M8L12 cubic cages (M = MnII, ZnII or CdII), with all eight metal ions having all facial Δ or facial Λ configurations and having an encapsulated anion, were prepared by the self-assembly of m-xylene-bridged imidazolyl-imine ligands and MX2 (X = PF6−, SbF6−, TfO−) salts; the encapsulated anion exchange with different anions (SbF6−, Tf2N−, NO3−, TsO−) was studied and the results with NO3− and TsO− indicate that anions on the cage surfaces affect the encapsulated anion exchange and the occupancy of the cage.

The pyridine-containing ligands L1 and L2 react with Ni2+ ions to afford dinuclear triple-stranded helicate and tetrahedral cage supramolecular complexes, respectively; the two architectures exhibit contrasting reactivity towards electro- and photocatalytic proton reduction.

A series of chiral polyphenyl-bridged bis(2,2′-bipyridine) ligands comprising one to four phenyl units were synthesized. The ligands give a weak signal in the CD spectra, but upon addition of tetrachloroferric acid or perchloric acid, a more intense CD signal is observed for ligands having two or more phenyl units. Titration experiments show that the CD signal comes from a monoprotonated species which gives broadened and upfield shifted 1H NMR signals. Variable temperature NMR experiments split the broadened signals into two sets of signals when the temperature is decreased. One of the sets is remarkably upfield while the other has chemical shifts similar to those of the free ligand. The X-ray crystal structures of a free ligand (mono phenyl), a monoprotonated ligand (biphenyl) and a biprotonated ligand (tetraphenyl) were obtained and the structure of the monoprotonated ligand shows that it is a double-stranded helix, which is stabilized by interior hydrogen bonding between the pyridinium N–H and the pyridine N of another ligand strand, and exterior CH⋯Cl hydrogen bonding between FeCl4− and the two ligand strands. Theoretical DFT calculations show that there is such stabilization in solution as well. With the perchlorate anion, the helix formation process is reversible with Et3N which accompanies an on/off CD signal change.

With a series of chiral pyridine-based tetradentate pyridyl-thiazole ligands L, three types of binuclear helical metal complexes were synthesized. They were the Re(I) single-stranded complexes of formula [Re2(L)(CO)6Br2], the Ag(I) double-stranded complexes of formula [Ag2(L)2](ClO4)2 and the Cu(II) triple-stranded complex of formula [Cu2(L)3](ClO4)4. Each type of them has been characterized using CD spectroscopy and if possible 1H NMR spectroscopy. Three single crystal structures, one from each type, have been determined.Graphical abstractWith a series of chiral pyridine-based tetradentate pyridyl-thiazole ligands L, three types of binuclear helical metal complexes were synthesized. The structures of these helicates were characterized with CD spectroscopy and X-ray crystallography.

Dodecanuclear hexagonal-prismatic M12L18 cages were prepared by a subcomponent self-assembly process with commercially available pyridinecarboxaldehyde, m-xylenediamine, and cadmium(II) perchlorate or manganese(II) perchlorate. The NMR spectrum of the Cd cage shows that there are three independent ligand sets, and the X-ray crystal structure of the Mn cage reveals that the structure has both fac-Δ- and mer-Λ-configured metal centers in a 1:1 ratio. The cage structure also has a large cavity that contains five perchlorate anions.

A ΛΛΛΛ-M4L6 tetrahedral manganese cage with a captured perchlorate or trifluoromethanesulfonate anion was synthesized using a chiral quaterpyridine; the captured anion is exchangeable and the removal of the captured ClO4− from the cage was studied by theoretical calculation.A ΛΛΛΛ-M4L6 tetrahedral manganese cage with a captured perchlorate or trifluoromethanesulfonate anion was synthesized using a chiral quaterpyridine.Highlights► Stereoselective formation of new ΛΛΛΛ-M4L6 tetrahedral manganese cage ► Study on anions capture and exchange by CD and ESI-MS ► Information of anions exchange pathway from studying the anions exchange rate and theoretical calculation on captured anion departure

Self assembly of phenyl bridged bisbipyridines with manganese perchlorate gave structurally different metallo-macrocycles having cis-labile coordination sites which can catalyse olefin epoxidation with peracetic acid in good yield.

