Catalytic Asymmetric Phase‐Transfer Michael Reaction and Mannich‐Type Reaction of Glycine Schiff Bases with Tartrate‐Derived Diammonium Salts

Catalytic asymmetric Michael and Mannich‐type reactions of glycine Schiff bases with chiral two‐center organocatalysts, tartrate‐derived diammonium salts (TaDiASs), are described. On the basis of conformational studies, optimized TaDiASs with a 2,6‐disubstituted cyclohexane spiroacetal were newly designed. These TaDiASs catalyzed the asymmetric Michael and Mannich‐type reactions of glycine Schiff bases with higher enantioselectivity than previous catalysts. In the Mannich‐type reaction, aromatic N‐Boc‐protected imines (Boc=tert‐butoxycarbonyl) as well as enolizable alkyl imines were applicable. As a synthetic application of the catalytic asymmetric Mannich‐type reaction with the optimized TaDiASs, we developed a catalytic asymmetric total synthesis of (+)‐nemonapride, which is an antipsychotic agent.     

A mixed‐ligand quinazoline‐based Ni(II) Schiff base complex: Synthesis,characterization, crystal structure,antimicrobial investigation and catalytic activity for the synthesis of 2H–indazolo[2,1‐b]phthalazine‐triones

A tridentate Schiff base ligand, (E)‐3‐((2‐hydroxy‐3‐methoxybenzylidene)amino)‐2‐methylquinazolin‐4(3H)‐one [HL], and its mixed‐ligand Ni(II) complex [Ni(L)(imi)], were synthesized and fully characterized using elemental analysis, FT‐IR, UV–Vis and ¹HNMR spectroscopy techniques. The structure of the synthesized ligand and complex was determined with single crystal X‐ray diffraction method. In the complex, a square planner geometry was observed around the Ni(II) central atom coordinated with the donor atoms of the Schiff base ligand and one nitrogen of imidazole group. In addition, the catalytic activity of the complex on the three‐component condensation of hydrazine hydrate with phthalic anhydride and dimedone to obtain 2H–indazolo[2,1‐b]phthalazine‐triones was investigated. Furthermore, in‐vitro antimicrobial studies were performed that indicated the great antibacterial activities of the Ni(II) complex against Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa and Bacillus cereus bacteria.     

Synthesis and Characterization of Metal Complexes of a New Unsymmetrical Tridentate NNS Schiff Base Ligand: X‐ray Crystal Structure Determination of Nickel(II) Complex

A new unsymmetrical tridentate NNS Schiff base ligand, 2‐(2‐nitrophenylthio)‐N‐((pyridine‐2‐yl)methylene)benzenamine (L), and its Mn(II ), Ni(II ), Cu(II ), and Zn(II ) complexes were synthesized. These compounds were characterized by different physicochemical and spectroscopic techniques. The molecular structure of [NiL₂ ](ClO₄ )₂ was determined by single‐crystal X‐ray diffraction. In this complex, two ligands coordinate through azomethine‐N, pyridine‐N, and thioether‐S, forming a mononuclear 6‐coordinate distorted octahedral geometry about a nickel.     

立方烷型2-羟甲基-N-邻羟基苯亚甲基苯胺四核镍配合物的合成与晶体结构

The tetranuclear cubane-like complex, [NiL（EtOH）]4·0.5EtOH （1） with tridentate Schiff base ligand （H2L= 2-Hydroxymethyl-N-salicylideneaniline） has been synthesized and its crystal structure and spectroscopic properties have been studied. The complex consists of a tetranuclear （NiO）4 cubane core, of which four nickel（Ⅱ） ions are bridged by μ3-alkoxide group and each nickel（Ⅱ） ion is coordinated to three μ3-alkoxide oxygen atoms, one imino nitrogen atom and one phenoxide oxygen atom from Schiff base ligand, and further ligated by one EtOH molecule, completing a distorted octahedral geometry.     

