Chiral Zn Research Articles

Circularly polarized (CP) green-light of two chiral Zn(II)-Tb(III)-Salen heterobinuclear enantiomers

Despite the appreciable high color-purity green-light of chiral Tb3+-complexes, it remains a great challenge to enable their both high quantum efficiency and large circularly polarized light (CPL) activity. Herein, through the self-assemble of the chiral Salen-type bis-Schiff-base ligand (S,S)-H2L or (R,R)-H2L with Zn(OAc)2·2H2O and Ln (NO3)3·6H2O (Ln = La, Tb, Gd), two series of chiral Zn(II)-Ln (III)-heterobinuclear enantiomers [Zn ((S,S)-L)Ln (μ1-OAc)(μ2-NO3)2] (Ln = La, 1; Tb, 2; Gd, 3) or [Zn ((R,R)-L)Ln (μ1-OAc)(μ2-NO3)2] (Ln = La, 4; Tb, 5; Gd, 6) were afforded, respectively. Photophysical study shows that the destabilized 3π-π* energy level upon Zn2+ coordination, is confirmed to effectively sensitize of the Tb3+-centered green-light for the two chiral complexes [Zn ((S,S)-L)Tb (μ1-OAc)(μ2-NO3)2] (2) and [Zn ((R,R)-L)Tb (μ1-OAc)(μ2-NO3)2] (5). The merits of efficient (ΦTbL = 5.6–6.2 %) Tb3+-centered green-light and strong CPL activity (|gPL| = 0.03, 5D4→7F3 transition), engender chiral Zn(II)-Tb(III)-Salen complexes like 2 and 5 a new platform to ideal chiral organo-Tb3+ candidates.

Aggregation-induced enhanced fluorescence emission of chiral Zn(II) complexes coordinated by Schiff-base type binaphthyl ligands.

A pair of novel chiral Zn(II) complexes coordinated by Schiff-base type ligands derived from BINOL (1,1'-bi-2-naphthol), R-/S-Zn, were synthesized. X-ray crystallography revealed the presence of two crystallographically independent complexes; one has a distorted trigonal-bipyramidal structure coordinated by two binaphthyl ligands and one disordered methanol molecule (molecule A), while the other has a distorted tetrahedral structure coordinated by two binaphthyl ligands (molecule B). Numerous CH⋯π and CH⋯O interactions were identified, contributing to the formation of a 3-dimensional rigid network structure. Both R-/S-Zn exhibited fluorescence in both CH2Cl2 solutions and powder samples, with the photoluminescence quantum yields (PLQYs) of powder samples being twice as large as those in solutions, indicating aggregation-induced enhanced emission (AIEE). The AIEE properties were attributed to the restraint of the molecular motion arising from the 3-dimensional intermolecular interactions. CD and CPL spectra were observed for R-/S-Zn in both solutions and powders. The dissymmetry factors, gabs and gCPL values, were within the order of 10-3 to 10-4 magnitudes, comparable to those reported for chiral Zn(II) complexes in previous studies.

Sustainable approach for the synthesis of chiral β-aminoketones using an encapsulated chiral Zn(ii)–salen complex

To enable sustainable chemical transformations, it is imperative to adopt ecofriendly strategies aligned with economic growth and environmental preservation.

Effect of calcination temperature on the morphology and catalytic properties of ZnO nanostructures fabricated from a chiral precursor for photodegradation of both cationic and anionic dyes

A chiral Zn MOF is fabricated into ZnO microflowers, polyhedrons and nanorods at three different temperatures and these are utilized for the photodegradation of methylene blue and Congo red.

Novel noncentrosymmetric polar coordination compounds derived from chiral histidine ligands

Noncentrosymmetric chiral Zn- and Cd-coordination compounds have been synthesized by a slow evaporation method using histidine under acidic conditions.

Evaluation of Zn2+ Coordination Structures in Chiral Zn2+ Complexes Based on Shape Measurement Factors: Relationships between Activity and the Coordination Structure

