Scandium tris methide

Preparation of scandium tris(tris(perfluorooctanesulfonyl)methide)... 

Friedel-Crafts acylation. Scandium tris(perfluorobutanesulfonyl)methide is a multipurpose catalyst. Besides promoting Friedel-Crafts reactions, it is also useful in the Diels-Alder reaction and Meerwein-Ponndorf-Verley reduction. 

Scandium tris(perfluorooctanesulfonyl)methide complex was immobilized in a fluorous phase as a recyclable catalyst for Mukaiyama aldol reaction (2). On the other hand, the catalytic activity of scandium could be significantly increased by the use of a continuous flow system compared with a batch system. For example, in per-fluoromethylcyclohexane, the aldol reaction of benzaldehyde withthe trimethylsilyl enol ether derived from methyl 2-methylpropannoate was completed within seconds in the presence of less than 0.1 mol% of Sc(N(S02CgFi7)2]3 [3]. 

Against this background it is important that—quite fitting in this still new millennium— the first catalytic Friedel-Crafts acylations of (still relatively electron-rich) aromatic compounds were reported (Figure 5.35). Trifluoromethane sulfonates ( triflates ) of rare-earth metals, e. g., scandium(III)triflate, accomplish Friedel-Crafts acylations with amounts of as little as 1 mole percent. Something similar is true of the tris(trifluoromethanesulfonyl)-methides ( triflides ) of rare-earth metals. Unlike conventional Lewis acids, the cited rare-earth metal salts can form 1 1 complexes with the ketone produced, but these are so unstable that the Lewis acid can re-enter the reaction. Whether this works analogously for the third catalytic system of Figure 5.35 is unclear. 

Tris(perfluorooctanesulfonyl)methide (5.0 g) was added to a solution containing 10ml acetonitrile, 10 ml water, and scandium acetate (0.25 g). The mixture stirred 5 hours at ambient temperature and then heated to 50°C one hour. The product was isolated as in the aforestated method. Elemental analysis supplied. 

Ishihara, K., Pliraiwa, Y., and Yamamoto, PI. 2000. Homogeneous debenzy-lation using extremely active catalysts tris(triflyl)methane, scandium(IIl) tris(triflyl)methide, and copper(ll) tris(triflyl)methide. Synlett 80-82. 

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