Transition metal complexes with thiosemicarbazide‐based ligands. XLIV. Aqua(3‐hydroxy‐5‐hydroxymethyl‐2‐methylpyridine‐4‐carboxaldehyde 3‐­methylisothiosemicarbazone‐κ3O,N1,N4)nitratocopper(II) nitrate

The title complex, [Cu(NO₃)(C₁₀H₁₄N₄O₂S)(H₂O)](NO₃), is the first metal complex with a Schiff base derived from iso­thio­semicarbazide and pyridoxal (pyridoxal is 3‐hydroxy‐5‐­hydroxy­methyl‐2‐methyl­pyridine‐4‐carbox­aldehyde). The Cu^II environment is a square pyramid, the equatorial plane of which is formed by the tridentate ONN‐coordinated iso­thio­semicarbazone and one water mol­ecule, while the nitrate ligand is in the apical position. The existence of numerous strong intermolecular hydrogen bonds, and weak C—H?O and C—H?π interactions, leads to a three‐dimensional supramolecular structure.     

Asymmetric anti‐Selective Michael Reaction of Imidazole‐Modified Ketones with trans‐β‐Nitroalkenes

The successful application of imidazole‐modified ketones in asymmetric anti‐selective Michael reactions with trans‐β‐nitroalkenes is presented by employing a newly developed 3‐bromothiophene‐modified chiral diamine ligand. The corresponding conjugate adduct was submitted to further transformations with Grignard reagents to solve the problem of α‐site selectivity of simple linear ketones. Additionally, the syn‐selective product was obtained by treating the anti‐selective adduct with a simple base. In this way, the site‐specific products for both diastereomers in the asymmetric conjugate addition of simple ketones to nitroalkenes can be obtained.     

Bis{1‐[N‐(2‐methoxy­phenyl)imino­methyl]naphthalen‐2(1H)‐onato‐κ3O,N,O′}zinc(II) ethanol solvate

In the crystal structure of the title compound, [Zn(C₁₈H₁₄NO₂)₂]·C₂H₆O, the Zn atom displays a highly distorted octa­hedral coordination involving the O and N atoms of two mol­ecules of the Schiff base 1‐[N‐(2‐methoxy­phenyl)imino­methyl]naphthalen‐2(1H)‐one, which acts as an O,N,O′‐tridentate ligand. The ethanol mol­ecule is bound to the methoxy group of one ligand mol­ecule via a hydrogen bond.     

Chiral‐Zn(NTf2)2‐Complex‐Catalyzed Diastereo‐ and Enantioselective Direct Conjugate Addition of Arylacetonitriles to Alkylidene Malonates

Chiral N,N′‐dioxide/Zn(NTf₂)₂ complexes were demonstrated to be highly effective in the direct asymmetric conjugate addition of arylacetonitriles to alkylidene malonates under mild conditions. A wide range of substrates were tolerated to afford their corresponding products in moderate‐to‐good yields with high diastereoselectivities (82:18–>99:1 d.r.) and enantioselectivities (81–99 % ee). The reactions performed well, owing to the high Lewis acidity of the metal triflimidate and a ligand‐acceleration effect. The N,N′‐dioxide also benefited the deprotonation process as a Brønsted base. The catalytic reaction could be performed on the gram‐scale with retention of yield, diastereoselectivity, and enantioselectivity. The products that contained functional groups were ready for further manipulation. In addition, a possible catalytic model was proposed to explain the origin of the asymmetric induction.     

Axially Dissymmetric Chiral (R)‐N,W‐Bis(2‐hydroxy‐3,5‐ditert‐butyl‐arylmethyl)‐1, 1′‐binaphthalene‐2,2′‐diamine as Chiral Ligands in the Reaction of Diethylzinc to Aldehydes†

Chiral ligand (A)‐N,N′‐Bis(2‐hydroxy‐3,5‐di‐tert‐butyl‐arylmethyl)‐1,1′‐binaphthalene‐2,2′‐diamine derived from the reduction of Schiff base (R)‐2,2′‐bis (3,5‐di‐tert‐butyl‐2‐hydroxybenzylideneamino)‐1, 1′‐binaphthyl with LiAlH₄, is fairly effective in the asymmetric addition reaction of diethylzinc to aldehydes by which good yields (46%‐94%) of the corresponding sec‐alcohols can be obtained in moderate ee (51%‐79%) with R configuration for a variety of aldehydes.     