Two new chiral pyridyl pyrazine ligands reacted with silver(I) ion to form two different polymers—one with an achiral trigonal bipyramidal silver(I) chain and the other a chiral tetrahedral chain with an interesting repeating Λ,Δ-silver(I) configuration.Research Highlights► Two new chiral silver coordination polymers based on chiral pyridyl pyrazine ligands. ► One polymer is a directional linear polymer. ► Another polymer has a non-directional zigzag form with a repeating Λ,Δ-configuration. ► Circular dichroism spectra of the two polymers are compared.

New binuclear double-stranded helicates were formed between manganese(II) perchlorate and chiral phenyl- and polyphenyl-bridged oligopyridines; they are active catalysts for alkene epoxidation.

Reaction of a pinene-based pyridylthioamide with 1,4-dibromo-2,3-butanedione in refluxing methanol yielded a new chiral pyridylthiazole ligand L which forms a dinuclear double-stranded helicate with Cu(I) ions; this helicate has opposite helical chirality when compared with its quaterpyridine analogue.

A series of single-stranded helical Re(I) complexes, of formula [Re2(L)Br2(CO)6], were prepared by reacting [Re(CO)5Br] with chiral quaterpyridines L1−4. By 1H and 13C NMR analysis, all the crude complexes consisted of a pair of stereoisomers. Sterically more demanding ligand L4 induced a higher ratio (80:20) than L1−3 (about 56:44). Stereochemically pure complexes could be obtained by recrystallization in CH2Cl2. X-ray crystallographic analysis of single crystals from purified complexes showed a single-stranded helical structure with a bridging ligand wrapped around two distorted octahedral rhenium metals, both of which possessed one bromide ligand and three carbonyl ligands in a fac coordination. The helical core is established by extensive noncovalent electrostatic interactions and chiral information is transmitted from the ligand to the helix through these interactions. Solution behavior was studied by CD spectroscopy, and the strong Cotton effect confirms the integrity of the helical structure in solution. The diastereoselectivity of helicates is proposed to be induced by steric interaction between the bromine atom and the substituent of the bridging ligand.

Optically pure C1- and C2-terpyridine ligands (L) form cobalt(II) and iron(II) complexes of formula [Co(L)Cl2] and [Fe(L)Cl2], respectively, and Iron(III) complexes of formulas [Fe(L)Cl3]. Structures of three new chiral cobalt(II) and one iron(III) complexes were analysed using X-ray crystal structure analysis. These complexes were shown to be precursor of efficient catalyst for cyclopropanation. Reaction with AgOTf converted the complex to active catalyst, which gave enantioselectivities of up to 76% ee for the trans-isomers and 83% ee for the cis-isomers of styrene cyclopropanes with ethyl diazoacetate. Hammett studies showed the active species for both cobalt and iron complexes to have a non-linear relationship to σp constant.Optically pure C1- and C2-terpyridine ligands (L) form cobalt(II) and iron(II) complexes of formula [Co(L)Cl2] and [Fe(L)Cl2], respectively, and iron(III) complexes of formulas [Fe(L)Cl3]. These complexes were shown to be precursors of efficient catalysts for cyclopropanation, which gave enantioselectivities of up to 76% ee for the trans-isomers and 83% ee for the cis-isomers of styrene cyclopropanes with ethyl diazoacetate.

A new fluorescence macrocyclic receptor based on the Zn(II) complex of a C2-terpyridine and a crown ether has been developed for molecular recognition of zwitterionic amino acids in water/DMF solution with remarkable selectivity towards l-aspartate (K = 4.5 × 104 M−1) and l-cysteine (K = 2.5 × 104 M−1).A new fluorescence macrocyclic receptor based on the Zn(II) complex of a C2-terpyridine and a crown ether has been developed for molecular recognition of zwitterionic amino acids in water/DMF solution.

