Joos Wahlen

Immobilization of molecular catalysts in supported ionic liquid phases

In a supported ionic liquid phase (SILP) catalyst system, an ionic liquid (IL) film is immobilized on a high-surface area porous solid and a homogeneous catalyst is dissolved in this supported IL layer, thereby combining the attractive features of homogeneous catalysts with the benefits of heterogeneous catalysts. In this review reliable strategies for the immobilization of molecular catalysts in SILPs are surveyed. In the first part, general aspects concerning the application of SILP catalysts are presented, focusing on the type of catalyst, support, ionic liquid and reaction conditions. Secondly, organic reactions in which SILP technology is applied to improve the performance of homogeneous transition-metal catalysts are presented: hydroformylation, metathesis reactions, carbonylation, hydrogenation, hydroamination, coupling reactions and asymmetric reactions.

Recent progress in the immobilization of catalysts for selective oxidation in the liquid phase

Reliable strategies are presented for the immobilization of molecular catalysts for selective oxidation in the liquid phase. Besides classical strategies such as ion exchange or covalent anchoring, new approaches are emerging, e.g. based on supported ionic-liquid phases or on incorporation of the active centre in a coordination polymer or a metal-organic framework.

Heterogeneous vanadium catalysts for racemization and chemoenzymatic dynamic kinetic resolution of benzylic alcohols

Cheap and readily available oxovanadium compounds such as vanadyl sulfate (VOSO4) and vanadium oxide (V2O4) catalyze the racemization of benzylic alcohols in the absence of any additives (e.g., bases or hydrogen mediators) or co-catalysts. The reaction occurs at 80 °C in n-octane as the solvent and does not require anhydrous or oxygen-free conditions. Experiments clearly demonstrated that VOSO4 is a reusable and truly heterogeneous racemization catalyst. Insight into the reaction mechanism was obtained from 18O-labeling experiments, which showed that the formation of carbenium ion intermediates is a key step. The V-catalyzed racemization was combined with a lipase-catalyzed kinetic resolution to give a chemoenzymatic dynamic kinetic resolution of benzylic alcohols. The dynamic kinetic resolution (DKR) proceeds in one pot and does not need additives or specifically designed acyl donors. Under optimized conditions, the DKR process yields the corresponding esters in good chemical yield (>90%) and high optical purity (>99% ee).

Catalytic Hydrogenolysis of Aromatic Ketones in Mixed Choline–Betainium Ionic Liquids

The palladium-catalyzed hydrogenolysis of aromatic ketones to alkylbenzenes was studied in mixtures of ionic liquids to explore the promotional effect of these reaction media. Choline-based ionic liquids displayed complete miscibility with the aromatic ketone substrate at reaction temperature and a clear phase separation of the derived alkylbenzene product at room temperature. Selected ionic liquids were then assessed as reaction media in the hydrogenolysis of aromatic ketones over palladium catalysts. A binary mixture of choline and betainium bis(trifluoromethylsulfonyl)imide ionic liquids resulted in the highest conversion and selectivity values in the hydrogenolysis of acetophenone. At the end of the reaction, the immiscible alkylbenzene separates from the ionic liquid mixture and the pure product phase can be isolated by simple decantation. After optimization of the reaction conditions, high yields (>90 %) of alkylbenzene were obtained in all cases. The catalyst and the ionic liquid could be used at least three times without any loss of activity or selectivity.

23-P-33 - Transfer hydrogenation of unsaturated ketones catalyzed by Al-isopropoxide dispersed on MCM-41

Publisher Summary This chapter discusses the transfer hydrogenation of unsaturated ketones catalyzed by Al- iso propoxide dispersed on MCM-41. Aluminium alkoxides are anchored in the pores of siliceous MCM-41 type materials. The resulting catalysts are used in the hydrogen-transfer reduction of α-β-unsaturated ketones to the corresponding allylic alcohols. The most active material is obtained by the exposure of MCM-41 to a toluene solution of Al(OPr i ) 3 . With benzalacetone as a model substrate, optimum reaction conditions are cyclopentanol (hydride donor), toluene (solvent), and addition of 5A molecular sieve (water trapping).

Lanthanum-exchanged zeolites as active and selective catalysts for the generation of singlet oxygen from hydrogen peroxide.

Lanthanum(III)-exchanged zeolites Beta and USY are active and selective catalysts for the generation of singlet oxygen from H2O2 showing superior activity and oxidant efficiency compared to unsupported La-catalysts, e.g. La(OH)3.

Glycol-modified molybdate catalysts for efficient singlet oxygen generation from hydrogen peroxide

Pretreatment of molybdate-exchanged layered double hydroxides in polyalcohols such as ethylene glycol affords heterogeneous catalysts showing largely improved oxidant efficiency compared to the unmodified materials.

New perspectives for zeolites in fine chemical synthesis

Zeolites can be used as heterogenous catalysts in the production of fine chemicals, as illustrated in the following reactions. With TS-1 and hydrogen peroxide, furans are oxidized to flavor compounds. La-exchanged zeolites are, in combination with hydrogen peroxide, a source of singlet dioxygen. Pd-loaded zeolites are heterogenous Heck catalysts, at the condition that proper pretreatment and reaction conditions are selected. Finally, acid zeolitic racemization catalysts have been successfully combined with a lipase for dynamic kinetic resolution of secondary alcohols.