Immobilized catalysts carbonylation reactions

A number of insoluble or immobilized catalysts have been developed and applied to the carbonyl-ene reaction. As is evidenced by the entries below, the enantioselectivities are variable. Sasai23 has utilized a titanium-bridged polymer to effect an enantioselective carbonyl-ene (Equation (14)). A single substrate was examined, and the polymer could be reused up to five times without loss of enantioselectivity in the ene reaction. 

Fyfe et al. (354) have combined 31P and 13C CP/MAS NMR studies first to identify the polymer-immobilized catalyst (Scheme 4, compound ii) formed from the precursor i by treatment with Pd(PPh3)4 and, second, to monitor the carbonyl insertion reaction using 13C-enriched CO to yield iii. The use of isotopically enriched CO was required so as to record meaningful signals above those emerging from the carbon-rich polymer background. 

With unmodified rhodium carbonyl catalyst, a high yield of dialdehyde can normally be achieved. After the reaction, the crude aldehyde is separated from the rhodium by distillation. Because of the two aldehyde groups and the high boiling point of the product, much high-boiling residue is formed too, which is difficult to handle with respect to the recovery of the rhodium. Therefore, a remarkable amount is lost. In order to solve this problem, re-immobilized catalysts were developed and tested especially with this product. At first, it was found that re-immobilized catalysts as well as TPP-modified Rh catalysts could be used, if the rhodium concentration was raised from about 30 to 80 ppm with a reaction time prolonged from 2 to 4 h. 

AstraZeneca published the use of an immobilized transition metal carbonyl complex as a catalyst in the Pauson-Khand reaction [67]. This reaction is known to produce useful products but it also suffers from a number of drawbacks dicobalt octacarbonyl and its analogs are volatile, toxic, and unstable due to loss of carbon monoxide and aerial oxidation. These drawbacks can be avoided by the use of an immobilized metal carbonyl complex (Scheme 13), which is safe and convenient to handle (see also [68]). It offers the additional advantages of being reusable after recovery from the reaction medium and the product becomes less contaminated with metal carbonyl remnants. The reaction was applicable to a wide range of substrates with the exception of tetra-substituted alkenes. A typical reaction of enine 32 to the bicyclic enone 33 is depicted in Scheme 13. 

S. Antebi, P. Arya, L.E. Manzer, H. Apler, Carbonylation Reactions of lodoarenes with PAMAM Dendrimer-PaUadium Catalysts Immobilized on SiOj, Journal of... 

Liquid-Phase Carbonylation. An incentive for the development of immobilized solid catalysts in liquid-phase carbonylation is to retain the chemical characteristics of the soluble industrial catalysts (6) in the Reppe reaction and reduce the problems of corrosion as well as the separation of catalyst from reaction liquor. Various supporting materials such as active carbon, polymers, zeolites, and amorphous inorganic oxides are used to immobilize homogeneous carbonylation catalysts. 

Carbonylation of 1,3-Butadiene. The carbonylation reaction of 1,3-butadiene to 3-pentenoic acid is carried out in acetic acid solution in a batch operation mode at 130°C and 70 atm CO pressure in the presence of Rh(I) catalyst immobilized on activated carbon. HI is used as catalyst promoter. A high selectivity... 

In the 1990, Chauvin and coworkers have introduced ionic liquids (ILs) - especially those derived from the combination of quaternary ammonium salts and weakly coordinating anions - as immobilizing agents for various classical transition metal catalyst precursors in reactions [1]. In particular, these liquids provide more adequate and favorable environment for carbonylation reactions as compared to those performed in classical organic solvents or water. The vast majority of these compounds a) are effectively nonvolatile (most of them exhibit negligible vapor pressure) ... 

The troublesome process of product separation and catalyst recycling in carbonylation reactions using ionic liquids can be considerably simplified by using a solid ionic phase [68,69] or by introducing of an inert solid support [70]. The continuous liquid-phase carbonylation of methanol has been performed using the rhodium carbonyl iodide complex [Rh(CO)2l2] immobilized on a methylpyridinium cation resin [68,69]. The catalytic activity remains constant for the 2000-h operation with virtually no Rh leaching. IL-impregnated silica was used as a solid support for the Monsanto-type catalyst system [Rh(CO)2l2]-BMM [70]. 

In 2013, Bhanage designed and developed an IL-immobilized palladium catalyst 183 and successfully employed in carbonylation reactions, including alkoxycarbonylation, phenoxycarbonylation, and aminocarbonylation ( heme 24) [67]. Alkoxycarbonylation reaction between aryl iodide 184 and alcohol or phenol or amine was performed in an autoclave pressurized with 0.5 MPa of carbon monoxide. Current process would be useful for the utilization of carbon monoxide for synthesis of valuable chemicals from simple starting materials with the use of recyclable catalyst. Furthermore, this catalytic system avoids use of phosphine ligands. The IL-supported palladium catalyst was recycled up to four successive recycles. 

Figure 5.14 Sol-gel immobilized TEMPO is an off-the-shelf alcohol oxidation catalyst. In a biphasic reaction system and in organic solvent it yields carbonyls in water it yields carboxylates.

Alkali-immobile dye-releasing quinone compounds, 19 293-294 Alkali lignins, 15 19-20 Alkali manganate(VI) salts, 15 596 Alkali manganates(V), 15 592 Alkali-metal alkoxide catalysts, 10 491 Alkali-metal alkoxides, effects of, 14 252 Alkali-metal alkylstannonates, 24 824 Alkali-metal fluoroxenates, 17 329-330 Alkali-metal hydrides, 13 608 Alkali-metal hydroxides, carbonyl sulfide reaction with, 23 622 Alkali-metal metatungstates, 25 383 Alkali-metal perchlorates, 18 211 Alkali-metal peroxides, 16 393... 