A chiral iron-sexipyridine complex–hydrogen peroxide mixture is a highly efficient catalytic system for styrene epoxidation with excellent reactivity (3 min, 95% yield) and chemoselectivity (98%).

A high-efficiency nondoped green organic light-emitting device was demonstrated by using a novel electroluminescent material 3,6-di[8-(7,10-diphenylfluoranthenyl)] phenyl-9-[8-(7,10-diphenylfluoranthenyl)] phenylcarbazole (TDPFPC) as an efficient electrofluorescence emitter. The device with a simple structure of ITO/α-napthylphenylbiphenyl diamine/TDPFPC/4,7-diphenyl-1,10-phenanthroline/LiF/Al exhibited green emission with Commission Internationale de L’Eclairage coordinates of (0.25, 0.49), a high current efficiency of 10.1 cd/A, and a high power efficiency of 12.1 lm/W.A high-efficiency nondoped green organic light-emitting device of ITO/NPB/TDPFPC/BPhen/LiF/Al was demonstrated by using a novel electroluminescent material TDPFPC.

In this article, an overview of the investigations on chiral py-containing ligands in asymmetric catalysis that have carrried out in the past years is provided. The ligands are divided into different types based on the number of pyridine moieties present and the way they are connected in the ligands, namely monopyridine, dipyridine (two pyridines connected by a bridge), bipyridine, phen(1,10-phenanthroline), terpyridine and oligopyridine. In each section, the synthetic strategies for each type of ligands are discussed and representative examples are given. Selected important results in asymmetric catalysis are mentioned.

This paper reports the synthesis of a new starburst molecule, 4,4′,4′′-tris[(2,3,4,5-tetraphenyl)phenyl]phenylamine (TTPPPA) and its application as a hole-transporting material in organic light-emitting devices (OLEDs). Although TTPPPA has almost the same ionization potential as 1,4-bis(1-naphthylphenylamino)biphenyl (NPB), the TTPPPA-based device of ITO/TTPPPA/Alq3/LiF/Al yields much better efficiency of 5.3 cd/A and 4.3 lm/W than the standard ITO/NPB/Alq3/LiF/Al device (3.0 cd/A and 2.9 lm/W). The remarkable performance enhancement is attributed to a better balance of hole and electron injection in the TTPPPA-based device. Further, TTPPPA has a much higher glass-transition temperature (Tg, 202 °C) than NPB (Tg, 98 °C), suggesting that TTPPPA can be an alternative material to NPB especially for high-temperature applications of OLEDs and other organic electronic devices.

Chiral double-stranded helicates, formed between Cu(I) ion and C2-symmetric oligopyridines, were used for catalytic asymmetric cyclopropanation of alkenes; low catalyst loadings (0.2 mol%), high TONs (up to 404) and short reaction times (30–60 min) were achieved with [Cu2L2]OTf2 (L = chiral C2-symmetric terpyridine).

Re(I) tricarbonyl bipyridine and terpyridine complexes catalyse stereospecific cyclopropanation of alkenes; high selectivity of cyclopropane vs coupling and an ee of 73% and 62% for cis- and trans-cyclopropanes of styrene respectively were achieved with the [Re(L)(CO)3(MeCN)]OTf complex (L = chiral C2-symmetric terpyridine ligand).

Chiral C2-symmetric quaterpyridine L reacts with [Pd(η3-C3H5)Cl]2 to form a chiral single-stranded helical binuclear palladium complex of formula [Pd2(η3-C3H5)2(L)]2+; the complex can efficiently catalyze allylic substitution of 1,3-diphenylprop-2-enyl acetate with dimethyl malonate with enantioselectivity up to 85%.

Terpyridine macrocycle 1 is shown to be a strong chelating agent for organic ammonium salts and also a useful chromophore in fluorescent sensing. It exhibits very good enantioselectivity (Kobs (S)/Kobs (R) = 3.8) in chiral discrimination of α-phenylglycine methyl ester hydrochloride (PhEtOMe).

