Lewis recoverable catalysts

Figure 5.31 Comparison of the chemoselectivity for RE-POM catalysts and RE triflates [90]. (Reproduced with permission from C. Boglio, et al., Lanthanide complexes of the monovacant Dawson polyoxotungstate [al-PiWnOei] as selective and recoverable Lewis acid catalysts, Angewandte Chemie International Edition, 2006, 45, no. 20, 3324-3327. Wiley-VCH Verlag GmbH Co. KGaA.)...

TpRu complexes as recoverable Lewis acid catalysts for enantioselective solvent-free cycloaddition reactions (Tp = hy dr otr is (pyr azolyl) borate)... 

Reduction of C=N Bonds Catalyzed by Recoverable Lewis Base Catalysts... 

Figure 32.5 Examples of recoverable Lewis base catalysts.

Chung, T.-C. Supported Lewis Acid Catalysts (on Polypropylene Recoverable and Resuable) In Polymeric Materials Encyclopedia Salamone, J. C., Ed., CRC Press Boca Raton, 1996 Vol. 10, pp. 8093-8100. 

Marshall and Xie have also applied the B-H analog of catalyst 3b to the enantiose-lective synthesis of the spirotetronate subunit of kijanolide [20]. The optimum conditions required a full equivalent of the (recoverable) Lewis acid at -78 °C to -40 °C. Reaction at -10 °C gives a product with a significantly lower ee (Eq. 20). 

Aldol and Michael reactions. This Lewis acid catalyzes aldol and Michael reactions smoothly (20 examples, 66-97% yield), using silyl enol ethers as the donors. The catalyst is recoverable and reusable. 

Recently, a recoverable and reusable catalyst AP-Mg-Os04 was developed by the group of Choudary [44]. It was found that commercially available aerogel prepared AP-MgO has defects sites on the surface, for example Mg sites which are Lewis acids. This situation presents an opportunity to prepare new materials. So, the modified aerogel was prepared via a counterionic stabilization of OSO4 with the... 

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