Complexes scandium

The other direction concerns the use of immobilized transition metal catalysts in the synthesis of libraries of organic compounds of interest in therapeutic drug discovery. One such strategy uses immobilized catalysts (e.g., scandium complexes), leading to efficient library syntheses of quinolines, amino ketones, and amino acid esters.72,73... 

A scandium complex, Cp ScH, also polymerizes ethylene, but does not polymerize propylene and isobutene [125]. On the other hand, a linked amidocyclo-pentadienyl complex [ Me2Si( / 5-C5 Me4)( /1 -NCMe3) Sc(H)(PMe3)] 2 slowly polymerizes propylene, 1-butene, and 1-pentene to yield atactic polymers with low molecular weight (Mn = 3000-7000) [126, 115]. A chiral, C2-symmetric ansa-metallocene complex of yttrium, [rac-Me2Si(C5H2SiMe3-2-Buf-4)2YH]2, polymerizes propylene, 1-butene, 1-pentene, and 1-hexene slowly over a period of several days at 25°C to afford isotactic polymers with modest molecular weight [114]. 

In the very recent past, metal complex catalysis has been used with advantage for the stereo- and enantio selective syntheses based on the Henry and Michael reactions with SENAs (454-458). The characteristic features of these transformations can be exemplified by catalysis of the reactions of SENAs (327) with functionalized imides (328) by ligated trivalent scandium complexes or mono-and divalent copper complexes (454) (Scheme 3.192). Apparently, the catalyst initially forms a complex with imide (328), which reacts with nitronate (327) to give the key intermediate A. Evidently, diastereo- and enantioselectivity of the process are associated with preferable transformations of this intermediate. 

Two other dimeric complexes which are related in structure to [Yb-(C5H4(CH3))2C1]2 are [Ce(C8H8)Cl 2THF]2 and [Sc(C5H5)2Cl]a. The cerium complex was discussed earlier. The structure of the scandium complex 118) is the same as that in Fig. 11. For the planar unit with symmetrical bridges, changing... 

Scandium complexes readily with 8-hydroxyquinolinate ion. Many years ago, Sc(hq)3-Hhq, which was obtained from aqueous solution, was described,97 and this compound does not lose Hhq cleanly on heating but does so in benzene solution.98 However, it has been stated that the solid deposited at about pH 7 is in fact Sc(hq)3." More recently, stability constant values have been determined for the Sc3+/hq-/50% aqueous dioxane system and the corresponding 2-methyl-8-hydroxyquinoline system.100 Chinese workers, who are showing some interest in spectrophotometric analysis, have detected Sc3+ on the microgram scale by fluorometry using -5-sulfonate and cetyltrimethylammonium bromide as an extractant... 

Scandium complexes with chloride ion in aqueous solution, and there is ion-exchange evidence for anionic species, presumably ScClJ aq, in concentrated hydrochloric acid,119 while values of K = 90 and K2 - 37 for the first two association constants have been reported.1211 Solid salts of the anions ScClt-, St Cll- and ScCl2- have been isolated with alkali metal cations.121,122 It seems likely that both the first two species are octahedral and bridged-octahedral respectively, in line with Cs2NaScCl6 which has an X-ray powder pattern in accord with a face-centred cubic structure.123... 

Reaction of Cp LuH with pyridine yielded the orthometallated (C,N->/2) pyridine complexes under release of hydrogen [205]. The scandium complexes CpfScR (R = H, CH3, C6H5, CH2C6H5) show a similar reaction [206]. 

Addition of Sc-R moieties to metal coordinated carbon monoxide was ascribed to the high Lewis acidity of the organometallic scandium complexes [281b]. R-Substituted scandoxycarbene complexes of type Cp2M=C(R)OScCpf (M = Mo, W R = H, Me) and CpM(CO)[=C(R)OScCpf] (M = Co,Rh, R = H, Me, CH2CH2Ph, NMe2) were obtained. The molecular structure of... 

In the instance of scandium, where dissolution is complete in 12 hours, the complex is converted to its dimethylformamide (DMF) adduct,8 Sc(fod)s-DMF, by heating the reaction product in excess DMF. Three recrystallizations of the crude adduct from DMF at 10°C. yield a pure DMF adduct. The scandium complex, Sc (fod), is regenerated from the adduct by heating at 60°C. in vacuo for 12 hours. 

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... 

Lanthanide triflates catalyse Diels-Alder reactions, with the scandium complex as the most effective catalyst, and, again, the catalyst can be recovered and reused, being just as effective in subsequent runs. 

When a chiral scandium complex of 2,6-bis-(oxazolinyl)pyridine, [Sc(/f)-py-box](OTf)3, 0Tf=0S02CE3, is employed instead of Sc(OTf)3, a 2 2 chiral Jt-dimer complex of 1,4-napthosemquinone radical anion (NQ ) with Sc (R)-... 

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