The first series of chiral 2,2′:6′,2″-terpyridine tri-N-oxide ligands have been developed; They were showed to be active Lewis base-catalysts for asymmetric allylation of aldehydes using allyltrichlorosilane with optimal results at 0 °C for electron-deficient aromatic aldehydes (yields up to 97% and enantioselectivities up to 86% ee).

Chiral N,O pyridine alcohols HL1–HL6 were used to form complexes with copper(II) ions. Ligands HL1 and HL2 formed complexes with copper(II) ions when Cu(OAc)2 and HL were refluxed in methanol/ethanol mixture. Ligand HL3 formed a complex with copper(II) when deprotonated with NaH and stirred in a Cu(II) acetate THF solution. Ligands HL4–HL6 did not form complexes with copper(II) under similar conditions. Two complexes, [Cu(L1)2] and [Cu(L2)2], were isolated as single crystals and characterized by X-ray crystallography. These complexes showed low catalytic activities in asymmetric reactions. However, they became active when reacted with triflic acid. Copper complexes, [Cu(L)] or [Cu(L)]+, formed in situ by reacting ligands HL with copper(I) or (II) ions, respectively, were also found to be active copper catalysts for asymmetric cyclopropanation of styrene with ethyl diazoacetate and allylic oxidation of cyclohexene with t-butylperoxybenzoate. Enantioselectivities up to 56% and 38% were obtained in asymmetric cyclopropanation of styrene and asymmetric allylic oxidation of cyclohexene, respectively.Chiral N,O pyridine alcohols HL were used to form complexes with copper(II) ions. Three complexes, with formula [Cu(L)2], were isolated. Two crystal structures are described. Copper complexes formed in situ were found to be active catalysts for asymmetric catalysis.

Iodo-(5,10,15,20-tetrakis(1,2,3,4,5,6,7,8-octahydro-1,4:5,8-dimethanoanthracen-9-yl)porphyrinatorhodium(III), designated as [Rh(P*)(I)], was prepared and its catalytic activity in the asymmetric cyclopropanation of alkenes with ethyl diazoacetate (EDA) was examined. High catalyst turnovers (TON >103) and moderate enantioselectivities (up to 68% ee) were observed. However, the obtained trans/cis ratios are low. Competition experiments revealed that electron-donating substituents on styrene accelerate the cyclopropanations. The log(kX/kH) versus σ+ plot for substituted styrenes exhibits a good linearity with a small negative ρ+ value (−0.14). [Rh(P*)(I)] is also active in the intramolecular cyclopropanation of allyl diazoacetates. A comparison between rhodium and ruthenium porphyrin complexes was made.Graphic