Palladacycle Catalyzed Asymmetric PH Addition of Diarylphosphines to N‐Enoyl Phthalimides

The first asymmetric phospha‐Michael addition of diarylphosphines to N‐enoyl phthalimides has been developed in the presence of a chiral palladacycle catalyst. A library of free chiral tertiary phosphine adducts were directly obtained with excellent yields and enantioselectivities. Products can be subsequently functionalized to afford β‐phosphinoamides, the direct preparation of which from cinnamides has been notoriously challenging.     

{4‐[(Carbamimidoylhydrazono)methyl‐κ2N1,N4]‐5‐hydroxymethyl‐2‐methylpyridinium‐3‐olate‐κO}(methanol‐κO)copper(II) dinitrate

The title compound, [Cu(C₉H₁₃N₅O₂)(CH₄O)](NO₃)₂, consists of square‐planar cationic complex units where the Cu^II centre is coordinated by an N,N′,O‐tridentate pyridoxal–aminoguanidine Schiff base adduct and a methanol molecule. The tridentate ligand is a zwitterion exhibiting an almost planar conformation. The dihedral angles between the mean planes of the pyridoxal ring and the six‐ and five‐membered chelate rings are all less than 2.0°. The charge on the complex cation is neutralized by two nitrate counter‐ions. Extensive N—H...O and C—H...O hydrogen bonding connects these ionic species and leads to the formation of layers. The pyridoxal hydroxy groups are the only fragments that deviate significantly from the flat layer structure; these groups are involved in O—H...O hydrogen bonding, connecting the layers into a three‐dimensional crystal structure.     

Promotion of Henry reactions using Cu(OTf)2 and a sterically hindered Schiff base: access to enantioenriched β-hydroxynitroalkanes

The steric and electronic properties of chiral Schiff base ligands derived from cinchona alkaloids were evaluated in asymmetric Henry reactions. Amongst these, the sterically hindered ligand 2 showed outstanding catalytic efficiency in the Cu(II) catalyzed asymmetric addition of nitroalkanes to a variety of aldehydes to afford the desired adducts in high yields (up to 97%) with excellent enantioselectivities (up to 99% ee) and moderate to good diastereoselectivities (up to 84:16 dr).     

Carboxylate ion dependency in the Cu(II) catalysed asymmetric Henry reaction: Structural characterisation of a tridentate Schiff base complex containing a coordinated carboxylic acid

Six tridentate Schiff base ligands containing tertiary butyl or benzyl substituents were prepared from chiral amino alcohols and salicylaldehyde derivatives. The ligands were employed as catalysts for the Cu(II) catalysed asymmetric Henry reaction. It was discovered that when different carboxylate salts were used instead of copper acetate as the Cu(II) salt, significant changes in the enantioselectivity of the reactions were observed. Addition of Cu(OAc)₂ to the ligand prepared from salicylaldehyde and α,α‐diphenyl‐tert ‐leucinol resulted in the formation of dark green crystals. X‐ray structural analysis of these crystals showed that a square planar monomeric complex had been formed rather than the expected dimer. In the structure, the copper(II) centre is bonded to the tridentate ONO ligand and an acetate ion. There is a strong hydrogen bond between the protonated alcoholic oxygen of the Schiff base ligand and the uncoordinated acetate oxygen atom. These results, taken together, indicate that the carboxylate anion may be an important part of the active intermediate when this type of copper complex is used as a catalyst in the asymmetric Henry reaction.     

