Richard Frantz

New chiral anion mediated asymmetric chemistry

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.

Conformationally-locked metallomacrocycles—prototypes for a novel type of axial chirality

A series of ditopic ligands incorporating two 2,2′:6′,2″-terpyridine (tpy) metal-binding domains linked to a central naphthalenediyl core by ethyleneoxy chains of various lengths have been prepared and their iron(II) complexes prepared. The major thermodynamic products of complexation are ferracycles of [1 + 1], [2 + 2] or [3 + 3] stoichiometry. In the case of the [1 + 1] complexes, the linker between the two tpy domains is spatially restricted and the cations exhibit chirality associated with the conformation about the central N–Fe–N bonds. The dynamic processes by which the enantiomeric forms interconvert are investigated in the presence of chiral anions by NMR and circular dichroism spectroscopy making use of the Pfeiffer effect. We have shown that ditopic bis(2,2′:6′,2″-terpyridine) ligands give rise to conformationally restricted complexes with iron(II) centres. The absolute configuration of the cations in the diastereomeric ion pairs obtained through the Pfeiffer effect has been calculated using TDDFT methods.

Effective chiral recognition among ions in polar media

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%).

HOMOBIMETALLIC VANADIUM D1-D1 COMPLEXES: STRUCTURE AND MAGNETISM

From Me3SiCC–CCSiMe3 and Ph2PCC–CCPPh2 diynes and vanadocene VCp2, homobimetallic vanadium d1–d1 complexes are synthesized and characterized by X-ray crystal structures of (Cp2V)2(1-2η:3-4η-RCC–CCR), (R = SiMe3 1 PPh2 2); magnetic moments of both complexes from 300 to 2 K indicate an antiferromagnetic J exchange coupling of –10.5 and –59.8 cm–1 for 1 and 2, respectively.

A homobimetallic vanadium d2–d2 complex (Cp2V)2(3η:4η-Me3SiCC–CC–CCSiMe3):structure and magnetism

The d2–d2 homobimetallic complex (Cp2V)2(3η:4η-Me3-SiCC–CC–CCSiMe3) was synthesized from Me3SiCC–CC–CCSiMe3 and Cp2V and characterized by an X-ray crystal structure; magnetic moment measurements from 300 to 2 K indicated a weak antiferromagnetic J exchange coupling of –3.7 cm–1.