Scandium halide complexes

Complex halides of scandium and yttrium have been discussed in CCC (1987).1 Most halides and halide complexes reported are of Sc111 and Y111 but there are some reduced halide species such as the diiodide.229... 

The exploration of the chemistry of terphenyl derivatives of the group 3 metals is due mainly to Rabe and coworkers [13-18]. The ligands used were of the formula C6H3-2,6-Ar2 (Ar = CeHs, C6H2-2,4,6-Mc3, 1-naphthyl, or 3-MeO-C6H4). The halide complexes 1-3 could readily be obtained by simple salt metathesis from the reaction of the terphenyl lithium with anhydrous metal trichlorides MCI3 (M = Sc or Y) in THF at room temperature [13,14], The yttilum complexes 2 and 3 were isolated in moderate yield (ca. 50%) however, only a low yield of the scandium complex 1 could be obtained, most likely because of C-H bond activation as indicated by NMR spectroscopy. These metatheses reactions did not proceed in aromatic solvents or hexanes probably as a result of the low solubility of the reactants in these media. Complex 1 decomposes slowly in THF solution, while 2 and 3 are considerably more stable. 

No carbonyl chemistry of scandium and yttrium has been reported yet and there is also no cyanide chemistry of these two elements although thiocyanato complexes of scandium [Sc(NCS)6]3 (bonded through nitrogen) are known. The important developments involving scandium or yttrium with carbon have involved the fullerene derivatives of these elements. There have been some scandium carbide systems prepared but these will be highlighted in the chemistry of the halides. 

A number of pyridines can be alkylated by alkenes with a cationic halfsandwich scandium complex in an enantioselective manner (Scheme 48). The alkylation occurs at C-2 with high yields and high enantiometric excess (ee).The pyridines can be substituted with alkyl, aryls, and halides with no effect of the yields or selectivity. The reaction also occurs on isoquinolines. A number of alkenes will react with 2-picoline with high selectivity and yields (14JA12209). 

Transition metal p-diketiminate complexes are typically prepared by one of three routes. In one, these complexes are prepared by the reaction of a metal halide with an alkali metal P-diketiminate generated from the reaction of the p-diketiminate with an alkali metal base. An example of this synthesis is shown for the scandium system in Equation 4.51 In a second method, these complexes are prepared by the reaction of a transition metal complex containing a basic ligand, such as an alkyl or amido group, with the neutral p-diketimine. Two examples of this route for zirconium systems are shown in Equations 4.52 and 4.53, 3... 

Scandium group elements as well as the lanthanides form allyl complexes in which the central atom has H- 3 oxidation state, while the actinides give compounds possessing + 4 oxidation states (Table 7.14). These complexes are formed by reactions of metal halides with allyl compounds of magnesium, lithium, tin, etc. " " ... 

With the smaller, harder rare earth elements (Gd through Lu), such compounds have never been seen, except for scandium where scandium-defrcient hexagonal perovskites, ASc Xs (A = Rb, Cs X = Cl, Br, I), have been observed. These are discussed together with the perovskite-type halides of R = Sm, Eu, Dy, Tm, Yb below. All other complex hahdes with reduced rare earth metals contain clusters and are discussed in Rare Earth Metal Cluster Complexes. 

Otero A, Lara-Sanchez A, Femandez-Baeza J, et al. New achiral and chiral NNE heteroscorpionate ligands. Synthesis of homoleptic lithium complexes as well as halide and alkyl scandium and yttrium complexes. Dalton Trans. 2010 39 930-940. 

The actual situation that exists in solutions of rare earth salts in either aqueous or non-aqueous solution is complicated by concentration effects that can lead to both inner and outer sphere anion coordination as well as to the possibility of hydroxo-containing species particularly in the case of scandium. Inner sphere complexes containing halide ions, nitrate ions, sulfate ions (Choppin, 1971) and even the perchlorate ion (Fratiello et al., 1973 Silber, 1974) have been identified. Consequently, the interpretation of results obtained from measurements of conductance, density, partial molal volume, reaction kinetics, formation constants, and solution spectra can be extraordinarily complicated. 

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