Carbonylation catalyst immobilization

Studies on the immobilization of Pt-based hydrosilylation catalysts have resulted in the development of polymer-supported Pt catalysts that exhibit high hydrosilylation and low isomerization activity, high selectivity, and stability in solventless alkene hydrosilylation at room temperature.627 Results with Rh(I) and Pt(II) complexes supported on polyamides628 and Mn-based carbonyl complexes immobilized on aminated poly(siloxane) have also been published.629 A supported Pt-Pd bimetallic colloid containing Pd as the core metal with Pt on the surface showed a remarkable shift in activity in the hydrosilylation of 1-octene.630... 

Anionic metal complexes, for example [Rh(CO)2l2], can be exchanged onto the anion-exchange resin Dowex 1-X8. The supported rhodium carbonyl iodide complex functions as an immobilized methanol Carbonylation catalyst. Metal complexes of the water-soluble phosphine TPPTS and its monosulfonated analog have also been exchanged onto anion-exchange resins. The pendant sulfonate groups provide the electrostatic attraction to the support. 

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. 

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. 

An alternative strategy for catalyst immobilization uses ion-pair interactions between ionic catalyst complexes and ion-exchange resins. Because all the rhodium iodocarbonyl complexes in the catalytic methanol carbonylation cycle are anionic, this is an attractive candidate for ionic attachment. In 1981, Drago et al. described the effective immobilization of the rhodium catalyst on polymeric supports based on methylated... 

Our work at Dow has also sought to examine the commercial viability of Rh/10, 11, 12 catalysts for the hydroformylation of a variety of olefins (33). The results that follow were obtained during laboratory and pilot plant studies on the hydroformylation of dicyclopentadiene (DCPD) to dicyclopentadiene dimethanol(DCPDDM) using various Rh carbonyl sources immobilized on 10, 11, and 12. 

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... 

The form and phase of the active catalyst in all of the examples above for liquid-phase carbonylation remain in some doubt. Rates and selectivities appear to be generally similar to the homogeneous system, but there are few comparative data. Convincing evidence for catalyst immobilization under liquid-phase conditions is currently lacking for carbon and zeolite supports. Such evidence could be provided by continuous flow experiments, by direct sampling vmder reaction conditions, or by using in situ techniques such as high pressure infrared spectroscopy in a batch reactor study. 

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. 

In recent years, extensive attention has been focused on finding cultured plant cells that can be used as catalysts for organic functional group transformations. A number of transformations employing freely suspended or immobilized plant cell cultures have been reported.24 For example, Akakabe et al.25 report that immobilized cells of Daucus carota from carrot can be used to reduce prochiral carbonyl substrates such as keto esters, aromatic ketones, and heterocyclic ketones to the corresponding secondary alcohols in ( -configuration with enantiomeric excess of 52-99% and chemical yields of 30 63%). 

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. 

Some successful attempts to immobilize catalysts for the oxidation of alcohols to carbonyl compounds involve the attachment of TEMPO-derivatives to a solid phase. Bolm et al. were the first to immobilize l-hydroxy-2,2,6,6-tetramethylpiperi-dine to modified silica gel (SG-TMP-OH) (11) and applied in the oxidation of multifunctional alcohols [68]. Other groups further investigated the use of polymer-supported TEMPO [69]. This system allowed the oxidation of alcohols to aldehydes and ketones, respectively, using bleach to regenerate the immobilized ni-troxyl radical (Scheme 4.6). 

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]. 

Many other modifications, particularly of the Rh and Mel catalysed carbonylation of MeOH, have been proposed and some of these have been operated commercially or may have been tested at significant pilot plant scale. These include, for example, the use of phosphine oxide species such as PPh30 [20] as promoters and systems involving immobilizing the Rh on ion exchange resins [21]. Numerous examples of ligand modified catalysts have been described, particularly for Rh, though relatively few complexes have been shown to have any extended lifetime at typical process conditions and none are reported in commercial use [22, 23]. The carbonyl iodides of Ru and Os mentioned above in the context of the Cativa process are also promoters for Rh catalysed carbonylation of MeOH to AcOH [24]. 

A phosgene-free route to aromatic isocyanates, such as M DI and TDI, was reported by Fernandez et al. [42] (Scheme 5.7) According to the patent, the one-pot synthesis involves the use of an immobilized Schiff base type of ligand catalyst that facilitates the oxidative carbonylation of aromatic amines to the corresponding isocyanates. However, 2,2,2-trifluoroethanol (TFE), 1,2-dichlorobenzene, and carbon monoxide were used in this process, so this would not be a totally environmentally friendly process even if these reagents could be recycled and reused. 

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. 

---