Hexacoordinated phosphates: how to teach old chiral anions new asymmetric tricks

Abstract

Chemical reactions and processes often involve chiral, yet racemic, cationic reagents, intermediates, or products. To afford instead nonracemic or enantiopure compounds, an asymmetric ion pairing of the cations with enantiopure anions can be considered—the counter ions behaving as asymmetric auxiliaries, ligands, or reagents. Detailed herein is a short review of our approach toward gaining reliable and predictable control over stereoselective ion pairing phenomena through the synthesis and use of novel configurationally stable hexacoordinated phosphate anions. © 2007 The Japan Chemical Journal Forum and Wiley Periodicals, Inc. Chem Rec 7: 275–285; 2007: Published online in Wiley InterScience (http://www.interscience.wiley.com) DOI 10.1002/tcr.20124

Resolution of the First Nonracemic Diquats

“…[13] Hexacoordinated phosphates BINPHAT 2 [14] and TRISPHAT 3 [15] ( Figure 2) were considered to be the best choice in that respect. [16,17] Supramolecular stereocontrol over the configuration of the bipyridinium cations was achieved by the chiral anions acting as noncovalent chiral auxiliaries. A moderate but definite diastereoselectivity was obAbstract: Three tricyclic diquats with an eight-membered ring were prepared and shown to be the first configurationally stable derivatives of their kind.…”

“…They are, in addition, effective NMR chiral-solvating and asymmetry-inducing reagents. [17] Anion pairing of cations 4 a, 4 b, and 4 c with anions 2 and 3 was, therefore, studied.…”

Asymmetric Synthesis of Stereogenic Phosphorus P(V) Centers Using Chiral Nucleophilic Catalysis

“…These compounds normally have stable configurations depending on the nature of the substitution around the phosphorus center [9]. Chiral phosphate mimics have been extensively utilized in transition metal catalysts, [10] as chiral reagents, [11][12][13] and in coordination chemistry [14,15]. Furthermore, compounds with stereogenic phosphonate centers are of great interest in biological applications [16].…”

NMR enantiodifferentiation of quaternary ammonium salts of Tröger base

“…14 This diamagnetic chiral anion is an effective NMR chiral solvating agent (CSA) for cationic metalloorganic and organometallic substances. [15][16][17][18] With organic cations, [19][20][21][22][23][24][25][26] anion 1 leads often to superior NMR enantiodifferentiations than related TRIS-PHAT 2 (tris(tetrachlorobenzenediolato) phosphate(v), Fig. 1).…”