Homochiral Ligands Research Articles

Halide-assisted differential growth of chiral nanoparticles with threefold rotational symmetry

Enriching the library of chiral plasmonic nanoparticles that can be chemically mass-produced will greatly facilitate the applications of chiral plasmonics in areas ranging from constructing optical metamaterials to sensing chiral molecules and activating immune cells. Here we report on a halide-assisted differential growth strategy that can direct the anisotropic growth of chiral Au nanoparticles with tunable sizes and diverse morphologies. Anisotropic Au nanodisks are employed as seeds to yield triskelion-shaped chiral nanoparticles with threefold rotational symmetry and high dissymmetry factors. The averaged scattering g-factors of the l- and d-nanotriskelions are as large as 0.57 and − 0.49 at 650 nm, respectively. The Au nanotriskelions have been applied in chiral optical switching devices and chiral nanoemitters. We also demonstrate that the manipulation of the directional growth rate enables the generation of a variety of chiral morphologies in the presence of homochiral ligands.

Macroscopic handedness inversion of terbium coordination polymers achieved by doping homochiral ligand analogues.

Inspired by natural biological systems, chiral or handedness inversion by altering external and internal conditions to influence intermolecular interactions is an attractive topic for regulating chiral self-assembled materials. For coordination polymers, the regulation of their helical handedness remains little reported compared to polymers and supramolecules. In this work, we choose the chiral ligands R-pempH2 (pempH2 = (1-phenylethylamino)methylphosphonic acid) and R-XpempH2 (X = F, Cl, Br) as the second ligand, which can introduce C-H⋯π and C-H⋯X interactions, doped into the reaction system of the Tb(R-cyampH)3·3H2O (cyampH2 = (1-cyclohexylethylamino)methylphosphonic acid) coordination polymer, which itself can form a right-handed superhelix by van der Waals forces, and a series of superhelices R-1H-x, R-2F-x, R-3Cl-x, and R-4Br-x with different doping ratios x were obtained, whose handedness is related to the second ligand and its doping ratio, indicating the decisive role of interchain interactions of different strengths in the helical handedness. This study could provide a new pathway for the design and self-assembly of chiral materials with controllable handedness and help the further understanding of the mechanism of self-assembly of coordination polymers forming macroscopic helical systems.

Homochiral Ferromagnetic Coupling Dy2 Single-Molecule Magnets with Strong Magneto-Optical Faraday Effects at Room Temperature.

By the bridging action of the 6-chloro-2-hydroxypyridine (Hchp) ligand and the terminal coordination role of the homochiral ligand, (-)/(+)-3-trifluoroacetyl camphor (l-Htfc/d-Htfc), a pair of enantiomerically pure dysprosium(III) dinuclear complexes, [Dy2(l-tfc)4(chp)2(MeOH)2] (l-1) and [Dy2(d-tfc)4(chp)2(MeOH)2] (d-1), was obtained. Their circular dichroism (CD) spectra verified their enantiomeric nature. Magnetic investigation indicated that they exhibit ferromagnetic interaction and good zero field single-molecule magnet (SMM) properties. The Ueff/k values of l-1 and d-1 at 0 Oe are 180.5 and 181.3 K, respectively, which are large values for homochiral Dy(III) SMMs. A reasonable explanation for the magnetic properties of l-1 and d-1 was supplied by ab initio calculations. Remarkably, magnetic circular dichroism (MCD) investigation revealed that the chiral Dy2 enantiomers show a strong magneto-optical Faraday effect at room temperature, suggesting potential applications in magneto-optical devices.

Synthesis, crystallographic and spectral studies of homochiral cobalt(II) and nickel(II) complexes of a new terpyridylaminoacid ligand

