treating this surface with additional ionic liquid results in the formation of multiple layers of free ionic liquid on the support material. These layers serve as the reaction phase in which a homogeneous hydroformylation catalyst was dissolved. The concept of supported ionic liquid catalysis has successfully been used for hydroformylation reactions ]81]. 

Rhodium-complexed dendrimers supported on a resin were evaluated as catalysts for the hydroformylation of aryl olefins and vinyl esters. Up to 99% yields and an outstanding selectivity for the branched aldehydes (up to 38 1) were obtained at room temperature and 69 bar CO H2 = 1 1. The dendritic catalysts were recycled by simple filtration and reused even up to the 10th cycle without any loss of activity and selectivity ]82]. 

Si02-tethered rhodium complexes, derived from Rh(CO)2(acac) and 3-(mercapto) propyl- and 3-(l-thioureido)propyl-functionalized silica gel, were used as catalysts in the hydroformylation of various vinyl arenes and vinyl acetate. Conversions, che-moselectivity, and regioselectivity obtained with the Si02-tethered catalysts were comparable with those of the well-known homogeneous rhodium catalysts [85]. 

A rhodium(I) diphosphane complex, [Rh(43)(COD)]Cl, anchored on functionalized carbon support was tested as a catalyst for the hydroformylation of 1-octene. It was found that the catalyst shows an outstanding behavior, being fully active and with almost constant selectivity to the linear aldehyde in four consecutive catalytic runs [86]. 

Exchanging the Rh/TPPTS complex with an anion exchange resin resulted in a stable heterogenized catalyst for the hydroformylation of alkenes. The kinetics of hydroformylation of 1 -hexene using this catalyst was investigated. The rate was found to be first-order dependent on the catalyst, 1-hexene concentration, and H2 partial pressure. A maximum in the rate with increasing partial pressure of carbon monoxide was observed [87]. 

In another system [118], a prochiral sulfide is chemically converted into an optically active sulfoxide with appreciable enantioselectivity (ee 80%) upon reaction on the surface of a clay-ehelate adduct, A-tris-(l,10-Phenanthroline) nickel(II)-montmorillonite. The sulfide is added to a mixture of methanol/water (3 2) and is absorbed by the adduct. Under these conditions, the oxidation is effective with sodium periodate at room temperature in excellent yield (range of 80-90%) (Table 1.6). 

In 1992, a montmorillonite catalyst was used by Choudary et al in another catalytic system for selective oxidation in a liquid phase reaction [119]. A vanadium pillared clay (V-PILC), which was prepared by refluxing VOCI3 in benzene with H-montmorillonite, was used as the catalyst. The solid was filtered, and the resulting clay was found to have 14% of its weight of intercalated vanadium. x-Ray analysis showed an increase in dimensions of montmorillonite 

Various compounds containing V2O5 and other supported phases such as alumina or silica have been compared with (V-PILC), but only poor performance has been found. 

In summary, these catalytic systems can provide efficient methods for sulfoxidation with the advantages of high activity, selectivity, reusability, short reaction time, and enantioselectivities which are not neghgible and which in principle can be improved with further research. 

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In the case of solid supports, the immobilization methods can be classified according to the support-complex interaction. However, this is not a simple classification given that more than one interaction can be present and it is often difficult to discern which interaction is the most significant in terms of immobilization. In this review, however, we have distinguished three categories of interaction [4] (Fig. 1) ... 

In principle this is the method that gives rise to the strongest support-complex interaction. We have considered in this category all the methods in which the support compensates for at least one of the charges of the complex, usually due to the metal, although without considering the exact nature of the metal-support bond, i.e., purely ionic or polarized covalent. In any case, the only possible covalent bond between support and complex would be estabhshed with the metal center, not with the chiral hgand. 

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 . ... 

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... 

Silica is the most commonly used solid support. Treatment with complexes bearing alkoxy- or chlorosilane functional groups is a common way to generate supported complexes on silica or any inorganic oxide containing surface silanol (Si-OH) groups (Scheme 7.2).23,24... 

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... 

We will describe first the different methods of immobilization of catalysts, and highlight their advantages and disadvantages and their fields of application. We will then examine the properties of such supported complexes for the major classes of catalytic reactions. We will focus mainly on those studies where at least some characterization of the supported catalyst is given, unless the catalytic properties of the described system are outstanding the review is therefore far from being exhaustive. Finally, where possible, we will mention tests of recyclability, which are essential for the supported complex to be as a potential industrial catalyst. 

