Alkali metal complexes solvates

However, the earliest method leading to the isolation of organosilyl derivatives of Zn, Cd and Hg makes use of liq NHj as solvent for the formation of R3Si-alkali-metal complexes. For example, when hexaphenyldisilane is treated with potassium in liq NH3 a red-brown solution of solvated KSiPhj is formed and, on addition of anhyd ZnClj, the color is discharged in an exothermic reaction ... 

Oxygen chelates such as those of edta and polyphosphates are of importance in analytical chemistry and in removing Ca ions from hard water. There is no unique. sequence of stabilities since these depend sensitively on a variety of factors where geometrical considerations are not important the smaller ions tend to form the stronger complexes but in polydentate macrocycles steric factors can be crucial. Thus dicyclohexyl-18-crown-6 (p. 96) forms much stronger complexes with Sr and Ba than with Ca (or the alkali metals) as shown in Fig. 5.6. Structural data are also available and an example of a solvated 8-coordinate Ca complex [(benzo-l5-crown-5)-Ca(NCS)2-MeOH] is shown in Fig. 5.7. The coordination polyhedron is not regular Ca lies above the mean plane of the 5 ether oxygens... 

The study of solvated alkali metal allyl species remains a complex topic due to a variety of reorganization processes. Structural data on alkali metal allyl derivatives include [G3H5Li(TMEDA)] 133,139 where solvated lithium ions act as... 

Far fewer structural studies have been conducted for the alkali metal chalcogenolates Se-M and Te-M. Nevertheless, the general aggregation patterns emerging are similar to those for S-M complexes, with solvated monomers and ring dimers being the dominant aggregation states for the reported structures.404... 

The importance of alkali metal binding with available 7r-electron density in the formation of CIPs was also demonstrated by Niemeyer in the structural elucidation of the first monomeric non-solvated lithium cuprate, [(2,6-Mcs2(LI L)2CuLi] 450, formed from the reaction of 2 equiv. of (2,6-Mcs2Gf,I L)Li with /-BuOCu in pentane.447 The complex crystallizes as two different independent molecules in which the C-Cu-C angles differ (171.1° and 173.8°) as does the mode of coordination to the Li cations C pso and rf to one pendant Ph in molecule 1, with an additional rf interaction to a second Ph group in molecule 2. In the second molecule, the Li site is 10% occupied by a Cu ion. 

Sulfur diimides react quantitatively with organolithium reagents at the sulfur centre to produce lithium sulfinimidinates of the type Li[RS(NR )2] A. The lithium derivatives may be hydrolysed by water to R NS(R)NHR which, upon treatment with MH (M=Na, K) or the metal (M=Rb, Cs) in THF, produces the heavier alkali-metal derivatives.132 The structures of these complexes are influenced by (a) the size and electronic properties of the R group, (b) the size of the alkali metal cation, and (c) solvation of the alkali-metal cation. 

To date only one polyanionic arsenide complex of an alkali metal has been reported. The complex [B GejAslSiPrilLijsh is obtained from the reaction of Bu GeF3 with 3 equiv of Li AsH(SiPii) and BuLi in ether in 24% yield (107). The complex contains a Ge2As6Li6 framework with a center of symmetry in a distorted rhombododecahedral arrangement (Fig. 13). Each As atom is thus bound to three Li atoms in addition to one Ge atom and one exocyclic SiPr( group the Li atoms are in contact with three As atoms and also with two H atoms from different SiPr], groups [Li-As = 2.52(2) to 2.62(2) A], Additional solvation of the Li atoms is not observed, even though the complex is syn-... 

Lariat ethers of structure 8 were found to be selective toward Li ion and the lariat crown ether-Li+ complexes are more stable than the corresponding complexes with Na or K+, in methanol. Nevertheless, experiments conducted in aqueous solution showed that Na+ had a better complexation ability than the other two alkali metal cations. Hence, selective complexation of lariat crown ethers with cations changes with the solvent system this may be due in part to the difference in solvation between solvent and cation (Figure 9 f. ... 

The solvents used in these rhodium-catalyzed reactions may also act as complexing agents for counterions of the anionic rhodium complexes. For example, tetraglyme is known to coordinate alkali metal cations. Such solvation decreases the possibility of the cation interacting with the anionic rhodium catalyst and lowering its activity or solubility. The crown ethers, such as [18]-crown-6... 

Fluorinations by alkali metal fluorides are often carried out in high-boiling solvents. Crown ethers have been used to solvate inorganic fluorides by complexation. 

Dioxane and Water. Grunwald and co-workers (GBK) (7) used a vapor pressure method to obtain the differential of the free energy of transfer of a solute with respect to solvent mole fraction at 50 wt% dioxane. On the basis of what has now become known as the large-ion assumption (8), they separated cation and anion effects by equating the free energies of transfer for tetraphenylborate and tetraphenylphosphonium ions. They concluded that Na+ was preferentially solvated by dioxane, a surprising result then, but less unexpected now that complexes of the alkali metals with polyethers have been discovered (dioxane... 

---