Based on a chiral terpyridylaminoacid ligand, a series of homochiral Co(II) and Ni(II) complexes, namely, [Co(H2L)(HL)]·Cl·(PF6)2·2H2O (1), [Ni(H2L)(HL)]·Cl·(PF6)2 (2), [Co2(L)2(CH3OH)(H2O)]·(PF6)2·CH3OH (3), [Ni2(L)2(CH3OH)2]·(PF6)2·2CH3OH (4), [Co2(L)2(N3)2]·3H2O (5), and [Ni2(L)2(SCN)2]·4H2O (6) have been successfully synthesized and characterized by elemental analysis, TGA, spectroscopic methods (IR, CD and electronic absorption spectra) and single-crystal X-ray diffraction structural analysis (HL = (S)-2-((4-([2,2':6′,2″-terpyridin]-4′-yl)benzyl)amino)-4-methylpentanoic acid). In the acidic reaction conditions, one protonated (H2L)+ and one zwitterionic HL only used their terpyridyl groups to chelate one metal ion Co(II) or Ni(II), forming chiral mononuclear cationic complexes 1 or 2. But in the basic and hydro(solvo)thermal reaction conditions, deprotonated ligands (L)‒ acting as bridges used their terpyridyl and amino acid groups to link with two Co(II) or Ni(II) ions, fabricating chiral dinuclear metallocyclic complexes 3–6. Those chiral mononuclear and dinuclear complexes whose chirality originates in the homochiral ligand HL further self-assemble into higher-dimensional homochiral supramolecular frameworks through intermolecular hydrogen-bonding and π···π interactions. Notably, the coordination mode, hydrogen-bonding site, and existence form of HL ligand can be controlled by the protonation of its amino group, and the architectural diversity of those supramolecular frameworks is adjusted by pH and counter anions. Very interestingly, the 3D porous supramolecular frameworks built up from the huge chiral mononuclear cationic complexes 1 and 2 have novel helical layers only formed through every right-handed helical chain intertwining with two adjacent same helical chains, and the 2D supramolecular helicate 5 consists of two types of left-handed helical chains.

Synthesis of l-azaisotryptophan and its analogs: a general access to new 2-substituted azaindoles

l-(N-Cbz)-7-azaisotryptophan, l-(N-Cbz)-1a, a new isostere of tryptophan, was synthesized by reacting Li2-(N-Boc)-2-amino-3-picoline, Li2-(N-Boc)-2a, with appropriately protected l-aspartic acid followed by simple functional group manipulation. This synthetic success led us to access a set of analogs of azaisotryptophan (4a–c; 6a–c) as well as a new class of chiral amines (7a–c; 8a–c) for future application in asymmetric synthesis and design of homochiral ligands. Further, we have generalized the method substantiating a variety of new azaindol-2-yl derivatives (10aa–10lc) with functionalized substituents. In a preliminary luminescence characterization, l-(N-Cbz)-1a has exhibited about 30nm bathochromic shifted fluorescence emission compared to tryptophan and (N-Cbz)-tryptophan.

Half-sandwich rhodium and iridium complexes containing homochiral imidazolyl-imine ligands: synthesis, characterization and catalytic applications

Condensation of homochiral primary amines with 1-methyl-1H-imidazole-2-carbaldehyde affords the corresponding imidazolyl-imine compounds (L1-L3) which have been employed as ligands for the preparation of half-sandwich rhodium and iridium complexes of the formula [(η(5)-C5Me5)MClLn][SbF6]. Treatment of these chloride compounds with AgSbF6 renders dicationic aqua-complexes [(η(5)-C5Me5)MLn(H2O)] [SbF6]2 which act as catalysts for the Diels-Alder reaction between methacrolein and cyclopentadiene. Catalysis occurs with good exo:endo selectivity and poor enantioselectivity. All the compounds have been completely characterized by analytical and spectroscopic methods. Characterization includes the molecular structure determination of the complexes [(η(5)-C5Me5)MClLn][SbF6] (Ln = L1, M = Rh, (1) Ir (4); Ln = L3, M = Ir (6)) and [(η(5)-C5Me5)ML1(H2O)][SbF6]2 (M = Rh (7), Ir (10)) using X-ray diffraction. From the stereochemical properties of the organometallic precursors the catalytic outcome is discussed.

New chiral coordination polymers constructed from well elaborated achiral and chiral ligands

The elaboration of structurally related tetrazolate-based ligands from achiral to chiral led to the formation of two new chiral coordination polymers (CCPs). Compound 1 contains an infinite 1D zigzag Hg chain and a 1D helical water chain, its chirality is induced by the symmetry breaking of an achiral ligand while compound 2 is a 3D framework with a new 3-connected structural topology constructed from a homochiral ligand. The chiral natures of the two CCPs were both confirmed by circular dichroism (CD) spectra. The luminescent properties of compounds 1 and 2 were also investigated. Their strong luminescence suggest that both compounds may be excellent candidates as potential photoactive materials.

Near achiral metal–organic frameworks from conformationally flexible homochiral ligands resulted by the preferential formation of pseudo-inversion center in asymmetric unit

A near identical MOF from the reaction between a homochiral ligand and LaIII ion to that from racemic ligand was obtained due to the preferential formation of the pseudo-centrosymmetric arrangement in asymmetric units.

ChemInform Abstract: Enantioselective Synthesis of Deltacyclenes Using a (CoI2:Zn) Catalytic System.