We previously reported on enantioselective aldol reactions of acetone and cyclic ketones with benzaldehyde derivatives catalyzed by chiral Zn2+ complexes that mimic class II aldolases. The results and mechanistic studies indicated that the catalytic activity of Zn2+ complexes is dependent not only on the coordination numbers of Zn2+ but also on its coordination structure. In this study, we report on shape measures (abbreviated as S values in this manuscript) of such Zn2+ complexes with respect to the 5‐coordination structure based on calculations with continuous shape measures (CShM) using their crystal structures. The S values of Zn2+ ions in Zn2+ complexes for trigonal bipyramidal (D3h) or square pyramidal (C4v) structures suggest that Zn2+ ions in the catalytically active Zn2+ complexes possess D3h and C4v structures, while Zn2+ ions in the unreactive Zn2+ complex has a C4v structure. Moreover, the S values of Zn2+ were calculated with respect to 6‐coordination geometry, based on the assumption that aldol reactions proceed via 6‐membered transition states, and it was implied that 6‐coordinated Zn2+ ions in aldol‐active Zn2+ complexes prefer an octahedron structure (Oh). These results for the S values of Zn2+ ions in the active Zn2+ complexes and those for complexes reported by other research groups suggest that the transition of 5‐coordinated D3h to the 6‐coordinated Oh structure is essential for achieving catalytic stereoselective aldol reactions.

Synthesis and Aggregation Studies of Functional Binaphthyl-Bridged Chiral Phthalocyanines.

We describe the preparation of a battery of chiral Zn(II) phthalocyanines with an AABB substitution pattern through cross-condensation of different chiral, binaphthyloxy-linked bisphthalonitriles and (non)functionalized single phthalonitriles. All the compounds are endowed with reactive groups (halogen and/or ethynyl moieties) that will allow us to prepare customized amphiphilic phthalocyanines. Preliminary self-assembly studies in solution have been performed by UV-vis and circular dichroism experiments.

Complexation of Chiral Zinc(II) Porphyrin Tweezer with Achiral Aliphatic Diamines Revisited: Molecular Dynamics, Electronic CD, and 1H NMR Analysis.

We have reported here the complexation and chiroptical behavior of the host-guest complexes using a new chiral Zn(II) bisporphyrin tweezer host and a series of achiral aliphatic diamine guests varying the chain length. (1R,2R)-Cyclohexanediamine covalently links two Zn(II) porphyrin moieties, which thereby produces a strong chiral field around the bisporphyrin tweezer framework. The chiral tweezer upon complexation with achiral guest exhibited large changes in the UV-vis spectra and CD exciton couplets due to a sudden change in the porphyrin disposition, which is controlled by the host-guest stoichiometry as well as the chain lengths of the diamine guest. Addition of smaller diamines (n: 2-5) to the host resulted in the formation of 1:1 sandwich and 1:2 open complexes, respectively, at the low and high guest concentration, which eventually display two-step inversions of the CD couplet. With longer diamines (n: 6-8), however, only 1:1 sandwich complexes are formed with retention of the CD sign. Similar observations were also reported by us recently using another chiral bisporphyrin tweezer having (1R,2R)-diphenylethylenediamine as the spacer. In an effort to obtain deeper insights into the sudden changes of interporphyrin disposition just by changing the length of the achiral diamines, we have extended a series of computational studies and correlated closely with the results obtained from the experiment. While the previously published study has relied on commonly applied Monte Carlo (MC) sampling of the potential energy surface in addition to being guided by porphyrin effective transition moment approximation, the present study uses a considerably more robust molecular modeling protocol, namely Molecular Dynamics (MD) simulations followed by full ab initio geometry optimization and TD-DFT CD prediction. The experimental data corroborate with the results obtained from the theoretical conformational analysis. The latter are also supported by experimental 1H NMR data empowered by the porphyrin ring-current effect. The NMR spectral patterns of pyrrolic protons of the free host and the 1:1 sandwich complexes appear very diagnostic and reflect the changes in the mutual porphyrin disposition on moving from the free host to the complexed ones with short and long diamines. Overall, the experimental NMR data underscore the sensitivity of pyrrolic protons chemical shifts to subtle alterations of the geometrical features, and as such, they come in agreement with the theoretically derived models.

Zn‐Catalyzed Diastereo‐ and Enantioselective Dearomative [3+2] Cycloaddition Reaction of 2‐Nitroindoles and 2‐Nitrobenzothiophenes

AbstractAn efficient asymmetric dearomative [3+2] cycloaddition reaction of 2‐nitroindoles and 2‐nitrobenzothiophenes with 3‐isothiocyanato oxindoles was developed by using a chiral Zn(OTf)2/bis(oxazoline) complex as a catalyst. With the developed protocol, a range of enantioenriched complex heterocyclic compounds containing three contiguous stereocenters, one of which is spirocyclic center, could be obtained in quantitative yields with excellent diastereo‐ and enantioselectivities. The potential utility of this method was showcased by the diverse transformations of the products.magnified image

Zinc‐Catalyzed Enantioselective Dearomative [3+2] Cycloaddition Reaction of 3‐Nitrobenzothiophenes and 3‐Nitrothieno[2,3‐b]yridine with 3‐Isothiocyanato Oxindoles

