Coordination chemistry and biological activity of bidentate and quadridentate nitrogen–sulfur donor ligands and their complexes

The ligand S-benzyldithiocarbazate (SBDTC) acts as a bidentate sulfur–nitrogen chelating agent. The reaction of Sn^II or Sb^III with SBDTC under alkaline conditions gives complexes of composition [Sn(SBDTCA)₂] · 2H₂O and [Sb(SBDTCA)Cl₂ · 2H₂O]. A quadridentate Schiff base of SBDTC with benzil, having a donor sequence SNNS, yields complexes, [Cd(SNNS)] and [Zr(O)(SNNS) · H₂O]. The ligands and the complexes have been characterized by elemental analyses, i.r., u.v.–vis., molar conductance measurements and ¹H-n.m.r. spectroscopy. SBDTC, Sn^II and Sb^III complexes and the SNNS Schiff base together with its Cd^II and Zr^IV complexes display significant antifungal, antibacterial and anti-cancer activity. The Sn^II complex and the SNNS free Schiff base were very effective against Melanoma (skin cancer cells). The SBDTC and its Sn^II complex were also very effective against Renal carcinoma (kidney cancer cells). The results have been compared with those of the uncomplexed metal salts and the free ligands. The minimum concentrations for the evaluation of the above activities for CD₅₀ of the samples were in the 1.0–15 g cm^–3 range.     

Construction of C1-symmetric zirconium complexes by the design of new Salan ligands. Coordination chemistry and preliminary polymerisation catalysis studies

The first synthesis of achiral and chiral [ONNO']-type Salan ligands featuring two different phenol arms, and the diastereoselective formation of the corresponding octahedral C1-symmetric zirconium complexes is described; the activity and isospecificity induction of the [ONNO']Zr(bn)2 complexes in 1-hexene polymerisation reflected those of the parent symmetric compounds.     

Synthesis of novel chiral N, P-containing multidentate ligands and their applications in asymmetric transfer hydrogenation

Novel chiral PN₄-type multidentate aminophosphine ligands have been successfully synthesized by Schiff-base condensation of bis（o-formylphenyl）phenylphosphane and various chiral amino-sulfonamides.Their structures were fully characterized by IR,EI-MS and NMR.The catalytic systems,prepared in situ from the multidentate ligands and iridium（I） complexes,showed high activity in asymmetric transfer hydrogenation of propiophenone in 2-propanol solution,leading to corresponding optical alcohol with up to 75%ee.     

Enantiopure inherently chiral calix[4]arene derivatives containing quinolin-2-yl-methanol moiety: Synthesis and application in the catalytic asymmetric addition of diethylzinc to benzaldehyde

A series of novel N,O-type chiral ligands derived from enantiopure inherently chiral calix[4]arenes containing quinolin-2-yl-methanol moiety in the cone or partial-cone conformation have been synthesized and characterized. Moreover, they have been applied to the catalytic asymmetric addition of diethylzinc to benzaldehyde, which represents the first example that the inherently chiral calixarene can be used as the chiral ligands for the catalytic asymmetric synthesis.     

l‐Lysine‐derived ionic liquids as chiral ligands of Zn(II) complexes used in ligand‐exchange CE

Amino acid ionic liquids (AAILs) with l ‐lysine (l ‐Lys) as anion were synthesized and applied as new chiral ligands in Zn(II) complexes for chiral ligand‐exchange CE. After effective optimization, baseline enantioseparation of seven pairs of dansylated amino acids was achieved with a buffer of 100.0 mM boric acid, 5.0 mM ammonium acetate, 3.0 mM ZnSO₄, and 6.0 mM [C₆mim][l ‐Lys] at pH 8.2. To validate the unique behavior of AAILs, a comparative study between the performance of Zn(II)‐l ‐Lys and Zn(II)‐[C₆mim][l ‐Lys] systems was conducted. In Zn(II)‐[C₆mim][l ‐Lys] system, it has been found that the improved chiral resolution could be obtained and the migration times of the three test samples were markedly prolonged. Then the separation mechanism was further discussed. The role of [C₆mim][l ‐Lys] indicated clearly that the synthesized AAILs could be used as chiral ligands and would have potential utilization in separation science in future.     