New families of chiral terpyridine mono-N-oxides L1–L3 and di-N-oxides L4–L6, were synthesized in moderate to good yields by simple oxidation of their corresponding terpyridines with m-CPBA. The copper(II) triflate complexes of these ligands were found to be highly effective catalysts for asymmetric cyclopropanation of styrene with ethyl diazoacetate. The isolated yields of cyclopropane were excellent and the enantiomeric excesses of up to 83% were observed. Competition experiments with substituted styrenes showed good σ+ correlations with ρ=−0.70 for mono-N-oxide L3 and ρ=−0.69 for di-N-oxide L6.Copper(II) triflate complexes of the mono- and di-N-oxide ligands induced ee of up to 83% with excellent yields in the Cu(II)-catalyzed cyclopropanation of a number of styrene derivatives.2-(1-N-Oxide-7,7-dimethyl-5,6,7,8-tetrahydro-6,8-methanoquinolin-2-yl)-6-(7,7-dimethyl-5,6,7,8-tetrahydro-6,8-methanoquinolin-2-yl)pyridineC29H31N3O[α]D=−29.6 (c 0.45, CHCl3)Source of chirality: (1R)-(+)-nopinoneAbsolute configuration: 6R,8R2-(1-N-Oxide-8,9,9-trimethyl-5,6,7,8-tetrahydro-5,8-methanoquinolin-2-yl)-6-(8,9,9-trimethyl-5,6,7,8-tetrahydro-5,8-methanoquinolin-2-yl)pyridineC31H35N3O[α]D=−50.4 (c 0.5, CHCl3)Source of chirality: (1R)-(+)-camphorAbsolute configuration: 5S,8R2-(1-N-Oxide-8,9,9-trimethyl-5,6,7,8-tetrahydro-5,8-methanoquinolin-2-yl)-6-(8,9,9-trimethyl-5,6,7,8-tetrahydro-5,8-methanoquinolin-2-yl)pyridineC31H35N3O[α]D=−17.8 (c 0.5, CHCl3)Source of chirality: (1R)-(+)-camphorAbsolute configuration: 5S,8R2-(1-N-Oxide-6,6,8-trimethyl-5,6,7,8-tetrahydro-5,7-methanoquinolin-2-yl)-6-(6,6,8-trimethyl-5,6,7,8-tetrahydro-5,7-methanoquinolin-2-yl)pyridineC31H35N3O[α]D=−1089.9 (c 0.5, CHCl3)Source of chirality: (R)-(−)-isopinocamphenolAbsolute configuration: 5R,7R,8S2,6-Bis(1-N-oxide-7,7-dimethyl-5,6,7,8-tetrahydro-6,8-methanoquinolin-2-yl)pyridineC29H31N3O2[α]D=−214.2 (c 0.5, CHCl3)Source of chirality: (1R)-(+)-nopinoneAbsolute configuration: 6R,8R2,6-Bis(1-N-oxide-6,6,8-trimethyl-5,6,7,8-tetrahydro-5,7-methanoquinolin-2-yl)pyridineC31H35N3O2[α]D=−74.7 (c 0.5, CHCl3)Source of chirality: (R)-(−)-isopinocamphenolAbsolute configuration: 5R,7R,8S

Chiral copper(I)–bipyridine complexes were prepared and used as catalysts in the enantioselective allylic oxidation of cyclic alkenes with tert-butyl perbenzoate. The yields ranged from moderate to good and enantioselectivities up to 70% were observed.Chiral copper(I)–bipyridine complexes were prepared and used as catalysts in the enantioselective allylic oxidation of cyclic alkenes with tert-butyl perbenzoate. The yields ranged from moderate to good and enantioselectivities up to 70% were observed.6-[2-Hydroxy-1,3,3-trimethylbicyclo[2.2.1]hept-2-yl]-2,2′-bipyridineC20H24N2O[α]D25=−60.0 (c 0.52, CCl4)Source of chirality: (1R)-(−)-fenchoneAbsolute configuration: (1R,2R)6-(2-Hydroxy-6,6-dimethylbicyclo[3.1.1]hept-2-yl)-2,2′-bipyridineC19H22N2O[α]D25=−19.4 (c 0.51, CCl4)Source of chirality: (1R)-(+)-nopinoneAbsolute configuration: (1R,2R)2-[2-Hydroxy-1,3,3-trimethylbicyclo[2.2.1]hept-2-yl]-6-phenylpyridineC21H24NO[α]D25=−71.2 (c 0.51, CCl4)Source of chirality: (1R)-(−)-fenchoneAbsolute configuration: (1R,2R)2-(2-Hydroxy-6,6-dimethylbicyclo[3.1.1]hept-2-yl)-6-phenylpyridineC20H23NO[α]D25=−35.4 (c 0.52, CCl4)Source of chirality: (1R)-(+)-nopinoneAbsolute configuration: (1R,2R)