The selectivity in favor of the desired monobenzylated product was found to be >99% and the immobilized Pt02 was found to be 4-5 times more active than the commercial Adams catalysts. In solution or in immobilized form, the PtOz colloid is effective in the hydrogenation of carbonyl compounds or of olefins. Recently, the heterogeneous catalytic amination of aryl bromides by immobilized Pd(0) particles has been reported [163], Secondary amines such as piperidine and diethyl amine are used in the amination of aryl bromides and the reaction proceeds with good turnover numbers and regio-control. The catalysts can be reused repeatedly without loss of activity or selectivity after filtration from the reaction mixture. 

Oxidation of alcohols to carbonyl compounds is an important reaction. Stoichiometric oxidants such as chromates, permanganates and MO4 (M = Ru, Os) are the commonly used reagents [19a,59,60]. However, they are going out of favour increasingly because they create heavy metal wastes . In view of this, development of environmentally friendly heterogeneous catalysts for alcohol oxidation is very important. In the use of catalytic amounts of transition metal salts or complexes as homogeneous catalysts for the oxidation of alcohols [61-64], separation of the catalyst from the reaction mixture and its subsequent recovery in active form is cumbersome. Heterogeneous catalysts for this kind of reaction are therefore necessary [65]. Clearly, encapsulation and/or immobilization of known... 

In this context, much effort has also been invested in controlling the nuclearity of the catalyst ensemble through the selection of its precursor. One area in which considerable progress has been made involves the adsorption of polynuclear clusters onto supports [33]. Examples involving the immobilization of small, preformed polynuclear clusters on supports are the reactions of carbonyl clusters of the late metals [16, 34], the binding of polyoxometalates (POMs) and their neutral alkoxy analogues [35] and heteropolyacids such as the Keggin cluster [36, 37]. 

More than half a century ago it was observed that Re207 and Mo or W carbonyls immobilized on alumina or silica could catalyze the metathesis of propylene into ethylene and 2-butene, an equilibrium reaction. The reaction can be driven either way and it is 100% atom efficient. The introduction of metathesis-based industrial processes was considerably faster than the elucidation of the mechanistic fundamentals [103, 104]. Indeed the first process, the Phillips triolefin process (Scheme 5.55) that was used to convert excess propylene into ethylene and 2-butene, was shut down in 1972, one year after Chauvin proposed the mechanism (Scheme 5.54) that earned him the Nobel prize [105]. Starting with a metal carbene species as active catalyst a metallocyclobutane has to be formed. The Fischer-type metal carbenes known at the time did not catalyze the metathesis reaction but further evidence supporting the Chauvin mechanism was published. Once the Schrock-type metal carbenes became known this changed. In 1980 Schrock and coworkers reported tungsten carbene complexes... 

L-Proline catalyzes the aldol reaction. This approach has been applied to the synthesis of carbohydrate derivatives as illustrated by the glucose derivative 7 (Fig. 11) (237). The three-component Mannich reaction can be used to prepare p-amino and p-amino a-hydroxy carbonyl compounds in a single step (Fig. 12) (233). As with other types of catalysts, organocatalysts can be immobilized to aid recovery (253). 

In a first approximation, the new methods correspond to the conventional solvent techniques of supported catalysts (cf Section 3.1.1.3), liquid biphasic catalysis (cf Section 3.1.1.1), and thermomorphic ( smart ) catalysts. One major difference relates to the number of reaction phases and the mass transfer between them. Owing to their miscibility with reaction gases, the use of an SCF will reduce the number of phases and potential mass transfer barriers in processes such as hydrogenation, carbonylations, oxidation, etc. For example, hydroformylation in a conventional liquid biphasic system is in fact a three-phase reaction (g/1/1), whereas it is a two-phase process (sc/1) if an SCF is used. The resulting elimination of mass transfer limitations can lead to increased reaction rates and selectiv-ities and can also facilitate continuous flow processes. Most importantly, however, the techniques summarized in Table 2 can provide entirely new solutions to catalyst immobilization which are not available with the established set of liquid solvents. 

Hvdro en tion of Ethylene. This test reaction has been ran under a variety of activation conditions. Catalysts derived from Cr(CO)g, Mo(CO)g, W(CO)6, Ru3(CO).2. Os (CO)l2. and the Fe carbonyls have been found to be at least 10-fold more active than their traditional counterparts. The dichotomy between the more difficult to reduce metals and those easier to reduce is beautifully exemplified by the data in Tables IV and V. It is seen that catalysts derived from the more difficult to reduce metals show better activity after activation in the 0 region, whereas catalysts derived from more noble metals are more active after a high temperature reduction. It might also be noted that these catalysts are orders of magnitude more active than immobilized carbonyl complexes (16). 

The anion has been also functionalized, and ILs based on metal carbonyls, alkylselenites and functionalized borates have been synthesized.Some of these ILs, bearing relatively simple functional groups, have been used as solvents in selected metal-catalyzed reactions,evidencing that task-specific ILs can favor the activation of the catalyst, generate new catalytic species, and improve the catalyst stability. Moreover, they are able to optimize immobilization and recyclability, facilitate product isolation, and infiuence the selectivity of the reaction. 

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