ABSTRACT
The chiral C3-symmetric [Mo3S4Cl3(dppe)3]+ cluster [dppe = 1,2-bis(diphenylphosphinoethane), P or M enantiomers] with incomplete cuboidal structure is shown to be configurationally stable at room temperature and configurationally labile at elevated temperature using enantiopure Delta- or Lambda-TRISPHAT [(tris(tetrachlorobenzenediolato)phosphate(V)] anions both as chiral NMR solvating and asymmetry-inducing reagents. It is evidenced that the enantiomers of this trinuclear cluster cation can equilibrate at higher temperature (typically 72 degrees C), and in the presence of the hexacoordinated phosphate anion, a moderate level of stereocontrol (1.2:1) can be achieved. It results in a diastereomeric enrichment of the solution in favor of the heterochiral ion pairs, e.g., M+ Delta- or P+ Lambda-. At higher temperature, a partial racemization of the TRISPHAT anion is also observed, and precipitation at room temperature of [rac-Mo3S4Cl3(dppe)3][rac-TRISPHAT] salts from the diastereomeric enriched solution improves the diastereomeric purity of the mother liquor to a 4:1 ratio. A low-energy pathway for the inverconversion between the [P-Mo3S4Cl3(dppe)3]+ and [M-Mo3S4Cl3(dppe)3]+ enantiomers has been found using combined quantum mechanics and molecular mechanics methodologies. This pathway involves two intermediates with three transition state regions, which result from the partial decoordination of the diphosphane coordinated at each metal center. Such decoordination creates a vacant position on the metal, producing a Lewis acidic site that presumably catalyzes the TRISPHAT epimerization.
ABSTRACT
The addition of enantiopure TRISPHAT anions to chiral cationic cages of type [Co(4)(L)(6)(BF(4))](7+) leads to the enantiodifferentiation of the ligands of the racemic salts and, even more effectively, of the achiral tetrafluoroborate anion trapped inside.
ABSTRACT
The reaction between 8-aminoquinoline, 1,10-phenantholine-2,9-dicarbaldehyde, and copper(I) tetrafluoroborate gave a quantitative yield of a tricopper double helicate. The presence of dynamic covalent imine (C=N) bonds allowed this assembly to participate in two reactions not previously known in helicate chemistry: 1) It could be prepared through subcomponent substitution from a dicopper double helicate that contained aniline residues. An electron-poor aniline was quantitatively displaced; a more electron-rich aniline competed effectively with the aminoquinoline, setting up an equilibrium between dicopper and tricopper helicates that could be displaced towards the tricopper through the addition of further copper(I). 2) Both dicopper and tricopper helicates could be prepared simultaneously from a mixture of phenanthroline dialdehyde, aniline, and aminoquinoline, which contained all possible imine condensation products in equilibrium. Following the addition of copper(I), thermodynamic equilibration on both covalent and coordinative levels eliminated all partially-formed and mixed imine ligands from the mixture, leaving the helicates as exclusive products.
ABSTRACT
Effective homochiral recognition occurs between the cationic [Fe(eilatin)3]2+ complex and TRISPHAT anions even in polar media such as 90% acetone-CHCl3 (de > or = 89%).
ABSTRACT
Chemical reactions and processes often involve chiral, yet racemic, cationic reagents, intermediates or products. To afford instead non racemic 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 towards gaining reliable and predictable control over stereoselective ion pairing phenomena through the synthesis and the use of novel configurationally stable hexacoordinated phosphate anions.
ABSTRACT
A ribose-functionalized bpy ligand has been prepared and shown to give modest diastereomeric excesses of Lambda-[FeL(3)](2+) complexes; interconversion of Delta and Lambda cations is relatively fast, and in CHCl(3), the favored complexes with Delta- or Lambda-TRISPHAT counterions are homochiral, (Delta(+)Delta(-)) or (Lambda(+)Lambda(-)). In the case of the Delta-TRISPHAT salt, a single diastereomer is observed (de > or = 96%).
Subject(s)
Ferrous Compounds/chemistry , Ferrous Compounds/chemical synthesis , Organophosphorus Compounds/chemistry , Ribose , Circular Dichroism , Ligands , Magnetic Resonance Spectroscopy , Molecular Structure , Ribose/analogs & derivatives , Ribose/analysis , Ribose/chemical synthesis , Ribose/chemistry , StereoisomerismABSTRACT
By associating chiral labile [FeL3](2+) complexes with TRISPHAT anions, a stereocontrol of the metal-centered chirality is feasible; the sense of the stereoselective induction and its magnitude strongly depends upon the structure of the diimine ligands (L: bpy, phen).
ABSTRACT
[reaction: see text] beta-Ketoesters can be effectively monofluorinated with F-TEDA using CpTiCl(3) as a catalyst. With the use of this catalyst, the extent of the competing difluorination does not reach 10%. [TiCl(2)(TADDOLato)] complexes catalyze the one-pot enantioselective heterodihalogenation of beta-ketoesters with F-TEDA and NCS to afford alpha-chloro-alpha-fluoro-beta-ketoesters in moderate to good yields. The sequence of addition of the halogenating agents determines the sense of chiral induction.
ABSTRACT
P-Vinylbenzylphosphonic acid (2) was synthesized and crystallized in two phases A and B. The latter phase was easily converted into the former. Both phases were investigated by IR and solid-state (31)P and (1)H NMR spectroscopy, and X-ray crystallography. The use of recently developed NMR methods has enabled us to increase the usually poor resolution of solid-state (1)H spectra. This gave additional insights on the proton environments. In particular, two dimensional 2D (1)H-(31)P heteronuclear correlation (HETCOR) experiments, incorporating a Lee-Golburg homonuclear decoupling scheme, allowed description of the mixture of phase A and B.
