Scandium isopropoxides

Varela et al. [40] obtained similar results from 2,3,4,5-tetra-O-methyl-D-galac-tono-1,6-lactone (20). The homopolymerization of this lactone, promoted by aluminum isopropoxide [Al(0 Pr)3] or scandium triflate [Sc(OTf)3], was attempted. 

Treatment of scandium, yttrium and the lanthanides with refluxing isopropyl alcohol in the presence of HgCl2 (10—3—10 4 equivalents) leads to the metal isopropoxide, which can then be crystallized from the excess isopropyl alcohol (equation 3).17,18... 

The formation of multiple metal-oxo bonds by penta or hexa valent transition metals (d°) is not surprising but the more recent discovery that scandium, yttrium, and the tervalent lanthanides form oxo-isopropoxides rather than triisopropoxides was unexpected. Considerable efforts have been devoted to ensuring that the formation of these pentanuclear oxo-alkoxides [M5(/r5-0)(/r,3-0Pr )4(/r-0Pr )4(0Pr )5] was not due to hydrolysis, and there is evidence that elimination of ether is involved. An alternative mode of decomposition would be alkene elimination with concomitant formation of alcohol (Eq. 5.5). 

The spectrum of scandium alumoisopropoxide displays 3 doublets with the relative intensity 1 1 3. The identity of this spectrum with the spectrum of tetrameric aluminium isopropoxide confirms the shown above structure of similar associates. The structure with the central 6-coordinated REM atom is supposed for zirconoalkoxides as well [54]. The Li and Na derivatives obviously have an analogous structure, however, the coordinating number of the REM atom in these complexes decreases to 4. 

Calixarene complexes with lanthanides have been developed to catalyze the homopolymerization of TMC and DTC. The complexes were synthesized from lanthanide isopropoxide and appropriate p-tcrt-butylcalix[n]arene (n = 4, 6, and 8). Based on the polar solvent effect, the end-group examination of the polymers, and NMR analyses of the growing chain, it could be concluded that the polymerizations of TMC and DTC initiated by p-tcrt-butylcalix[n]arene (n = 4, 6, and 8) complexes of Nd, La, and Y proceeded by a coordination-insertion mechanism. Cou et used scandium p-tcrt-... 

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