AbstractA highly diastereo‐ and enantioselective dearomative [3+2] cycloaddition reaction of 3‐nitrobenzothiophenes and 3‐nitrothieno[2,3‐b]with 3‐isothiocyanato oxindoles is developed. The reaction is catalyzed by the chiral Zn(OTf)2/bis(oxazoline, and is the second example of a catalytic asymmetric dearomative cycloaddition reaction of 3‐nitrobenzothiophene derivatives. A range of complex heterocyclic compounds containing three contiguous stereocenters, one of which is spirocyclic center, can be obtained in quantitative yields with excellent stereoselectivities.magnified image

Selective chiral symmetry breaking and luminescence sensing of a Zn(ii) metal-organic framework.

The chiral Zn(ii) metal-organic framework [(CH3)2NH2]5[Zn1.5(Zn3O)(TATAT)2]·9DMF·17H2O (1) has been prepared from achiral precursors Zn(NO3)2·6H2O and 5,5',5''-(1,3,5-triazine-2,4,6-triyl)tris(azanediyl)triisophthalate (H6TATAT) in a solvent mixture of DMF/MeOH/H2O/HCOOH without any chiral sources. In particular, the non-random handedness excess (1P ≫ 1M) was generated and was verified by single-crystal X-ray diffraction and solid-state circular dichroism spectroscopy. Furthermore, complex 1 displays high selectivity and sensitivity for detecting Fe3+ and is found to be an excellent chemical sensor for detecting nitro explosives especially 3-nitrophenol.

Complexation of Chiral Zinc-Porphyrin Tweezer with Achiral Diamines: Induction and Two-Step Inversion of Interporphyrin Helicity Monitored by ECD.

We report here the synthesis of a new chiral Zn(II) bisporphyrin tweezer in which two achiral Zn(II) porphyrin moieties are covalently linked by (1R,2R)-diphenylethylenediamine, which produces a strong chiral field around the porphyrin moieties. The chiral tweezer exhibits not only intensity modulation in UV-vis and CD exciton couplets but also a dramatic change, namely, the inversion in the sign of the interporphyrin helicity upon binding of achiral diamines of varying lengths. The stoichiometry-controlled formation of a 1:1 sandwich complex followed by a 1:2 open complex was realized with smaller achiral diamines (n: 2-5) at their low and high concentration regions, respectively, leading to two-step inversion of chirality. With longer achiral diamines (n: 6-8), however, only 1:1 sandwich complexes are formed with no change of sign in the CD couplet. As compared to a 1:2 open complex, a 1:1 sandwich complex shows an enhanced CD response as two porphyrin units come closer in space. Structural insights of the host-guest complexes have been obtained spectroscopically along with molecular mechanics minimizations with the newly implemented OPLS-3 force field followed by geometry optimization using density functional theory of the most stable conformer. The amide bridge in the Zn(II) bisporphyrin has a low rotational barrier, which provides conformational flexibility to change interporphyrin helicity between 1:1 and 1:2 binding depending on the size of the achiral guests in order to minimize host-guest steric interactions.

The theoretical interpretation of the Linear/circularly polarized light-induced molecular orientation of the azo group-containing trans-Achiral Schiff base dinuclear complex composite material

We have investigated linearly polarized UV and circularly polarized UV light-induced molecular orientation, namely increasing optical anisotropy of newly synthesized AZ containing chiral Schiff base Ni (II), Cu (II) and Zn (II) complexes, as organic/inorganic hybrid materials in polymethylmethacrylate (PMMA) cast films. The driving force and reason for polarized UV light-induced molecular orientation of AZ is so-called Weigert effect. The increase of the dichroic was measured with polarized absorption electronic spectra. In addition, we study on newly synthesized composites of AZ containing chiral Schiff base metal complexes with AZ to irradiate with not only linearly but also circularly polarized UV light (Wavelength selective (260, 318(π-π* of AZ) and 380 nm) and continuous wavelength). In addition, we comparison between simulated by TD-DFT and experimental spectra of electronic and CD spectra, and we calculated dipole moments by TD-DFT. Furthermore, we are using the CD spectrum after circularly polarized light UV irradiation, tried to observation change of supramolecular chiral order of the complexes.

ChemInform Abstract: A Novel and Efficient Methodology for Thio‐Michael Addition in the Synthesis of cis‐β‐Thio‐α‐aminoacid Derivatives Using Zn[(L)‐Pro]2 as Heterogeneous Catalyst.