A number of chiral C2-symmetric 2,2′:6′,2″ terpyridines L1–L4 were synthesized in moderate to good yields from commercially available chiral materials. Copper(II) and rhodium(III) chloride complexes of these ligands were prepared in good yields. The Rh(L2)Cl3 complex was isolated as a yellow crystalline solid and characterized by X-ray crystallography. Both Cu(L)(OTf)2 and Rh(L)(OTf)3 were found to be active catalysts in the cyclopropanation of styrene with ethyl diazoacetate. Enantioselectivity up to 82% e.e. was observed.Graphic2,6-Bis(7,7-dimethyl-5,6,7,8-tetrahydro-6,8-methanoquinolin-2-yl)pyridineC29H31N3[α]D25=−49.4 (c=0.50, CH2Cl2)Source of chirality: (1R)-(+)-nopinoneAbsolute configuration: 6R,8R2,6-Bis(8,9,9-trimethyl-5,6,7,8-tetrahydro-5,8-methanoquinolin-2-yl)pyridineC31H35N3[α]D25=−15.8 (c=0.53, CH2Cl2)Source of chirality: (1R)-(+)-camphorAbsolute configuration: 5S,8R2,6-Bis(5-methyl-8-isopropyl-5,6,7,8-tetrahydroquinolin-2-yl)pyridineC31H39N3[α]D25=−58.8 (c=0.50, CH2Cl2), mp 155–158°CSource of chirality: (−)-menthoneAbsolute configuration: 5R,8R2,6-Bis(5-methyl-8-isopropyl-5,6,7,8-octahydroquinolin-2-yl)-pyridineC31H39N3[α]D25=−49.0 (c=0.53, CH2Cl2), mp 124–125°CSource of chirality: (−)-menthoneAbsolute configuration: 5R,5′R,8R,8′S

New C2-symmetric chiral 2,2′:6′,2′′-terpyridines were prepared from readily available homochiral materials. Copper complexes of these ligands were prepared in situ and their catalytic activities in cyclopropanations of alkenes with alkyl diazoacetate to give cyclopropyl esters were studied. In all cases, the cyclopropyl ester yields were excellent and enantioselectivities up to 94% ee were observed. Competition experiments revealed that electron-donating substituents on styrene accelerate the reaction. Hammett plot exhibited a good linearity with negative ρ+ value (−0.79).

M8L12 cubic cages (M = MnII, ZnII or CdII), with all eight metal ions having all facial Δ or facial Λ configurations and having an encapsulated anion, were prepared by the self-assembly of m-xylene-bridged imidazolyl-imine ligands and MX2 (X = PF6−, SbF6−, TfO−) salts; the encapsulated anion exchange with different anions (SbF6−, Tf2N−, NO3−, TsO−) was studied and the results with NO3− and TsO− indicate that anions on the cage surfaces affect the encapsulated anion exchange and the occupancy of the cage.

Chiral double-stranded helicates, formed between Cu(I) ion and C2-symmetric oligopyridines, were used for catalytic asymmetric cyclopropanation of alkenes; low catalyst loadings (0.2 mol%), high TONs (up to 404) and short reaction times (30–60 min) were achieved with [Cu2L2]OTf2 (L = chiral C2-symmetric terpyridine).

The pyridine-containing ligands L1 and L2 react with Ni2+ ions to afford dinuclear triple-stranded helicate and tetrahedral cage supramolecular complexes, respectively; the two architectures exhibit contrasting reactivity towards electro- and photocatalytic proton reduction.

Self assembly of phenyl bridged bisbipyridines with manganese perchlorate gave structurally different metallo-macrocycles having cis-labile coordination sites which can catalyse olefin epoxidation with peracetic acid in good yield.

Re(I) tricarbonyl bipyridine and terpyridine complexes catalyse stereospecific cyclopropanation of alkenes; high selectivity of cyclopropane vs coupling and an ee of 73% and 62% for cis- and trans-cyclopropanes of styrene respectively were achieved with the [Re(L)(CO)3(MeCN)]OTf complex (L = chiral C2-symmetric terpyridine ligand).

New binuclear double-stranded helicates were formed between manganese(II) perchlorate and chiral phenyl- and polyphenyl-bridged oligopyridines; they are active catalysts for alkene epoxidation.

Reaction of a pinene-based pyridylthioamide with 1,4-dibromo-2,3-butanedione in refluxing methanol yielded a new chiral pyridylthiazole ligand L which forms a dinuclear double-stranded helicate with Cu(I) ions; this helicate has opposite helical chirality when compared with its quaterpyridine analogue.

A chiral iron-sexipyridine complex–hydrogen peroxide mixture is a highly efficient catalytic system for styrene epoxidation with excellent reactivity (3 min, 95% yield) and chemoselectivity (98%).