Trisphat Anions

TRISPHAT anion 8 seems to be more particularly efficient with cationic metallo-organic and organometallic substrates. BINPHAT 15 has often-supe-rior chiral shift properties than 8 when associated with organic cations such as ammonium cation 68 (Fig. 24). In all these examples, solvent polarity influences the quality of the separation since ion association is crucial. Solvent or solvent mixtures of low polarity are preferred for these experiments. 

Preparative chromatographic resolution procedures have overall freed chemists from the constraint of dependency on crystallization. They are most often performed with covalent diastereomer mixtures but ionic salts can also be separated. Recently, it was found that the lipophilicity of TRISPHAT anion 8 profoundly modifies the chromatographic properties of the cations associated with it and the resulting ion pairs are usually poorly retained on polar chromatographic phases (Si02, AI2O3) [131]. Using enantiopure TRISPHAT anion. 

The lipophilicity of the TRISPHAT anion 8 also confers to its salts an affinity for organic solvents and, once dissolved, the ion pairs do not partition in aqueous layers. This rather uncommon property was used by Lacour s group to develop a simple and practical resolution procedure of chiral cationic coordination complexes by asymmetric extraction [134,135]. Selectivity ratios as high as 35 1 were measured for the enantiomers of ruthenium(II) trisdiimine complexes, demonstrating without ambiguity the efficiency of the resolution procedure [134]. 

There are very few examples of asymmetric synthesis using optically pure ions as chiral-inducing agents for the control of the configuration at the metal center. Chiral anions for such an apphcation have recently been reviewed by Lacour [19]. For example, the chiral enantiomerically pure Trisphat anion was successfully used for the stereoselective synthesis of tris-diimine-Fe(ll) complex, made configurationally stable because of the presence of a tetradentate bis(l,10-phenanthroline) ligand (Fig. 9) [29]. Excellent diastereoselectivity (>20 1) was demonstrated as a consequence of the preferred homochiral association of the anion and the iron(ll) complex and evidence for a thermodynamic control of the selectivity was obtained. The two diastereoisomers can be efficiently separated by ion-pair chromatography on silica gel plates with excellent yields. 

The Z)3-symmetric TRISPHAT anion 88, tris(tetrachlorobenzenediolato)phosphate, is chiral and configurationally stable. It can be resolved by association with chiral ammonium salts such as cinchonidine <1997AGE608, 2004JOC8521>. TRISPHAT 88 displays high selectivity for cinchonidine and does not associate with the related diasteromer cinchonine <1998TL4825>. The selective ion pairing behavior of TRISPHAT has been exploited in... 

Lacour et al. have shown that the ion pairing of Bulman Page s iminium cation 66 with a tris(tetrachlorobenzenediolato)phosphate(v) (TRISPHAT) anion allows the use of strict biphasic conditions leading to higher enantioselectivities when compared to a tetraphenylborate counterion (Scheme 26) <2002TL8257>. 

View of the Cinchonidinium cation (left) and of the Trisphat anion (right). 

In the past decade many groups from aU over the world were interested in the use of the A-TRISPHAT anion to differentiate chiral racemic compounds by H-and... 

The structure of 4.18a shows that the two Cp Ru units are bonded to the carbazolyl ligand and are disposed in a trans fashion. Most remarkable is the interaction between the TRISPHAT anion and the cationic metal complex. There are two n-n interactions between one of the tetrachloro-benzene rings of A-TRISPHAT and the two t/ -Cp Ru units of two cationic metal complexes with (J = 3.55 (1) A a = 19.24°) for the C(13)-C... 

A-TRISPHAT anion intercalates between two cationic complexes providing a onedimensional supramolecular chain. To our knowledge this example represented the first direct observation of chiral recognition between the A-TRISPHAT and any chiral organometallic species at least in the solid state. We also feel that this resolution originates from supramolecular control. 

Compounds with 6-coordinated P atoms can be obtained from some diphosphetes (6.905) and salts of the trisphosphat (or trisphat ) anion (6.906) and other large rings have been well characterised [80-82]. 

The trisphat anion (6.906) has the ability to discriminate between chiral cations and this anion has turned out to be a valuable chiral, solvating, resolving, asymmetry-inducing and solubilising reagent. 

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