Dinuclear zinc(II) double-helicates of homochirally substituted bis(dipyrromethene)s

[structure: see text] A series of bis(dipyrromethene)s substituted with aromatic amide and aliphatic ester homochiral auxiliaries have been prepared and complexed with zinc(II) ions to form double-helical dinuclear complexes. CD analysis of the crude complexes revealed that the helicates formed in a diastereoselective manner. The helicates have been resolved into their constituent M and P helices by HPLC, indicating that the helical sense of the complexes is stable to racemization.     

Highly diastereoselective templated complexation of dipyrromethenes

[reaction: see text] Bis(dipyrromethene)s with relatively long spacers (>5 atoms) form helical monomeric complexes as the two binding units of the bis(dipyrromethene) chelate around the same tetrahedrally coordinated metal ion. Herein we report the first highly diastereoselective mononuclear helicate-forming complexation reactions of bis(dipyrromethene)s using homochiral binol and tartrate motifs which serve as both linkers and asymmetric templates.     

Bis(N‐Confused Porphyrin) as a Semirigid Receptor with a Chirality Memory: A Two‐Way Host Enantiomerization through Point‐to‐Axial Chirality Transfer

The adduct formation of protonated bis(N‐confused porphyrin) (BNCP, 3,3′‐bis(meso‐tetratolyl‐2‐aza‐21‐carbaporphyrin) with chiral anions, carboxylic acids, and alcohols was studied in solution by means of ¹H NMR and circular dichroism (CD) spectroscopic analysis and DFT methods. The addition of enantiopure guests to the acidified BNCP resulted in optical activity that vanished after neutralization. Pairs of the ¹H NMR‐distinguishable diastereomers were formed when enantiopure guests were applied, although a single form was observed upon the addition of the racemic mixtures in each case. Unidirectional configuration change that led to diastereomeric excess was observed in several instances. Such an excess was memorized by metalation of the adducts with AgBF₄, thus resulting in optically active silver(III) complexes of BNCP with some enantiomeric excess. Absolute configurations of BNCP cations and bis(zinc) and bis(silver(III)) complexes were determined on the basis of time‐dependent (TD)‐DFT calculations of their CD spectra. It was shown that some of the chiral carboxylates induced opposite directions of enantiomerization of di‐ and tetracations or di‐/tetracation and bis(zinc) complexes. The source of the optical activity of the equimolar diastereomeric mixture of adducts is discussed.     

Racemic atropisomeric N,N-chelate ligands for recognizing chiral carboxylates via Zn(II) coordination: structure, fluorescence, and circular dichroism

Two racemic atropisomeric N,N'-chelate ligands, bis{3,3'-[N-Ph-2-(2'-py)indolyl]} (1) and bis{3,3'-N-4-[N-2-(2'-py)indolyl]phenyl-2-(2'-py)indolyl} (2), have been found to be able to distinguish the enantiomers of Zn((R)-BrMeBu)2 and Zn((S)-BrMeBu)2 where BrMeBu = O2CCH(Br)CHMe2, with a distinct and intense CD spectral response at approximately the 10 microM concentration range. Computational studies established that the (R)-1-Zn((R)-BrMeBu)2 or (S)-1-Zn((S)-BrMeBu)2 diastereomer is more stable than (R)-1-Zn((S)-BrMeBu)2 or (S)-1-Zn((R)-BrMeBu)2. In addition, computational studies showed that the CD spectra of (S)-1-Zn((S)-BrMeBu)2 and (S)-1-Zn((R)-BrMeBu)2 are similar. (1)H NMR spectra confirmed that these two diastereomers exist in solution in about a 2:1 ratio for both complexes of 1 and 2. The distinct CD response of the racemic ligands 1 and 2 toward the chiral zinc(II) carboxylate is therefore attributed to the preferential formation of one diastereomer. The binding modes of the zinc(II) salt with ligands 1 and 2 were established by the crystal structures of the model compounds 1-Zn(tfa)2 and 2-Zn(tfa)2 (tfa = CF3CO2(-)), where the Zn(II) ion is chelated by the two central pyridyl groups in the ligand. Fluorescent titration experiments with various zinc(II) salts showed that the fluorescent spectrum of the atropisomeric ligand displays an anion-dependent change. The zinc(II) binding strength to the N,N'-chelate site of the atropisomeric ligand has been found to play a key role in the selective recognition of different chiral zinc(II) carboxylate derivatives by the racemic atropisomeric ligands.     

