Scandium complexes 3-diketonates

It is a commonplace to say that there has been explosive growth in the use of lanthanides in organic chemistry. For many years, the use of cerium(iv) compounds as oxidants was widespread, but more recently a whole range of other compounds have made their appearance. Thus samarium(ii) compounds are now routinely used as one-electron reducing agents and the use of trifluoromethanesulfonate ( triflate ) salts of scandium and the lanthanides as water-soluble Lewis acid catalysts is widespread. Beta-diketonate complexes and alkoxides have also come into use there are even applications of mischmetal in organic synthesis. 

Many of the early reports of complexes with bidentate oxygen ligands involved acac complexes and the /3-diketonate and related ligands were discussed in CCC (1987).210 The /3-diketonate complexes of scandium and yttrium and the lanthanides were also discussed in CCC (1987).1 Many reported systems contained adducts formed by the metal /3-diketonate complexes. In solution some of the complexes with bidentate ligands can expand their coordination number to seven by coordination to a suitable donor ligand. A solvent extraction method has been used to show that Sc(acac)3 does not form an adduct with trioctylphosphine oxide but tris(tropolonato)scandium(III) and tris-(ethylmatolato)scandium(III) do coordinate with trioctylphosphine oxide.211... 

The j8-diketones are excellent chelating ligands for the rare earth ions and typical examples of the types of complexes that are formed are presented in table 25.14. (The functioning of these complexes as lasers is discussed in ch. 35.) The complexes that might have been expected, R(jS-diketone)3, rarely form, except for scandium, because of the tendencies of these compounds to add one or more additional ligands, particularly water molecules. Attempts to dehydrate most of these hydrated species leads either to destruction of the complex or the formation of polymeric hydroxo species (Pope et al., 1961). If, however, the substituents on the j8-diketone are large, t-butyl groups as an example, then the anhydrous tris chelate can be prepared (eisentraut and Sievers, 1965). The anhydrous trisacetylacetonato complexes have been prepared, however, in the absence of any possible adduct formation by the reaction of acetylacetone directly with a rare earth hydride (Przystal et al., 1971). The anhydrous acetyl-... 

Sc(acac)3] crystallizes in the orthorhombic space group Pbca (Andersen et al., 1973). The stmcture consists of discrete Sc(acac)3 molecules. The scandium(III) ion is six-coordinate, and the coordination polyhedron can be described as a slightly distorted octahedron (fig. 7). The site symmetry is close to D3. Another example of a six-coordinate scandium(III) )3-diketonate complex is [Sc(dbm)3] (Zaitseva et al., 1990). Two different crystal structures are described, one with a triclinic and one with a monochnic cell. So far, no scandium(lll) )3-diketonates with coordination number higher than six have been described. Because of the small ion size of Sc +, coordination number six is the general rule fortius rare-earth ion. Also in the trinuclear scandium(III) disiloxanediolate complex [(Ph2Si0)20]2Sc3(acac)5], the coordination number of Sc + is six as well (Lorenz et al., 2001) (fig. 8). 

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