Diphenylprolinol Silyl Ether Catalyzed Asymmetric Michael Reaction of Nitroalkanes and β,β‐Disubstituted α,β‐Unsaturated Aldehydes for the Construction of All‐Carbon Quaternary Stereogenic Centers

The asymmetric Michael reaction of nitroalkanes and β,β‐disubstituted α,β‐unsaturated aldehydes was catalyzed by diphenylprolinol silyl ether to afford 1,4‐addition products with an all‐carbon quaternary stereogenic center with excellent enantioselectivity. The reaction is general for β‐substituents such as β‐aryl and β‐alkyl groups, and both nitromethane and nitroethane can be employed. The addition of nitroethane is considered a synthetic equivalent of the asymmetric Michael reaction of ethyl and acetyl substituents by means of radical denitration and Nef reaction, respectively. The short asymmetric synthesis of (S)‐ethosuximide with a quaternary carbon center was accomplished by using the present asymmetric Michael reaction as the key step. The reaction mechanism that involves the E/Z isomerization of α,β‐unsaturated aldehydes, the retro‐Michael reaction, and the different reactivity between nitromethane and nitroethane is discussed.     

2,6‐Bis(1‐benzyl‐1H‐1,2,3‐triazol‐4‐yl)pyridine and its octahedral copper complex

In the tridentate ligand 2,6‐bis(1‐benzyl‐1H‐1,2,3‐triazol‐4‐yl)pyridine, C₂₃H₁₉N₇, both sets of triazole N atoms are anti with respect to the pyridine N atom, while in the copper complex aqua[2,6‐bis(1‐benzyl‐1H‐1,2,3‐triazol‐4‐yl)pyridine](pyridine)(tetrafluoroborato)copper(II) tetrafluoroborate, [Cu(BF₄)(C₅H₅N)(C₂₃H₁₉N₇)(H₂O)]BF₄, the triazole N atoms are in the syn–syn conformation. The coordination of the Cu^II atom is distorted octahedral. The ligand structure is stabilized through intermolecular C—H...N interactions, while the crystal structure of the Cu complex is stabilized through water‐ and BF₄‐mediated hydrogen bonds. Photoluminiscence studies of the ligand and complex show that the ligand is fluorescent due to triazole–pyridine conjugation, but that the fluorescence is quenched on complexation.     

Di‐μ‐aqua‐bis­[(N‐salicyl­idene‐β‐alaninato‐κ3O,N,O′)copper(II)] urea disolvate

Crystals of the title compound, [Cu₂(C₁₀H₉NO₃)₂(H₂O)₂]·2CH₄N₂O, consist of two (N‐salicyl­idene‐β‐alaninato‐κ³O,N,O′)copper(II) coordination units bridged by two water moieties to form a dimer residing on a crystallographic inversion center, along with two uncoordinated urea mol­ecules. The Cu^II atom has square‐pyramidal coordination, with three donor atoms of the tridentate Schiff base and an O atom of the bridging aqua ligand in the basal plane. The axial position is occupied by the second bridging water ligand at a distance of 2.5941 (18) Å. Hydro­gen bonds between mol­ecules of urea and the neighboring dimer units lead to the formation of a two‐dimensional grid of mol­ecules parallel to [101]. The superposition of the normals of the pyramidal base planes in the direction [100] indicates possible π–π interactions between the neighboring units.     

Six‐coordinated vanadium(IV) complexes with tridentate task‐specific ionic liquid Schiff base ligands: Synthesis,characterization and effect of ionic nature on catalytic activity

By reaction of 5‐(chloromethyl)salicylaldehyde with triphenylphosphine and N‐methylimidazole in two separate reactions, salicylaldehydetriphenylphosphonium chloride (S²) and salicylaldehydemethylimidazolinium chloride (S³) were prepared. Reaction of 2‐(aminomethyl)pyridine with these aldehydes resulted in the task‐specific ionic liquid Schiff base ligands L¹ and L², respectively. Then six‐coordinated vanadium(IV) Schiff base complexes of VO(acac)L^1–4 were synthesized by reactions of these tridentate Schiff base ligands and VO(acac)₂ in 1:1 stoichiometry. The aldehydes, ligands and VO(acac)L^1–4 complexes were characterized using infrared, ¹H NMR, ¹³C NMR, ³¹P NMR, UV–visible and mass spectroscopies, as well as elemental analysis. Paramagnetic property of the complexes was also studied using magnetic susceptibility measurements. The complexes were used as catalysts in epoxidation of cyclooctene and oxidation of methylphenyl sulfide and the reaction parameters were optimized. The effect of the ionic nature of the complexes was investigated in these oxidation reactions. The catalytic activity of the complexes could be varied by changing the ionic (cationic or anionic) character of VO(acac)L^1–4 catalysts in which counter anion variation showed a greater effect than cationic moiety variation.     

