Complexation with alkylammonium salts

Also of importance for analytical and structural studies are the complexes with alkylammonium salts, widely used under selective conditions of critical electrolyte concentrations (see Section III). 

In the preceding section it was shown that the stability of crown-ether complexes with alkylammonium salts depends on the relationship between the structures of the crown ethers and the ammonium ions. How critically this relationship determines the complex stability will become clear in this section, which deals with the discrimination between the two enantiomers of racemic salts by chiral macrocyclic ligands. 

Menozzi E, Rebek Jr J. Metal directed assembly of ditopic containers and their complexes with alkylammonium salts. Chem Comm. 2005 5530—5532. 

BF3 reacts smoothly, in inert solvents, with alkali metal sulfates and phosphates to give stable 2 1 and 3 1 complexes (Table 9), whereas the intermediate complexes that form with NOT, SO and COl- decompose to [BF4] and B203.55 Brownstein et al. have established114 that BF3 reacts easily with alkylammonium salts in CH2C12 or liquid S02. [BF3A]- complex anions are formed with the salts of strong acids (equation 17) whereas complexes with salts of weak acids easily undergo disproportionation (equation 18) and/or conversion into a 2 1... 

A unique method for selective acylation of secondary amines in the presence of primary amines involves the use of 18-Crown-6 with acetic anhydride and triethylamine. It is believed that the 18-crown-6 complexes primary alkylammonium salts more tightly than the secondary salts, allowing selective acetylation. 

Iron hahdes react with haHde salts to afford anionic haHde complexes. Because kon(III) is a hard acid, the complexes that it forms are most stable with F and decrease ki both coordination number and stabiHty with heavier haHdes. No stable F complexes are known. [FeF (H20)] is the predominant kon fluoride species ki aqueous solution. The [FeF ] ion can be prepared ki fused salts. Whereas six-coordinate [FeCy is known, four-coordinate complexes are favored for chloride. Salts of tetrahedral [FeCfy] can be isolated if large cations such as tetraphenfyarsonium or tetra alkylammonium are used. [FeBrJ is known but is thermally unstable and disproportionates to kon(II) and bromine. Complex anions of kon(II) hahdes are less common. [FeCfy] has been obtained from FeCfy by reaction with alkaH metal chlorides ki the melt or with tetraethyl ammonium chloride ki deoxygenated ethanol. 

In a similar manner, the diffusion of hexane into dichloromethane solutions containing mixtures of the alkylammonium salts of bromide and the olefinic acceptors o-CA and TCNE result in the formation of brown-red crystals [23]. X-ray analysis reveals the (1 1) complex of bromide with o-CA, in which the anion is located over the center of the C - C bond of the acceptor moiety (Fig. 15b) and Br - C contacts are shortened by as much as 0.6 A relative to the sum of van der Waals radii (Table 3). In bromide complexes with TCNE, the location of the anion relative to the acceptor is variable. In fact, a 2 1 complex [(Br )2,TCNE] is isolated in which both anions reside over the olefinic bond when the tetraethylammonium salt of bromide is used. In comparison, if the tetrapropyl- or tetrabutylammonium salts of the same anion are employed, the (1 1) complexes [Br ,TCNE] are formed in which the bromide donors are shifted toward the cyano substituents (Fig. 15a). In both cases however, the short intermolecular separations that are characteris-... 

Certain long-chain alkylammonium salts, notably tricaprylmethyl-ammonium chloride (Aliquat 336-S) and tri-Ao-octylamine hydrochloride (TIOA) are liquids, sometimes referred to as liquid anion exchangers, which can form extractable ion pairs or aggregates with anionic metal complexes in the... 

Hydrogen peroxide may be efficiently employed for the epoxidation of unfunctionalized aikenes in the presence of polyoxo complexes of tungsten and molybdenum . Venturello and coworkers first developed a phosphotungstate catalyst , with particular emphasis on the tetrakis(diperoxotungsto)phosphate anion P04[W(0)(02)2]4 , 37 , that in conjunction with H2O2 and a lipophilic tetra-alkylammonium salt Q+X as phase transfer... 

The ability of crown polyethers to form complexes with ammonium and alkylammonium salts") gave rise to the development of Cram s concept of host-guest chemistry57). Asymmetric macrocyclic polyethers (host molecules) were designed and synthesized that distinguish between the enantiomers of chiral amine salts (guest molecules). For example, the (R,Reform of polyether (Fig. 66) which was obtained in pure state, forms complexes of different... 

Compound (4) reacts with halides, preferably their alkylammonium salts, in acetone or DME with exchange of one CO for a halide, giving anionic complexes of the type Co(CO)2(NO)X (X = Cl, Br, I, CN) (equation 29). Owing to the high charge density at the metal, these anions can act as sources for the hyponitrous ion, NO, which is transferred in nucleophilic substitutions at activated (benzyl) halides, giving aldoximes (e.g. PhCH=NOH from PhCH2Y) (equation 30). ... 

Non-aqueous solutions of the XWuM complexes may be prepared from tetra-alkylammonium salts or by using phase transfer agents. The coordination of the organic solvent to M, replacing the water molecule, usually takes place with donor solvents. Dehydration of some (but not all) of the XWnM(H20) anions occurs after phase transfer for solvents like toluene with formation of species with a free... 

Complexation experiments by Mock et al. [44, 45, 46] proved that Cucurbituril (53) forms 1 1 complexes with a number of alkylammonium salts where the guest is situated in the cavity of the host. The most stable host-guest complexes are observed with alkyldiammonium salts the dissociation constants are remarkably high to 10 moll . Binding results mainly from ion-dipole interactions... 

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