Tris , cryptand metal complexation

Macrobicyclic cascade cryptands have also been prepared such as the series of bis(tren) derived (tren = tris(2-aminoethyl) amine, see Section 4.4.3) compounds 5.9. The di-nickel(II) and di-copper(II) complexes of the cages with various spacers all bind a metal cation into each tren unit. These metal... 

Neutral Ti(CO)6 is an extremely unstable compound which decomposed even below -220 °C, as shown by matrix isolation spectroscopy [165]. The much more stable phosphine derivatives Ti(CO)3(dmpe)2, Ti(CO)5(dmpe), Ti(CO)5(PMe3)2, Ti(CO)4(PMe3)3 have been isolated [166-168]. In contrast, the dianionic salt [Ti(CO)6] (53) is thermally much more stable and decomposes only above 200 C. Complex 53 was obtained by reductive carbonylation of Ti(CO)3(dmpe)2 by alkali metal naphthalenides in the presence of cryptand [169]. Carbonylation of 79 also produces 53 [170]. The naph-thalenide-assisted reductive carbonylation of the zirconium tetrachloride afforded the zirconium analog [Zr(CO)6] (54) [171], which was also derived by carbonylation of the tris(diene) dianion 45 [150]. One anion [R3Sn] effectively stabilizes Ti(CO)e as an air stable monoanionic salt, [R3SnTi(CO)J [172]. 

Transition metal cations can be made organically soluble by complexation with a crown ether, a polyethylene glycol) or its dimethyl ether (an open crown) or tris(3,6-dioxaheptyl)amine (TDA-1, an open cryptand, 1). TDA-1 is very hydrophilic and is most useful for the solubilization of solid salts. On the other hand, it also forms complexes with some metal carbonyls. Alternatively, a very lipophilic anion (for instance stearate) can make a salt organic. Finally, some other special ligand (e.g., a bipyridine-N,N -dioxide derivative) can be used. In all these cases positively charged species are brought into the organic phase for reaction. 

Since the concept of endohedral fullerenes is important in the context of the current presentation, the CPK structure of C50 is presented in figure 1 next to the structure of a cryptate, in this case the lanthanum complex of tris-bipyridyl cryptand, [La(bipy)3]. For the sake of the argument being presented here, assume that the 60 is really an endohedral complex of some metallic ion or ions. 

The species that results from the reductive electrocrystallization of the sodium complex of tris-bipy cryptate, the schematic structure of which is shown in figure 2, has been called a "cryptatium." The name was chosen to express the dual nature of its procedence, since it is part cryptate and part sodium metal. It must be stressed that this cryptatium material is electroneutral, thus forming an expanded atom structure. Figure 2 also shows the schematic structure of an electride and that of a simple sodium atom, to illustrate two additional and extreme situations. In one, the electride, the complexation of the metal ion by the cryptand is so strong that the electron is essentially expelled from its interaction with the cationic center. In the other, the simple sodium atom, the outermost electron resides in an s orbital of the metallic center. Cryptatium thus represents an in-between situation, where the electron is not totally expelled from its interaction with the cation but it does not reside on the cation either, but rather on the ligand. The result is an expanded-metal type structure, where the electron is localized in the ligand structure. 

A study of the synthesis and properties of the tris-cyclohexyl cryptand (76) has been reported in an effort to determine whether the greater enforced separation of any included metal cation from its counter-anion would influence the PT catalysis activity. The results are not clear-cut, owing presumably to the intervention of other factors, but seem to show increased anion nucleophilicity at least in the case of complexed KI. 

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