Chasing BODIPY: Enhancement of Luminescence in Homoleptic Bis(dipyrrinato) ZnII Complexes Utilizing Symmetric and Unsymmetrical Dipyrrins

Dipyrromethene metal complexes are fascinating molecules that have applications as light-harvesting systems, luminophores, and laser dyes. Recently, it has been shown that structurally rigid bis(dipyrrinato) zinc(II) complexes exhibit high fluorescence with comparable quantum yields to those of boron dipyrromethenes or BODIPYs. Herein, eight new bis(dipyrrinato) Zn^II complexes, obtained from symmetric and unsymmetrical functionalization of the dipyrromethene structure through a Knoevenagel reaction, are reported. It was possible not only to vary the maximum visible absorption from 490 to 630 nm, but also to enhance the emission quantum yield up to 66 %, which is extraordinarily high for homoleptic bis(dipyrrinato) zinc complexes. These results pave the way for designing highly luminescent bis(dipyrrinato) zinc complexes.     

Isolement de nouveaux complexes de zinc de dipyrrométhènes formés au cours de la synthèse de la méso-tétramésitylporphyrine par la réaction de Rothemund

Three new zinc bis(dipyrromethene) complexes have been isolated in the preparation of meso-tetramesitylporphyrin by the Rothemund zinc template based condensation process.     

Highly diastereoselective and asymmetric Diels-Alder reactions of masked o-benzoquinones with chiral racemic and homochiral furans. Synthesis of optically active tricyclic gamma-lactones

[reaction: see text] The first examples of highly diastereoselective and asymmetric Diels-Alder cycloadditions of in situ generated masked o-benzoquinones (MOBs) with chiral racemic and homochiral furans bearing a chiral center in the alpha-position leading to highly functionalized diastereomeric/enantioselective tricyclic heterocycles and chiral tricyclic gamma-lactones are described.     

A novel method for the preparation of benzylidenecyclohexanes with high optical purity

The enantioselective reaction of the α-thio carbanion derived from 1-phenyl-1-(phenylthio)-1-(tributylstannyl)methane with 4-substituted cyclohexanones in the presence of bis(oxazoline)s gave the products as a diastereomeric mixture. Each diastereomer obtained had high optical purity. The reaction of the α-seleno carbanion derived from the bis(phenylseleno)acetal also showed high enantioselectivity. The stereospecific elimination of the isolated diastereomers on treatment with methanesulfonyl chloride and triethylamine afforded axially chiral benzylidenecyclohexanes with high enantioselectivities up to 99% ee.     

Highly stereoselective addition of silylphosphines to chiral aldehydes

The reaction between diphenyl(trimethylsilyl)phosphine and chiral aldehydes proceeds with high stereoselectivity to give diastereomerically pure tertiary α-trimethylsiloxyalkylphosphines. The diastereomeric purity of the addition products was 90-100%. The products were purified via the formation of borane-phosphine complexes. The reaction of bis(trimethylsilyl)phenylphosphine with acetonide (R)-glyceraldehyde provides tertiary bis(glyceryl)phosphines.     

Homochiral Zn and Cd coordination polymers containing amino acid-tetrazole ligands

The reactions of (S)-3-cyanophenylalanine with NaN(3) in the presence of H(2)O and Lewis acids (ZnCl(2) and CdCl(2)) afford two unprecedented 3D homochiral networks, mono[(S)-5-(3-tetrazoyl)-phenylalaninato]zinc(II) (1) and mono[(S)-5-(3-tetrazoyl)-phenylalaninato]cadmium(II) monoaqua(II) (2), respectively. The two compounds are isostructural with noninterpenetrated SrAl(2) topology. The structure of these coordination polymers gives new insight into Sharpless' reaction of chiral 5-substituted 1H-tetrazole and homochiral supramolecular array constructions.     

