Immobilized Ru catalyst

Space limitations unfortunately preclude a full discussion of two more recent approaches to permanently immobilized Ru catalysts, see (a) Monolithic Materials New High-Performance Supports for Permanently Immobilized Metathesis Catalysts, M. Mayr, B. Mayr, M.R. Buchmeiser, Angew. Chem. 2001, 113, 3957-3960 Angew. Chem. Int. Ed. 2001,... 

Scheme 10.4 Ring-closing metathesis over an immobilized Ru catalyst.

Reaction Characteristics of Immobilized Ru-BINAP Catalysts in Asymmetric Hydrogenation of Dimethyl itaconate... 

Reaction experiments were performed at the substrate to catalyst ratios between 250 and 5000 (Table 1). The immobilized catalyst showed a rather constant values of TOP and enantioselectivity in spite of the increase in the S/C ratio, even though these values were slightly lower than those of the homogeneous Ru-BINAP catalyst. After the reaction, the Ru content in the reaction mixture was measured by ICP-AES and was found to be under 2 ppm, the detecting limit of the instrument, indicating the at Ru metal didn t leach significantly during the reaction. These results show that the immobilized Ru-BINAP catalyst had stable activity and enantioselectivity and that the Ru metal complex formed a stable species on the alumina support. 

Effect of reaction conditions on the asymmetric hydrogenation of dimethyl itaconate over immobilized Ru-BINAP catalyst... 

An immobilized Ru-PyBOx catalyst 56 was synthesized by thermally induced radical copolymerization and used to catalyze the flow cyclopropanation reaction between styrene and ethyldiazoacetate (Scheme 4.79), building on initial work performed in batch [179]. For the flow example, a range of experiments using the starting materials in CH2C12 solution, neat or in scC02 were assessed and the results are summarized in Table 4.2 [180],... 

The homogeneous chiral phosphine/DPEN-Ru catalyst can be immobilized by use of polymer-bound phosphines such as polystyrene-anchored BINAP (APB-BINAP) [57, 98], Poly-Nap [99], and poly(BINOL-BINAP) [100], poly(BINAP) [101]. These complexes hydrogenate T-acetonaphthone and acetophenone with S/C of 1000-10 000 under 8 10 atm H2 to give the corresponding secondary alcohols in 84-98% e.e. The recovered complexes are repeatedly used without significant loss of reactivity and enantioselectivity. Immobilization allows the easy separation of catalyst from reaction mixture, recovery, and reuse. These advantages attract much attention in combinatorial synthesis. 

Polymeric membranes also show potential for application in the area of chiral catalysis. Here metallocomplexes find use as homogeneous catalysts, since they show high activity and enantioselectivity. They are expensive, however, and their presence in the final product is undesirable they must be, therefore, separated after the reaction ends. Attempts have been made to immobilize these catalysts on various supports. Immobilization is a laborious process, however, and often the catalyst activity decreases upon immobilization. An alternative would be a hybrid process, which combines the homogeneous catalytic reactor with a nanofiltration membrane system. Smet et al. [2.98] have presented an example of such an application. They studied the hydrogenation of dimethyl itaconate with Ru-BINAP as a homogeneous chiral catalyst. The nanofiltration membrane helps separate the reaction products from the catalyst. Two different configurations can be utilized, one in which the membrane is inserted in the reactor itself, and another in which the membrane is extraneous to the reactor. Ru-BINAP is known to be an excellent hydrogenation catalyst... 

Pt particles with the IL protects the catalyst from oxidation, which can be utilized to protect air-sensitive catalysts [35]. Further examples of heterogeneous reactions on metal immobilized in porous supports using ILs are Heck C-C coupling on Pd [36] benzene hydrogenation on nanoscale Ru-catalysts [37] selective acetylene hydrogenation on Pd-nanoparticles, for example, dissolved in [BMlM][PFg] [38] and citral hydrogenation on Pd immobilized by different ILs on an active carbon cloth [39]. 

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