π–π Dimerization of a mono(pyridyl–imine) platinum(II) chelate

The cation of the title complex salt, chlorido{2,2‐dimethyl‐N‐[(E)‐1‐(pyridin‐2‐yl)ethylidene]propane‐1,3‐diamine}platinum(II) tetrafluoridoborate, [PtCl(C₁₂H₁₉N₃)]BF₄, exhibits a nominally square‐planar Pt^II ion coordinated to a chloride ion [Pt—Cl = 2.3046 (9) Å] and three unique N‐atom types, viz. pyridine, imine and amine, of the tridentate Schiff base ligand formed by the 1:1 condensation of 1‐(pyridin‐2‐yl)ethanone and 2,2‐dimethylpropane‐1,3‐diamine. The cations are π‐stacked in inversion‐related pairs (dimers), with a mean plane separation of 3.426 Å, an intradimer Pt...Pt separation of 5.0785 (6) Å and a lateral shift of 3.676 Å. The centroid (Cg) of the pyridine ring is positioned approximately over the Pt^II ion of the neighbouring cation (Pt...Cg = 3.503 Å).     

Helicity Induction and Its Static Memory of Poly(biphenylylacetylene)s Bearing Pyridine N‐Oxide Groups and Their Use as Asymmetric Organocatalysts

Novel poly(biphenylylacetylene) derivatives carrying different types of pyridine N‐oxide units with a bulky or less‐bulky substituent at a different position as the functional pendant groups (poly‐ 2a and poly‐ 2b ) were synthesized by the rhodium‐catalyzed polymerization of the corresponding monomers. The influence of the steric environment around the catalytically active pyridine N‐oxide sites on the helicity induction and its static memory as well as the asymmetric catalytic activities of the resulting helical polymers with a macromolecular helicity memory was investigated. The polyacetylenes formed an excess one‐handed helical conformation upon noncovalent interactions with optically active alcohols and the induced macromolecular helicities of the polyacetylenes were efficiently memorized after the removal of the chiral inducers. Poly‐ 2b with the macromolecular helicity memory showed an enantioselectivity for the catalytic asymmetric allylation of benzaldehydes, producing optically active allyl alcohols, although their enantioselectivities were low. On the other hand, poly‐ 2a exhibited a negligible catalytic activity probably due to the bulky substituent at the o‐position of the pyridine N‐oxide residues, while poly‐ 2a underwent a unique helix‐inversion with the increasing concentration of chiral alcohols and the opposite helicity of poly‐ 2a was further successfully memorized. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 2481–2490     

Asymmetric structure of cis‐[N‐(9‐anthracenylmethyl)‐1,2‐ethanediamine]dipyridineplatinum(II) dinitrate

Platinum antitumour agents, containing aromatic rings, which are used for targeting DNA in effective therapies for the treatment of cancer. We have synthesized the title metallocomplex with an aromatic ligand and determined its crystal structure. In many cases, complexes of platinum and other metals have a symmetrical structure. In contrast, the platinum(II) complex with pyridine and N‐(9‐anthracenylmethyl)‐1,2‐ethanediamine as ligands (systematic name: cis‐{N‐[(anthracen‐9‐yl)methyl]ethane‐1,2‐diamine‐κ²N ,N ′}bis(pyridine‐κN )platinum(II) dinitrate), [Pt(C₅H₅N)₂(C₁₇H₁₈N₂)](NO₃)₂, is asymmetric. Of the two pyridine ligands, only one is π‐stacked with anthracene, resulting in an asymmetric structure. Moreover, the angle of orientation of each pyridine ligand is variable. Further examination of the packing motif confirms an intermolecular edge‐to‐face interaction.