A simple, efficient and green chemical ultrasound assisted thio-Michael addition reaction between thiols and (Z)-azlactones aiming to produce non-natural amino acid derivatives by using chiral Zn[(L)-Pro]2 as a heterogeneous catalyst is herein described. The product was obtained in good to excellent yields presenting high diastereoselectivity.

Chiral Nanozymes-Gold Nanoparticle-Based Transphosphorylation Catalysts Capable of Enantiomeric Discrimination.

Enantioselectivity in RNA cleavage by a synthetic metalloenzyme has been demonstrated for the first time. Thiols containing chiral Zn(II) -binding head groups have been self-assembled on the surface of gold nanoparticles. This results in the spontaneous formation of chiral bimetallic catalytic sites that display different activities (kcat ) towards the enantiomers of an RNA model substrate. Substrate selectivity is observed when the nanozyme is applied to the cleavage of the dinucleotides UpU, GpG, ApA, and CpC, and remarkable differences in reactivity are observed for the cleavage of the enantiomerically pure dinucleotide UpU.

Chirality of self-assembled achiral porphyrins induced by chiral Zn(ii) Schiff-base complexes and maintained after spontaneous dissociation of the templates: a new case of chiral memory

Herein, we exploit the induction of chirality by chiral Zn(ii) Schiff-base complexes, followed by their spontaneous dissociation in aqueous solution, providing for the first time a possibility of overcoming the template removal steps, to demonstrate memorization of chirality in porphyrin hetero-aggregates.

A novel and efficient methodology for thio-Michael addition in the synthesis of cis-β-thio-α-aminoacid derivatives using Zn[(l)-Pro]2as heterogeneous catalyst

A simple, efficient and green chemical ultrasound assisted thio-Michael addition reaction between thiols and (Z)-azlactones aiming non-natural amino acid derivatives using chiral Zn[(l)-Pro]2as a heterogeneous catalyst is herein described.

Triflate-functionalized calix[6]arenes as versatile building-blocks: application to the synthesis of an inherently chiral Zn(ii) complex.

Cavity-based metal complexes can find many applications notably in the fields of catalysis and biomimicry. In this context, it was shown that metal complexes of calix[6]arenes bearing three aza-coordinating arms at the small rim provide excellent structural models of the poly-imidazole sites found in the active site of many metallo-enzymes. All these N-donor ligands were synthesized from the 1,3,5-tris-methoxy-p-tBu-calix[6]arene platform, which presents some limitations in terms of functionalization. Therefore, there is a need for the development of new calix[6]arene-based building-blocks selectively protected at the small rim. Herein we describe the regioselective one step synthesis of two calix[6]arenes decorated with triflate groups, i.e. X6H4Tf2 and X6H3Tf3, from the parent calix[6]arene X6H6. It is shown that the triflate groups can either act as protecting or deactivating groups, allowing the elaboration of sophisticated calixarene-based systems selectively functionalized at the large and/or at the small rim. In addition, X6H3Tf3 is functionalized on the A, B, and D rings and thus gives access to inherently chiral compounds, as demonstrated by the synthesis of a rare example of inherently chiral cavity-based metal complex.

Enantioselective Hydrosilylation of Imines Catalyzed by Chiral Zinc Acetate Complexes.

A series of zinc acetate complexes with optically pure diphenylethanediamine (DPEDA)-derived ligands have been employed as enantioselective catalyst for the hydrosilylation of various imines. High control of stereoselectivity (up to 97% ee) and excellent yields (up to 96%) were gained for a broad range of N-phosphinoylimines by using (R,R)-N,N'-dibenzyl-1,2-diphenylethane-1,2-diamine. This is the first successful application of an air-stable and environmentally friendly chiral Zn(OAc)2 complex instead of the previously used harmful diethylzinc in the asymmetric reduction of the C═N double bond.

Zn-Catalyzed Diastereo- and Enantioselective Cascade Reaction of 3-Isothiocyanato Oxindoles and 3-Nitroindoles: Stereocontrolled Syntheses of Polycyclic Spirooxindoles.

A catalytic asymmetric Michael/cyclization cascade reaction of 3-isothiocyanato oxindoles and 3-nitroindoles has been disclosed with a chiral Zn(OTf)2/diphenylamine-linked bis(oxazoline) complex as the catalyst. A range of enantioenriched polycyclic spirooxindole derivatives containing three contiguous stereocenters were efficiently constructed in quantitative yields with excellent diastereo- and enantioselectivities. Importantly, the metal catalytic strategy in this work is significantly superior to the previous organocatalytic method in the diastereo- and enantioselectivities for almost all of the examined cases.