Lewis acids scandium trifluoromethanesulfonate

Rare earth metals and scandium trifluoromethanesulfonates (lanthanide and scandium triflates) are strong Lewis acids that are quite effective as catalysts in... 

Interestingly, salts other than tin(ll) bis-(2-ethylhexanoate) such as scandium and tin trifluoromethanesulfonate [41 3], zinc octoate [44, 45], and aluminum acetyl acetonate [45] were reported to mediate the ROP of lactones. As far as scandium trifluoromethanesulfonate is concerned, the main advantage is the increase of its Lewis acidity enabling the polymerization to be carried out at low temperatures with acceptable kinetics. Later, faster kinetics were obtained by extending the process to scandium trifluoromethanesulfonimide [Sc(NTf2)3] and scandium nonafluorobutanesulfonimide [Sc(NNf2)3] and to other rare earth metal catalysts (metal=Tm, Sm, Nd) [46]. 

Another approach to the "greening of catalysts has been the use of rare-earth compounds known as inflates. The term inflate is an abbreviation for the trifluoromethanesulfonate (SO3CF3) cation. Some typical triflates that have been used in research include the lanthanides, scandium, and hafnium. These triflates act as Lewis acids (electron acceptors) and can, therefore, be substituted for stronger mineral acids (such as sulfuric acid) with undesirable environmental... 

It is a commonplace to say that there has been explosive growth in the use of lanthanides in organic chemistry. For many years, the use of cerium(iv) compounds as oxidants was widespread, but more recently a whole range of other compounds have made their appearance. Thus samarium(ii) compounds are now routinely used as one-electron reducing agents and the use of trifluoromethanesulfonate ( triflate ) salts of scandium and the lanthanides as water-soluble Lewis acid catalysts is widespread. Beta-diketonate complexes and alkoxides have also come into use there are even applications of mischmetal in organic synthesis. 

Rare earth trifluoromethanesulfonates (triflates) are recently developed unique water tolerant and reusable Lewis acids. They may be used in aqueous solution to promote a wide range of organic transformations including C-C and C-heteroatom bond formation and cyclizations (38,39). Scandium trifkite exhibits increased catalytic activity and may be applied in similar transformations (40). Gallium triflate has also been found to be an equally useful catalyst (41). 

Scandium-based Lewis acid catalysts, especially its trifluoromethanesulfonate (Sc(OTf)3), are versatile catalysts that can accelerate a variety of organic reactions even in water as an environmentally benign solvent [48]. Various kinds of polymer-immobilization techniques have been developed as shown below. 

Hachiya, 1. and Kobayashi, S., Aqueous reactions with a Lewis acid and an organometalhc reagent. The scandium trifluoromethanesulfonate-catalyzed allylation reaction of carbonyl compounds with tetraallyltin, /. Org. Chem., 1993, 58, 6958-6960. 

Scandium trifluoromethanesulfonate has been found to be a Lewis acid catalyst for selective cleavage of esters containing a coordinative group adjacent to an ester moiety (Scheme 35). The reaction proceeded under weak acidic conditions at room temperature the catalyst could be recovered and reused. Even a-acyloxy ketones were deacetylated without racemization. A series of lanthanide complexes, Ln N[S020CH(CF3)2]2 3, have been shown to be very effective catalysts for... 

RS Oakes, TJ HeppenstaU, N Shezad, AA Clifford, CM Rayner. Use of scandium tris(trifluoromethanesulfonate) as a Lewis acid catalyst in supercritical carbon dioxide efficient Diels-Alder reactions and pressure dependent enhancement of endo exo stereoselectivity. Chem Commun 1459-1460, 1999. 

The rare-earth salts of trifluoromethanesulfonic acid (triflic acid) are popular reagents for lanthanide-mediated organic reactions. Especially scandium(III) triflate, Sc(CF3S03)3, and ytterbium(lll) triflate, Yb(CF3S03)3, are often used as mild Lewis acids for reactions in water (Kobayashi et al., 2002). It is therefore surprising that only very few studies of cerium(IV)-mediated reactions describe the use of cerium(IV) triflate, Ce(CF3 803)4 or Ce(OTf)4, as a reagent. This salt was first reported by Kreh et al. (1987), who prepared a solution of cerium(lV) in aqueous triflic acid by electrochemical oxidation of a cerium(III) triflate solution. They illustrated the use of this reagent for oxidation of alkylaromatic and polycyclic aromatic compounds. Imamoto et al. (1990) prepared cerium(IV) triflate by reaction... 

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