Rhodium zeolites hydroformylation

For hydroformylation over cobalt and rhodium zeolites the active species have not been defined. However, in the case of RhNaY the in situ formation of a rhodium carbonyl cluster has been identified (226) by infrared spectroscopy. Interestingly, this cluster appears to be different from known compounds such as Rh4(CO)12 and Rh6(CO)16. This does suggest that alternative carbonyl clusters may possibly be formed in zeolites due to the spatial restrictions of the intracrystalline cavities. The mechanism of hydroformylation in these zeolites is probably similar to that known for homogeneous catalysis. 

Table 1.4.1 Kinetic parameters for the simultaneous hydroformylation and hydrogenation of propene over a rhodium zeolite catalyst at 7" = 423 K and 1 atm total pressure [from Rode et al., J. Catal., 96 (1985) 563].

The authors also claimed that the zeolite catalyst exhibited unusually high selectivity to dialdehydes (60%) in the hydroformylation of 1,5-hexadiene. Unfortunately, comparative data obtained under similar conditions with homogeneous rhodium carbonyl catalysts were not presented. 

The application of zeolite-entrapped rhodium carbonyl clusters [prepared by exchanging Rh(NH3)6Cl3 into NaY zeolite followed by reduction in (CO H2) mixtures] as catalysts for the liquid-phase hydroformylation of alkenes has been discussed. More recently, infrared spectra of Rh6(CO)i6, supported on NaY zeolite by sublimation and treated with carbon monoxide at 100 C, have been found to be virtually identical to those obtained in the hydroformylation experiments. ... 

Hydroformylation of olefins was also shown to be catalyzed by rhodium and iridium carbonyls in zeolites. Mononuclear as weU as polynuclear carbonyls are selective towards hydroformylation versus hydrogenation and rhodium carbonyls are more selective. 

The formation and reactivity of catalytically important intra-zeolite rhodium carbonyls have been investigated in some detail [270-276]. Such materials are of interest as catalysts in hydroformylation [277, 278] and water-gas shift [279] reactions. 

NaY zeolite containing [Rhc(CO)i ] has been shown to be a catalyst for the hydro-formylation of alkenes in the liquid phase at 80 C and 80 bar. [38] The catalysts were selective for the formation of butyraldehydes, with a n- to uo-butyraldehyde ratio similar to that shown by mononudear rhodium carbonyls in solutions. [119] The catalyst was also tested for the hydroformylation of nonconjugated dialkenes and produced mainly dialdehydes. [38] The catalyst was recovered after use by decantation and reused with only a small loss in activity. 

By encapsulation of the trialkylphosphine-modified rhodium catalyst into zeolites, the high chemoselectivity was maintained but the Hb ratio in the product alcohol could be increased by as much as 10 times [65]. Anchoring of trialkylphos-phines to carbosilane dendrimers based on polyhedral silsesquioxane (POSS) produced dendrimeric ligands, which in the hydroformylation-hydrogenation of 1-octene preferentially produced linear alcohols. Regioselectivity exceeded that achieved with the low molecular ligand [66]. 

Hetorogenized Catalysts.—Reaction of [Ru(NH3)60H] + with a Faujasite-type zeolite gives a supported Ru complex, which effects hydroformylation of ethylene the catalytic species may be ruthenium clusters that are trapped in the zeolite cages. The effect of reaction conditions upon the selectivity of the hydroformylation of methyl methacrylate with [RhH(CO)(PPh3)3] or its polymer-anchored analogue has been investigated and hydroformylation of hex-l-ene and cyclo-octa-1,5-diene has been carried out with cobalt, rhodium, and platinum-tin complexes anchored to an ion-exchange resin via quaternary amino-phosphines. ... 

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