When supported complexes are the catalysts, two types of ionic solid were used zeolites and clays. The structures of these solids (microporous and lamellar respectively) help to improve the stability of the complex catalyst under the reaction conditions by preventing the catalytic species from undergoing dimerization or aggregation, both phenomena which are known to be deactivating. In some cases, the pore walls can tune the selectivity of the reaction by steric effects. The strong similarities of zeolites with the protein portion of natural enzymes was emphasized by Herron.20 The protein protects the active site from side reactions, sieves the substrate molecules, and provides a stereochemically demanding void. Metal complexes have been encapsulated in zeolites, successfully mimicking metalloenzymes for oxidation reactions. Two methods of synthesis of such encapsulated/intercalated complexes have been tested, as follows. 

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... 

Recently, a series of chiral diphosphines (S. -Me-Duphos, (S. -chiraphos, (R,R)-diop and (+)-Norphos were grafted after an ionic exchange onto Al-MCM-41 134 complexes of the form [Rh(cod)(diphosphine)]+ were tested for the hydrogenation of dimethylitaconate. The supported complex with (S,S)-methyl-Duphos reached an activity for the formation of dimethyl ( -methyl-succinate as high as TON = 4000 with an ee close to 92%. Both (R,R)-diop and (,S S )-chiraphos give lower enantioselectivities (ee = 34% and 47% respectively). With (+)-Norphos, dimethyl-([Pg.457]

Supported palladium catalysts for fine chemicals synthesis are generally based on metal particles. Nevertheless, a few examples are reported of the use of supported complexes as catalysts for the Heck reaction (see Chapter 9.6). Nearly all the possible immobilization methods have been tested for this reaction. 

Since the mid-1980s, there have been numerous attempts to heterogenize a large variety of catalysts. These efforts have so far been only partially rewarded. However, a large amount of knowledge has been accumulated, so that the synthesis of better-supported complex catalysts should be a less unpredictable matter. 

Yermakov, Y. I. Catalysis by Supported Complexes. Elsevier Amsterdam, 1981. 

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. 

Marks TJ, Yang W, Stern CL (1991) Models for organometallic molecule-support complexes. Very large counterion modulation of cationic actinide alkyl reactivity. Organometallics 10 840-842... 

The supported complex [Rh(cod)(POLYDIPHOS)]PF6, obtained by stirring a CH2C12 solution of [RhCl(cod)]2 and Bu4NPF6 in the presence of a diphenyl-phosphinopropane-like ligand tethered to a cross-linked styrene/divinylbenzene matrix (POLYDIPHOS), forms an effective catalyst for the hydrogenation of quinoline (Fig. 16.8) [84]. Under relatively mild experimental conditions (80 °C, 30 bar H2), quinoline was mainly converted to THQ, though appreciable formation of both 5,6,7,8-THQ and decahydroquinoline also occurred (Scheme 16.20). 

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... 

Yu. I. Yermakov, B.N. Kuznetsov, V.A. Zakharov, Catalysis by Supported Complexes, Studies in Surface Science Catalysis, Vol. 8, Elsevier, Amsterdam, 1981. 

The impact of the new activation procedure on the WGS rate, using either Na2C03 or NaOH, on silica-supported complexes at 150 °C, is reported in Table 51 156,163 Coitions 1-1.4 g dried silica-supported catalyst with 1.6 wt% loading of Ru. 

Table 51 Impact of Na2C03 or NaOH activation on silica-supported complexes WGS (mol product/day). T = 150 °C 156,163 for... 

A mechanistic study by Haynes et al. demonstrated that the same basic reaction cycle operates for rhodium-catalysed methanol carbonylation in both homogeneous and supported systems [59]. The catalytically active complex [Rh(CO)2l2] was supported on an ion exchange resin based on poly(4-vinylpyridine-co-styrene-co-divinylbenzene) in which the pendant pyridyl groups had been quaternised by reaction with Mel. Heterogenisation of the Rh(I) complex was achieved by reaction of the quaternised polymer with the dimer, [Rh(CO)2l]2 (Scheme 11). Infrared spectroscopy revealed i (CO) bands for the supported [Rh(CO)2l2] anions at frequencies very similar to those observed in solution spectra. The structure of the supported complex was confirmed by EXAFS measurements, which revealed a square planar geometry comparable to that found in solution and the solid state. The first X-ray crystal structures of salts of [Rh(CO)2l2]" were also reported in this study. 

The stage is then set for a solid-phase synthesis. The monomer to he used in the synthesis is added to the 96 wells in the polyethylene plate. The protecting Fmoc groups are removed from the ends of the pins, and the pins themselves are inserted into the 96 wells. At this point, the monomer in each well reacts with the exposed carhoxylate group on the end of the pin, producing the monomer-support complex (comparable to that present in the first step of resin-head-hased SPS). The 96-pin plate is then removed from the 96-well plate, and the pins are washed and reinserted into a second 96-well plate that contains the second monomer to be added. The 96-pin plate is removed, washed again, and reinserted into a third 96-well plate for the addition of a third monomer. The process is repeated as often as necessary to produce the polymers to be produced in the synthesis. 

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