Scandium complexes tetrahydrofuran

The Lewis acid-promoted reaction of aldehydes with a-substituted allylsilanes forms 3-silyltetrahydrofurans in good to high yields.169-172 The use of homochiral allylsilanes is very valuable for highly diastereo- and enantio-selective syntheses of tri- and tetrasubstituted tetrahydrofurans (Equation (43)). Catalytic asymmetric [3-1-21-cycloaddition of a-substituted allenylsilanes to aldehydes can be achieved by a chiral scandium complex.173... 

The scandium complex Sccp3 has polymeric structure with the Sc( -C5115)2 fragments bonded via bridges. In tetrahydrofuran solution, Sccp3 has... 

SCANDIUM TRICHLORIDE TRIS(TETRAHYDROFURAN) AND 0-DIKETIMINATE-SUPPORTED SCANDIUM CHLORIDE COMPLEXES... 

SgO, cycto-Octasulfur monoxide, 21 172 ScCl303Ci2H24, Scandium(IU), trichloro-tris(tetrahydrofuran)-, 21 139 SeC, Carbon selenide, chromium complex, 21 1, 2... 

ScCI3, Scandium chloride, 22 39 ScCl3Cs, Cesium scandium chloride, 22 23 ScC1303C 2Hm, Scandium(lll), trichloro-tris(tetrahydrofuran)-, 21 139 Sc2CI,Cs3, Cesium scandium chloride, 22 25 SeC, Carbon selenide, chromium complex, 21 1, 2 Se2C, Carbon diselenide, 21 6, 7 Se2NC3H,i, Diselenocaibamic acid, N,N-di-ethyl-,... 

The reaction of di- u-alkyl-bis(cyclopentadienyl) rare earth dialkylaluminum complexes with equimolar amounts of pyridine in toluene at room temperature gives dimeric dicyclopentadienyl rare earth methyl complexes, which are isolated in about 80% yield as air-sensitive crystalline solids. They are stable for short periods up to 150°C, soluble in CH2CI2, hot toluene or benzene, partly soluble in cold toluene or benzene, but insoluble in saturated hydrocarbons (Holton et al., 1976a and 1979c). The similar reaction of the corresponding scandium derivative with pyridine or tetrahydrofuran does not give the bridging dimer, but a monomer with coordinated pyridine or tetrahydrofuran ... 

The first allyl derivative of a rare earth was the complex dicyclopentadienyl allyl scandium, prepared by Coutts and Wailes (1970) from dicyclopentadienyl scandium chloride and allyl magnesium chloride in benzene-tetrahydrofuran. The orange compound shows an NMR spectrum with a singlet for the cyclopentadienyl protons at 5.90 ppm, and a quintet at 7.29 and a doublet at 3.05 ppm for the fluxional allyl group. The fluxional allyl group is also implicated by the IR band at 1475 cm for a delocalized C—C stretching vibration. 

Thus, the reaction in aqueous Cu(N03)2 solution proceeded about 800 times faster than in water alone and 250000 times faster than in acetonitrile. This Lewis-acid-catalyzed aqueous Diels-Alder reaction presumably occurs via a transition state such as 2.50 with bidentate complexation to the metal as shown. In a related study, Kobayashi reported that scandium triflate can be used as a water-tolerant Lewis-acid catalyst for a Diels-Alder reaction in (9 1) tetrahydrofuran-water (THF-H2O) [30], though this mixed solvent system cannot take advantage of the hydrophobic effect observed in pure water or highly aqueous mixtures. 

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