Recoverable/recyclable catalysts

However, PEG supported metal-free catalysts have also been shown to perform well in water. For example the synthesis of a PEG-supported TEMPO (2,2,6,6-tetramethyl-piperidine-l-oxyl), and its use as a highly efficient, recoverable and recyclable catalyst in oxidation reactions was described (Pozzi et al. 2004). 

In this chapter, we will present some contemporary results from our laboratory aimed toward blending the desirable properties of homogeneous and heterogeneous catalysts to create highly active, selective, and recoverable immobilized catalysts. The chapter covers organometaUic catalytic systems for polymerization reactions as well as small molecule reactions. Formation of single-site catalysts, recyclability, and stability/leaching issues will be addressed, as will studies on the effects of the immobilization procedure and the nature of the support structure on catalytic performance. Finally, a brief discussion on projected future directions for immobilized catalysts is presented. 

M. Benaglia, T. Danelli, G. Pozzi, Synthesis of poly(ethylene glycol)-supported manganese porphyrins Efficient, recoverable and recyclable catalysts for epoxidation of alkenes, Org. Biomol. Chem. 1 (2003) 454. 

Since polymers like 110 or 111 are phase-selectively soluble in the polar phase of a polar/nonpolar biphasic mixture cold and still soluble when the solvent mixture is heated to miscibility, polymers like 77 or 81 can be used as recoverable, recyclable allylic substitution, Heck, or hydrogenation catalysts in Eq. 48, Eq. 49, or 50, respectively. 

Comprehensive Asymmetric Catalysis, Vol. 1, E. N. Jacobsen, A. Pfaltz, H. Yamamoto, eds.. Springer, Berlin, Germany, 1999 See also K. J. Ding, F. J. K. Uozomi, eds. Handbook qf Asymmetric Heterogeneous Catalysts, Wiley-VCH, Weinheim, 2008. M. Benaglia, ed.. Recoverable and Recyclable Catalysts 2009, John Wiley Sons. 

Rostami A, Tahmasbi B, Gholami H, Taymorian H (2013) Supported N-propylsulfamic acid on magnetic nanoparticles used as recoverable and recyclable catalyst for the synthesis of 2,3-dihydroquinazolin-4(l H -oncs in water. Chinese Chem Lett 24 211-214... 

Desset, S. and Cole-Hanulton, D. (2009). Biphasic catalysis catalysis in supercritical CO2 and in water, in M. Benagfia (ed.). Recoverable and Recyclable Catalysts, John Wiley Sons, Ltd, Chichester, pp. 199-257. 

Benaglia, M. (2009) Recoverable and Recyclable Catalysts, Wiley, Chichester, UK. 

Recoverable and Recyclable Catalysts (ed. M. Benaglia), John Wiley Sons,... 

A clean, Strecker-type synthesis of a-aminonitriles has been developed amine, aldehyde, tributyltin cyanide, and scandium(III) triflate (as catalyst) are mixed together at room temperature. Yields for a range of aliphatic and aromatic aldehydes are typically ca 90%, the solvent can be organic or aqueous, the 10% catalyst loading is recoverable and reusable, and the tin reagent is similarly recyclable. 

Interestingly, the dimeric Cr(salen) catalyst 64 supported on silica showed enhanced activity for ARO of 1,2-epoxyhexane and cyclohexene oxide in the presence of ionic liquids particularly with [BMIM][PF6] (64-IL) [86] (Table 6). A significant increase in the product selectivity was also observed with silica supported ionic liquid (64-SILP) for ARO of 1,2-epoxyhexane and cyclohexene oxide (ee, of 87% and 75% respectively) as eompared to silica supported catalyst minus the ionie liquid (Table 6, entries 5,6). However, after repeated recycling, the silica support material deteriorates due to the abrasive forees in the stirred reactor. As a result, silica material was non-recoverable, but the expensive dimeric Cr(salen) catalyst 64 and the ionic liquid was recovered quantitatively by Soxhlet extraction with acetone. SILP-catalyst system was also used in a eontinuous-flow reactor. 

Very reeently Kureshy et al. [98] further reported non-salen chiral Schiff base derived Ti complexes as eatalysts 70, 71 (Figure 23) in the KR of meso-siiXheae oxide, cyclohexene oxide, cyelooetene oxide and cA-butene oxide with anilines. The study deliberated upon the role of several ehiral and achiral additives with these catalysts to give chiral y9-amino alcohols with high enantioselectivity ee, >99%) in excellent yield (>99%) at 0 °C in lOh. Unlike the monomerie version 72 the chiral catalyst 70 used in this study was recoverable and recyclable several times with retention of its performance (Table 10)... 

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