Scandium species

Tml2, and that of other isolated uncommon divalent complexes there are also two endohedral metallofullerenes Sc Cg4 (Takahashi et al., 1995) and Tm C82 (Kirbach and Dunsch, 1996 Pichler et al., 1997) for which spectroscopic evidence points to the divalent nature of Sc and Tm, respectively they are worth mentioning here but they will not be discussed further. We will also consider the important issue of chemical systems in which uncommon divalent species may be present or have been postulated as intermediates, or displaying divalent-like reactivity. We will also report on the few low-valent scandium species that have been reported and finally on the zero-valent compounds. 

Thermochemical properties of scandium species, including Sc (aq), have been evaluated by Travers et al. (1976). For completeness, the properties of scandium species are included in this chapter. Because the ionic radius of Sc " is much smaller than that of any other its properties are not included in inter-series comparisons. 

Based on Mannich-type reactions of N-acryliminoacetates with silyl enol ethers, a new method for the preparation of N-acylated amino acid derivatives via nucleophilic addition to N-acrylimino ester has been developed using a polymer-supported amine and scandium catalysts (Scheme 12.5) [9]. Ethyl N-benzoyl-2-bromoglycine was used as a substrate. It could be readily converted to reactive N-acrylimino ester in situ by treatment with a base. Immobilizations of the amine and the scandium species into polymeric supports prevented loss of activity of the catalyst. The method is simple and provides a convenient method for the preparation of N-acrylated amino acid derivatives. 

There is very good agreement as to both the polymeric species (/ > 1) that form for scandium and to the magnitude of their relative stabilities. Aveston (1966) indicated that no polymeric species containing more than three scandium atoms form, and indeed, no study has identified any polymeric scandium species above a... 

Table 8.6 Literature thermodynamic data for scandium species at 25°C.

Scandium is apparently much more abundant (the 23rd most) in the sun and certain stars than on earth (the 50th most abundant). It is widely distributed on earth, occurring in very minute quantities in over 800 mineral species. The blue color of beryl (aquamarine variety) is said to be due to scandium. It occurs as a principal component in the rare mineral thortveihte, found in Scandinavia and Malagasy. It is also found in the residues remaining after the extrachon of tungsten from Zinnwald wolframite, and in wiikite and bazzite. 

It turned out that the dodecylsulfate surfactants Co(DS)i Ni(DS)2, Cu(DS)2 and Zn(DS)2 containing catalytically active counterions are extremely potent catalysts for the Diels-Alder reaction between 5.1 and 5.2 (see Scheme 5.1). The physical properties of these micelles have been described in the literature and a small number of catalytic studies have been reported. The influence of Cu(DS)2 micelles on the kinetics of quenching of a photoexcited species has been investigated. Interestingly, Kobayashi recently employed surfactants in scandium triflate catalysed aldol reactions". Robinson et al. have demonshuted that the interaction between metal ions and ligand at the surface of dodecylsulfate micelles can be extremely efficient. ... 

Cyclopentadienylamine)scandium(2,3-dimethyl-l,3-butadiene) 7 was synthesized in good yield, as shown in Scheme 2. Complex 7 reacted with benzonitrile to form a /rz-imido complex 8, the structure of which was characterized by single crystal X-ray diffraction. This product 8 was proposed to be formed by nitrile insertion followed by an attack of another diene methylene group on the carbon atom of the imido intermediate.3 An unsaturated metal imido species was formed, which easily dimerized to produce 8. However, the yield of 8 was not reported. 

The thenoyltrifluoroacetate (tta) complex, [Sc tta)3 OP(OBu)3)], has been prepared. Scandium also afforded, with l,2-dihydroxybenzene-3,5-disodium sulphonate (Tiron), a monoprotonated chelate below pH 2.5, but above pH 6.0 hydrolysis afforded a monohydroxo-Sc-Tiron complex. Ligand-exchange equilibria for the piperidium salts of [Y(ffac)4] and [Y(tfac)4] have been studied by n.m.r. spectroscopy. The fully fluorinated ligands appear to exchange faster than the partially fluorinated species, and the mixed compounds, [Y(Hffac) (tfac)4 ] , n = 0 — 4, were obtained. 

Scheme 12.10 Synthesis of scandium methyl surface species by consecutive ligand exchange (cf route C in Scheme 12.3).

The range of transition metal silylamides was also expanded to include the synthesis and structure of the yttrium species [Y N(SiMe3)2 3],2 which, like its previously reported scandium counterpart, has a pyramidal MN3 array. In the vapor phase, the... 

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... 

Up to now, we have considered the interaction of M (Sc, Ti, Ni or Cu) with CO2 to give a MCO2 complex. In the case of scandium and titanium atoms, the interaction with carbon dioxide lead to stable complexes. The point addressed now focusses on the possible insertion of these two atoms in a CO bond of CO 2 to give oxmetal-carbonyl (OMCO) products. Indeed, both functionals indicate the presence of stable OMCO species for Sc and Ti atoms. The results are reported in Figure 6 and Tables 7 and 8. 

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