Abstract The efficient chiral catalyst [CoI 2 ;Zn/(L*) n ] readily promotes the homo Diels-Alder reactions between norbornadiene 1 and alkynes 2 , affording tetracyclic compounds called “deltatcyclenes” 3 . In this [2+2+2) cycloadditions, stereochemical control is achieved through the presence of catalytic amount of homochiral mono and bidentate ligands leading to deltacyclenes in high chemical and optical yields.

Chiral heterocyclic ligands. XVI: Synthesis and crystal structures of four metal complexes of a tridentate, biheterocyclic ligand derived from l-cysteine

The readily available homochiral ligand ( 1) was used to prepare four mononuclear nickel and cobalt complexes with a 2:1 ligand:metal ratio. X-ray crystal structures of these revealed that in all cases the N,N,O-tridentate ligand adopts facial coordination to the metal with the pyridine rings trans-disposed and the carboxylate and amine groups cis. The individual crystal structures of these compounds differ significantly in the way the complexes pack, which is mediated by hydrogen bonding involving the cations, anions and water molecules as well as, in one case, π-stacking.

Ligand-assisted, copper-catalyzed enantioselective benzylic amination

Several classes of ligands, including α-amino acids, diamines, diphosphines, bis-oxazolines, and diimines, support efficient copper-catalyzed amination of benzylic hydrocarbons by anhydrous chloramine-T. Catalysts derived from homochiral ligands, particularly chiral diimines, effect aminosulfonation with low to moderate enantioselectivity.

Mn(II)-Binaphthalenyl Dicarboxylate Complexes: Helical Rectangular Tubes, (4,4) Grid Chiral Layer and Three-Dimensional Cubic Diamond Frameworks

Reactions of 2,2′-dihydroxyl-[1,1′]-binaphthalene-3,3′-dicarboxylate acid (H2bna) with manganese chloride by a solvent or solvothermal method in the presence of pyridine (py) or 4-picoline (pic) give birth to three 1D to 3D frameworks: [Mn(bna)(DMF)2(H2O)2]n·nDMF (1), {(Hpic)2[Mn3(bna)4(C2H5OH)2(H2O)2]·5H2O}n (2), and {(Hpy)2[Mn3(bna)4(py)2(H2O)2]·4H2O}n (3) (DMF = N,N′-dimethylformamide). Crystal structure analyses reveal that 1 is a mesomer with equivalent R- and L-helical rectangular tubes constructed from homochiral ligands, which is further assembled into a 3D supramolecular network through hydrogen bonds and C−H···π interactions. Complex 2 consists of a (4,4) grid chiral layer structure, while 3 features a 3D cubic diamond network with Schlafli symbol 66 topology, though they both comprise of [Mn3(μ2-COO)6(COO)2] pinwheel molecular building blocks which act as 4-connected nodes and bna2− as linkers. Magnetic studies indicate that antiferromagnetic couplings exist in both 2 and 3.

Solvothermal syntheses and structures of indium(III)-binaphthalenyl dicarboxylate complexes with yellow/blue luminescence

Two novel In(III) complexes, [In(bna)(Hbna)] n ( 1) and [In 2(bna) 2( μ 2-OH) 2] n ·4 nH 2O ( 2) (H 2bna=2,2′-dihydroxy-1,1′-binaphthyl-3,3′-dicarboxylate acid), have been reported. Complex 1 adopts a 2D layer structure, where each layer composed from homochiral ligands is chiral while the ligands in two neighboring layers are enantiomer. Complex 2 is constructed by individual –In–O–In– chains, which are further connected by bna 2− into a 3D honeycomb framework. As a derivative of H 2bna ligand, dmbna ( 3) was recrystallized for structurally comparison with 1- 2 (dmbna=dimethyl 2,2′-dihydroxy-1,1′-binaphthyl-3,3′-dicarboxylate). X-ray powder diffractions (XRD) and thermogravimetric analyses (TGA) for 1-2 show that they are highly thermally stable in the solid state. Complexes 1 and 2 exhibit the intense yellow luminescence at 573 nm and blue luminescence at 459 nm at room temperature, respectively. And an astonishing blue shift of 105 nm is observed for complex 1 when it is measured at 10 K.

A nanoporous chiral metal–organic framework material that exhibits reversible guest adsorption

Assembly of the novel homochiral ligand L(S) (where L(S) is 1,4-benzylidene-bis(S,S)-4-yl-3,5-bis(1-hydroxyethyl)-1,2,4-triazole) and AgNO3 generates a robust, porous, chiral and cationic framework that exhibits reversible guest adsorption.

