Synthesis and Stereochemical Properties of Chiral Square Complexes of Iron(II)

Der hexadentate und ditopische Ligand 2,5-Bis([2,2']bipyridin-6-yl)pyrazin bildet bei der Selbstorganisationsreaktion mit Fe²⁺-Ionen einen chiralen, quadratförmigen Tetramerkomplex. Das Racemat dieses Komplexes wurde mit Hilfe von Antimonyltartrat in die Enantiomere getrennt. Die Reinheit des Enantiomers wurde durch NMR-Spektroskopie unter Zuhilfenahme eines chiralen, diamagnetischen Shift-Reagenzes untersucht, wie auch duch die Beobachtung des Circulardichroismus (CD). Das CD-Spektrum wurde zudem mit zeitabhängiger Dichtefunktionaltheorie berechnet, wobei die vorhergesagte Korrelation zwischen CD-Spektrum und Konfiguration des Komplexes durch Röntgenstrukturanalyse bestätigt wurde. Die Verwendung einer chiralisierten Variante des Liganden ergab den entsprechenden Eisenkomplex in diastereomerenreiner Form.The hexadentate, and ditopic ligand 2,5-bis([2,2']bipyridin-6-yl)pyrazine yields a chiral, tetrameric, square-shaped, self-assembled species upon complexation with Fe²⁺ ions. The racemate of this complex was resolved with antimonyl tatrate as the chiral auxiliary. The purity of the enantiomer was determined by NMR spectroscopy, by using a chiral, diamagnetic shift reagent, and by circular dichroism (CD). The CD spectrum was also calculated by time-dependent density functional theory, and the correlation that was found between CD spectrum and configuration was confirmed by X-ray cristallography. When a chiralised version of the ligand was used instead, the corresponding iron complex was obtained in diastereomerically pure form

Efficient Resolution of Dinuclear Triple Helicate By Asymmetric Extraction/Precipitation Using TRISPHAT Anions as Resolving Agents

Tetradentate 1,2-bis[4-(4´-methyl-2,2´-bipyridyl)]ethane ligand (3) and Fe(NH4)2(SO4)26 H2O combine in a 3:2 ratio to form the racemic helicate [Fe2L3]4+ (4), as reported by Elliott et al. We now show that the enantiomeric purity of 4 can be efficiently measured by 1H NMR by the use of the TRISPHAT (1) salt as a chiral shift reagent. Large differences in chemical shifts (δδ of up to 0.3 ppm, 20 % [D6]DMSO in CD3CN) are observed between the enantiomers of 4 upon addition of [nBu4N][-1]. The resolution of 4 by asymmetric extraction was attempted: addition of an organic solution of [cinchonidinium][δ-1] salt (2 equiv) to an aqueous solution of helicate 4-(SO4)2 led, after vigorous stirring, to the extraction of the homochiral diastereomer [P-4][δ-1]4 into the organic layer along with the precipitation of the heterochiral diastereomer [M-4][δ-1]4 at the interface (diastereomeric ratio>49:1 for both processes). An enantioenriched fraction of [P-4][SO4]2 remained in the aqueous layer. To obtain only two fractions of resolved helicate and develop this procedure into an efficient resolution protocol, four equivalents of [cinchonidinium][δ-1] salt were used as the resolving agent. Chemically and diastereomerically pure [P-4][δ-1]4 and [M-4][δ-1]4 helicate salts were then obtained in excellent yields

Supramolecular Stereocontrol of Octahedral Metal-Centered Chirality. Ligand Modulation

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)

Configurational Ordering of a Cationic Dinuclear Triple Helicate by Chiral TRISPHAT Anions

Chiral TRISPHAT anions behave as efficient asymmetric hosts controlling with high efficiency the configuration of a cationic dicobalt(II) triple helicate—de up to 82%

Chiral Hexacoordinated Phosphorus Anions: Effective Auxiliaries for Anion Mediated Asymmetric Processes

Easily synthesized and resolved TRISPHAT anion is an efficient chiral auxiliary for asymmetric processes with chiral cations

Simple Ion Exchange Procedure of Common Anions to TRISPHAT. Application to the Purification of Cationic Species

Triarylcarbenium, monomethine cations are poorly retained on polar chromatographic phases when associated with TRISPHAT as counterion as opposed to classical anions. This allows an easy separation and purification of these organic cationic salts

Diastereoselektive Ionenpaarbildung des TRISPHAT-Anions mit Tris(4,4'-dimethyl-2,2'-bipyridin)eisen(II)

Zwei konfigurativ stabile, chirale Anionen (TRISPHAT 1) beeinflussen bei der Ionenpaarbildung mit einem konfigurativ labilen Eisen(II)-Komplex dessen Konfiguration mit hoher Diastereoselektivität (>96 % de). Dabei steigt der Diastereomerenüberschuß mit abnehmender Lösungsmittelpolarität.Two configurationally stable, chiral anions (TRISPHAT, 1) behave as efficient hosts that control the configuration of a configurationally labile iron(II) complex as the guest with high diastereoselectivity (>96 % de) upon ion pairing. The diastereoselectivity increases with decreasing solvent polarity