(3+3)-Cyclocondensation of the enantiopure and racemic forms of trans-1,2-diaminocyclohexane with terephthaldehyde. Formation of diastereomeric molecular triangles and their stereoselective solid-state stacking into microporous chiral columns

The non-templated reaction of both the homochiral as well as the racemic form of trans-1,2-diaminocyclohexane with terephthaldehyde affords (3+3)-cyclocondensed molecular triangles in practically quantitative yields. The configuration of the diastereomeric products resulting in the individual reactions has been determined by ¹H and ¹³C NMR spectroscopy. Unambiguous proof has been obtained by X-ray crystal structure analysis of both alternative diastereomers, revealing also a stereoselective stacking of the triangles into microporous chiral columns.     

Diasteroselective Addition of Monoand Bis-Silylphosphines to Chiral Aldehydes

Abstract

The addition of silylphosphines to chiral aldehydes proceeds with high diastereoselectivity to give optically pure tertiary α -trimethylsiloxyalkylphosphines. The diastereomeric excesses of the addition products were achieved to 90–100%. The reaction of bis(trimethylsilyl)phenylphosphine with the acetonide of (R)-glyceraldehyde provides diastereomerically enriched tertiary bis(glyceryl)phosphines.     

On the intermediates in chiral bis(oxazoline)copper(II)-catalyzed enantioselective reactions--experimental and theoretical investigations

The intermediates in the chiral bis(oxazoline)copper(II)-catalyzed reactions have been investigated by means of experimental and theoretical investigations. It is shown that the absolute configuration of the hetero-Diels-Alder adduct obtained from the reaction of ethyl glyoxylate with 1,3-cyclohexadiene in the presence of the chiral bis(phenyloxazoline)copper(II) is dependent on the solvent. In this case, a linear relationship between the enantiomeric excess (ee) and the dielectric constant of the solvent was observed. However, the enantiomeric excess for the adduct obtained with the chiral bis(tert-butyloxazoline)copper(II) complex is independent of the solvent. The addition of different coordinating solvents to the chiral catalysts was investigated and no effect on the enantioselectivity of the reaction was observed. A series of chiral bis(tert-butyloxazoline)-, bis(phenyloxazoline)-, and bis(indaneoxazoline)copper(II) complexes has been prepared and characterized by X-ray analysis, and the similarity between the structures is discussed. For comparison, two related chiral bis(tert-butyloxazoline)- and bis(phenyloxazoline)zinc(II) complexes were also prepared and characterized. A series of chiral bis(oxazoline)copper(II)-substrate (the substrate being glyoxal or methyl glyoxylate) complexes was investigated by means of ab initio calculations. Calculation of the total energy of the optimized structure of 17-, 19-, and 21-electron bis(oxazoline)copper(II)-substrate complexes give the 17-electron complex as the most stable and the most reactive complex, while the 21-electron complex is less stable and also much less reactive. The optimized structures of both the 17-electron bis(tert-butyloxazoline)- and bis(phenyloxazoline)copper(II)-substrate complexes show that the plane of the substrate molecule is twisted by approximately 40-45 degrees out of the bis(oxazoline)copper(II) plane, in agreement with the X-ray structures. On the basis of the experimental results, X-ray structures, and ab initio calculations, the structure of the intermediate(s) and reactivity of the chiral bis(oxazoline)copper(II)-substrate complexes are discussed.     

From hetero- to homochiral bis(metallahelicene)s based on a Pt(III)-Pt(III) bonded scaffold: isomerization, structure, and chiroptical properties

Hetero- and homochiral diastereomeric bis(metallahelicene)s have been synthesized. They possess a rare Pt(III)-Pt(III) scaffold bridged by benzoato ligands. It is shown that heterochiral (P,M)-bis(Pt(III)-[6]helicene) can isomerize into the homochiral (P,P)- and (M,M)-bis(Pt(III)-[6]helicene). A theoretical study shows a unique σ-π conjugation between the two π-helices and the σ-Pt(III)-Pt(III) scaffold that impacts the strong chiroptical properties.     