Di-μ-chlorido-bis(chlorido{2-[(2S)-pyrrolidin-2-yl]-1H-benzimidazole}cadmium(II))

The title binuclear compound, [Cd2Cl4(C11H12N3)2], was synthesized by the hydro­thermal reaction of CdCl2 and the homochiral ligand 2-[(2S)-pyrrolidin-2-yl]-1H-benzimidazole. Each of the two crystallographically independent Cd atoms has a slightly distorted trigonal–bipyramidal geometry and is coordinated by two N atoms from the organic ligand, and by one terminal and two bridging Cl− anions. The crystal structure involves intermolecular N—H⋯Cl hydrogen bonds. One C atom of a pyrrolidine ring is disordered over two positions; the site occupany factors are ca 0.8 and 0.2.

Stereochemical Control of Chirally Flexible Phosphepines

AbstractThe barriers to interconversion of the two enantiomeric atropisomers of 6‐methoxy‐6,7‐dihydro‐5H‐dibenzo[c,e]phosphepine and that of the diastereomeric forms of 6‐(–)‐menthoxy‐6,7‐dihydro‐3H‐dibenzo[c,e]phosphepine were determined by NMR spectroscopical methods to be 19.3 and 18.5 kcal mol–1, respectively, at 298 K. The ratio of the atropisomers was shown to depend on the group bound to phosphorus. Only complexes with two homochiral ligands bound to the each metal center were obtained upon reaction with [Rh(COD)2]+ BF4–. The Rh complexes catalyzed the hydrogenation of α‐acetamidocinnamate. The major isomer of6‐(–)‐menthoxy‐6,7‐dihydro‐5H‐dibenzo[c,e]phosphepinewas found to exhibit higher activity but to afford a product with lower ee than its diastereomer. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Chiral heterocyclic ligands. XIV. Control of directionality in silver coordination polymers through ligand design

Four C(2)-symmetric homochiral ligands derived from (+)-camphor are shown to produce linear chain and ladder silver coordination polymers wherein the directionality and polarisation can be controlled by subtle differences in ligand design.

Triangulo-μ 3-sulfido-trinickel(II) cone-shaped clusters and anion traps: structural characterization

Trinuclear Ni 3S 4N 3 clusters were obtained from (1 S,2 S)-1-monothiasulfato-1-phenyl-2-(methylammoniumyl)propane (tpmp). Three homochiral ligand molecules together with three Ni II ions give rise to a cone-shaped cluster topped by a μ 3-sulfide ion. Each Ni II is in a distorted planar geometry. X-ray structural studies showed that in three cases the three phenyl groups form the rim of a cage which contains R-OSO 3 (R=C 2H 5, C 3H 7) or nitrate anions. The alkyl sulfates were generated during the synthesis reaction, and are hydrogen-bonded through the oxygen atoms to the amine nitrogen atoms. The corresponding compound with the methyl sulfate anion (MeOSO 3) reacts with Fe III nitrate to form a similar compound in which the nitrate anion occupies the cavity and its crystals were analyzed by X-ray diffraction.

IAN Amines: Chiral C2-Symmetric Zirconium(IV) Complexes from Readily Modified Axially Chiral C1-Symmetric β-Diketimines

A general synthesis of β-diketimines derived from Isoquinoline and AminoNaphthalene components (IAN amines) is reported. Beginning from inexpensive 2-naphthol and isoquinoline, the sequence of reactions leading to R-IAN amines is convergent, short, and high-yielding. Several new derivatives are reported (e.g., R = Bn, iPr, tBu, Ph, 2,6-Me2Ph, 2,6-iPr2Ph, 2-Np). All of these were complexed to zirconium(IV) by transamination with Zr(NMe2)4, and in all cases 1:1 R-IAN:Zr complexes immediately formed at 25 °C. Except in cases of severe steric hindrance (iPr-IAN and 2,6-Me2Ph), the corresponding 2:1 IAN:Zr complexes formed at temperatures ranging from 25 to 100 °C in toluene. A feature conserved among all 2:1 IAN:Zr complexes was a remarkable degree of diastereoselectivity favoring a C2-symmetric bis(β-diketiminate) isomer bearing cis-NMe2 and cis-pyridyl ligands. Although all complexations were performed from rac-IAN, the resulting complexes are composed solely of homochiral ligands. The configurational integ...

Chiral Lithiothiophenes as Non‐Transferable Ligands in Organocuprate Conjugate Addition Reactions.

AbstractFor Abstract see ChemInform Abstract in Full Text.