Scandium derivatives

By treating Nafion (NR-50), a perfluorinated acidic ion exchanger based on sulfonic acid groups, with scandium(III) chloride hexahydrate Kobayashi et al. generated a solid scandium-derived catalyst (29) (Nafion-Sc) that proved to be effective in al-lylation reactions of carbonyl compounds with tetraallyltin (Scheme 4.15). Since the catalyst is stable in both organic solvents and water, even unprotected carbohydrates could be transformed directly in aqueous solvents. The resulting homo-allylic alcohols were separated by simple filtration [97]. 

Heterobimetallic binol catalyst based on titanium, aluminum, and scandium have also been reported.40 The results showed that the titanium catalyst was not effective. While the aluminum catalyst was better, it turned out that the scandium derivative was the most efficient. 

The relative rates found for /1-H and /1-alkyl elimination are very variable and dependent on the specific complex. Faster /1-alkyl elimination by a factor of 10 was found for the manifold decomposition of [Lu(Cp )2(CH2CH(CH3)2] (Scheme 6.46) [142]. However the rate of /1-H elimination is higher in the decomposition of a related scandium derivative (Scheme 6.47) [143]. 

The scandium derivative has been prepared from ScClj and magnesium cyclo- ... 

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 ... 

An analogous scandium derivative was prepared from dicyclopentadienyl scandium chloride and Li(CH2)2PPh2 in ether. It was characterized by proton NMR SCp 6.0 ppm and 6CH2 0.86 ppm as a doublet with V(HP)=11 Hz (Manzer, 1976). 

The analogous scandium derivatives have been intensively studied recently (58), as well as the corresponding yttrium compounds (89). 

It is noteworthy that the two structures of the scandium derivatives, SC2X3, are both related to close packed structures of the general MX types, in which vacancies appear on the metal sites. It is a consequence of the affinity of scandium (also Yb(III) and Lu) for regular octahedral sites. This behavior is observed in the lower chalcogenides as well. 

In the case of the scandium derivatives, this element is on the octahedral sites, and a large number of R elements accept the VIII prismatic coordination (from La to Er) (Rodier et al., 1969). 

The guanidinate-supported titanium imido complex [Me2NC(NPr02l2Ti = NAr (Ar = 2,6-Me2C6H3) (cf. Section IILB.2) was reported to be an effective catalyst for the hydroamination of alkynes. The catalytic activity of bulky amidinato bis(alkyl) complexes of scandium and yttrium (cf. Section III.B.l) in the intramolecular hydroamination/cyclization of 2,2-dimethyl-4-pentenylamine has been investigated and compared to the activity of the corresponding cationic mono(alkyl) derivatives. 

Scott Oakes et al. (1999a, b) have shown how adoption of SC conditions can lead to a dramatic pressure-dependent enhancement of diastereoselectivity. In the case of sulphoxidation of cysteine derivatives with rert-butyl hydroperoxide, with cationic ion-exchange resin Amberlyst-15 as a catalyst, 95% de was realized at 40 °C and with SC CO2. By contrast, with conventional solvents no distereoselectivity was observed. Another example is the Diels-Alder reaction of acrylates with cyclopentadiene in SC CO2 at 50 °C, with scandium tris (trifluoromethanesulphonate) as a Lewis acid catalyst. The endoiexo ratio of the product was as high as 24 1, while in a solvent like toluene it was only 10 1. 

The enthalpies of solution and solubilities reviewed here provide much of the experimental information required in the derivation of single-ion hydration and solvation enthalpies, Gibbs free energies, and entropies for scandium, yttrium, and lanthanide 3+ cations. 

Nitrosalicylhydrazide, 2778 Scandium 3-nitrobenzoate, 3816 Silver osmate, 0034 Thallium bromate, 0260 Thallium(I) methanediazoate, 0458 Thallium(I) 2- or 4-nitrophenoxide, 2187 Thallium acz-phenylnitromethanide, 2723 See also METAL AZIDES, METAL CYANIDES (AND CYANO COMPLEXES), /V-MKTAL DERIVATIVES... 

Scandium - the atomic number is 21 and the chemical symbol is Sc. The name derives from the Latin scandia for Scandinavia , where the mineral were found. It was discovered by the Swedish chemist Lars-Fredrik Nilson in 1879 from an ytterbium sample. In the same year, the Swedish chemist Per Theodore Cleve proved that scandium was Mendeleev s hypothetical element eka-boron , whose properties and position in the Period Table Mendeleev had previously predicted. 

Analogous methyl compoimds are iU-characterized and appear to be polymeric [129). The air-sensitive phenyl derivatives when first obtained from THF are soluble in benzene, but when dried completely are no longer soluble — apparently due to pol5unerization. The homoaryl complexes of the smaller scandium, and yttrium ions form only the tris complexes Sc(CeH5)3 and Y(C6H5)3 [129) It is apparent that the structure and stabihty of the homoaryls are dependent on the metal ionic radii and the steric bulkiness of the phenyl group. 

Interestingly, the use of Sc(OTf)3 as the promoter gave hydroxyalkyl-6,7-dihydrobenzofuran-4(57/)-one derivatives 17 from D-ribose (9), whereas scandium cation-exchanged montmorillonite (Sc -mont) afforded hydroxyalkyl-3,3,6,6,-tetramethyl-3,4,5,6,7,9-hexahydro-l//-xanthene-l,8(27/)-dione (18) in good yield [97] (Scheme 3). 

The enantioselective addition of ally organometallics to carbonyls has become one of the workhorses of organic synthesis. Dennis Hall of the University of Alberta reports (J. Am. Chem. Soc. 125 10160, 2003) the scandium triflate catalysis chiral allylboronic acids become more effective tools. The best of these, the Hoffmann camphor derivative 2, adds to aldehydes under Sc(OTf), catalysis with excellent enantiomeric excess. The reaction works equally well for methallyl, and for the E and Z crotyl boronic acids. The crotyl derivatives react with the expected high diastereocontrol. A limitation to the boronate additions is that branched chain aldehydes give low yields. 

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