New chiral ligands: 1,4-diols prepared from (<Emphasis Type="Italic">S</Emphasis>)-1-phenylethanol

The stereochemistry of condensation of dilithiated 1-phenylethanol with various carbonyl compounds was investigated. In most cases the reaction proceeds nonstreoselectively, and only in the condensation with PhCOBu-t and 2,4-(MeO)₂C₆H₃COPh only one of the diastereomeric diols prevailed. It was shown by XRD analysis that in the prevailing diastereomeric diol the newly formed chiral carbinol center possessed the same configuration as the initial alcohol. The synthesized diols form homochiral dimers in the crystal lattice.     

Two-dimensional homochiral manganese(II)-azido frameworks incorporating an achiral ligand: partial spontaneous resolution and weak ferromagnetism

By incorporating an achiral diazine ligand, 2-pyridylmethylketazine, which can be locked in a chiral conformation upon coordination, into the manganese(II)-azido system, we induced a homochiral 2D network, in which neighboring Mn(II) ions are bridged via a diazine and two end-on azido ligands into chiral dimeric units, and neighboring units are interlinked via single end-to-end azido bridges. The interdimer chirality preservation is achieved via the homochiral 1D helical linkage formed by Mn(II) and end-to-end azido ions. The 2D layers are stacked in hetero- and homochiral fashion to yield simultaneously racemic and chiral crystals, indicating a partial spontaneous resolution. Both compounds behave as spin-canted weak ferromagnets, but the critical temperatures are different.     

Unexpected influence of stereochemistry on the cytotoxicity of highly efficient Ti(IV) salan complexes: new mechanistic insights

The effect of stereochemistry on the cytotoxicity of highly active and hydrolytically stable N-methylated Ti(IV) salan complexes is reported. Four bis(isopropoxo) complexes incorporating N-methylated salan ligands with different aromatic substitution patterns have been prepared in racemic and optically active forms for the first time by ligand-to-metal chiral induction from trans-diaminocyclohexyl-based chiral ligands. The configuration of the metal center that derives from that of the ligand has an enormous influence on cytotoxicity, with the racemic mixture mostly being more active than the single enantiomers that are of either similar or different activity. This implies that the active species is a salan-bound heterochiral polynuclear compound, interacting with a chiral target. Four additional complexes of achiral salan and chiral labile sec-butoxo ligands, analyzed as racemic and as homochiral, revealed no influence of stereochemistry, supporting early dissociation of the labile ligands to give the polynuclear products.     

Asymmetric Mannich-type reactions for the synthesis of aspartic acid derivatives from chiral N-tert-butanesulfinylimino esters

Addition of ketene acetals to sulfinimines derived from homochiral N-tert-butanesulfinamide using various Lewis acids furnishes derivatives of aspartic acid in diastereomeric ratios up to 97:3. Following an easy removal of the N-tert-butanesulfinyl chiral auxiliary, optical active beta-amino esters are obtained.     

Nuclear magnetic resonance studies of helical dipyrromethene-zinc complexes

[formula: see text] Analysis of helical chirality within dinuclear dipyrromethene-Zn(II) complexes has been achieved with the use of 1H NMR spectroscopy. The use of AgFOD and chiral lanthanide shift reagents gives fully resolved resonances attributable to two diastereomeric helical complexes.     

Synthesis of Chiral Labtb and Visualization of Its Enantiomeric Excess by Induced Circular Dichroism Imaging

Crystalline particles of a microporous, robust, and chiral metal–organic framework (MOF) were synthesized and their enantiomer excess (ee) was visualized for each microparticle by CD imaging. Labtb, a thermally and chemically robust MOF, was employed in this study because it shows a chiral space group. Although Labtb has been obtained as a racemic conglomerate, enantioselective synthesis of Labtb was achieved via a chiral precursor complex consisting of lanthanum and homochiral phenylalanine. Methyl orange (MO) was introduced into the micropores of chiral Labtb, which showed a strong induced CD signal for the absorption band of MO chromophores. High ee of the chiral Labtb was revealed by microscopic CD observation at the particle-level. This result provides a facile way to obtain a robust MOF that has chiral nanospace.