C1‐Symmetric Bicyclo[2.2.2]octa‐2,5‐diene (bod*) Ligands in Rhodium‐Catalyzed Asymmetric 1,4‐Addition of Arylboronic Acids to Enones and 1,2‐Addition to N‐[(4‐Nitrophenyl)sulfonyl]imines

A set of ten C₁‐symmetric chiral bicyclo[2.2.2]octa‐2,5‐dienes (bod*) 2 (Fig. 1) were tested as ligands in Rh‐catalyzed arylation reactions. The 1,4‐addition of arylboronic acids to cyclohex‐2‐en‐1‐one, cyclopent‐2‐en‐1‐one, and tert‐butyl cinnamate proceeded smoothly with excellent enantioselectivities (up to 99% ee; Tables 1–3). The challenging 1,2‐addition of triphenylboroxine to N‐[(4‐nitrophenyl)sulfonyl]imines yielded the product in high yield and in good enantioselectivity (up to 92% ee; Table 4). Generally, the use of C₁‐symmetric chiral bod* ligands bearing bulky substituents resulted in lower enantioselectivities, whereas several electron‐poor and electron‐rich bod* ligands gave higher enantioselectivities than the benchmark ligands reported in literature.     

Coordination chemistry of amine bis(phenolate) titanium complexes: tuning complex type and structure by ligand modification

The coordination chemistry of titanium(IV) complexes of amine bis(phenolate) ligands was investigated by synthesizing various types of complexes and analyzing them specroscopically and structurally. Steric effects of tridentate [ONO]- and tetradentate [ONNO]-type ligands were studied by reacting the ligand precursors with titanium tetra(isopropoxide). [ONNO]-type ligands featuring an amine donor located on a pendant arm led to octahedral bis(isopropoxide) complexes, regardless of the steric bulk around the metal. Several such complexes having varying steric crowding were thus synthesized. On the other hand, steric effects were found to play a major role in determining the complex constitution when [ONO]-type ligands, featuring no side donor, were involved. Relatively sterically undemanding ligands led to octahedral bis(homoleptic) complexes, whereas increased steric bulk resulted in the formation of pentacoordinate bis(isopropoxide) complexes. These pentacoordinate complexes readily lead to bis(heteroleptic) complexes by reaction with nonsterically demanding [ONO]- and [ONNO]-type ligand precursors. In the latter case the sidearm nitrogen remains uncoordinated to the metal. The bis(isopropoxide) complexes of the [ONNO]-type ligands may also lead to bis(heteroleptic) complexes, however, these reactions are much slower.     

Enantiopure inherently chiral calix[4]arene derivatives containing quinolin-2-yl-methanol moiety:Synthesis and application in the catalytic asymmetric addition of diethylzinc to benzaldehyde

A series of novel N,O-type chiral ligands derived from enantiopure inherently chiral calix[4]arenes containing quinolin-2-yl-methanol moiety in the cone or partial-cone conformation have been synthesized and characterized. Moreover, they have been applied to the catalytic asymmetric addition of diethylzinc to benzaldehyde, which represents the first example that the inherently chiral calixarene can be used as the chiral ligands for the catalytic asymmetric synthesis. Supported by the National Natural Science Foundation of China (Grant Nos. 20625206 & 20372064), the National Basic Research Project (Grant Nos. 2007CB808000 & 2008CB617501), and the Chinese Academy of Sciences     

Coordination chemistry and biological activity of nickel(II) and copper(II) ion complexes with nitrogen–sulphur donor ligands derived from S-benzyldithiocarbazate (SBDTC)

A bidentate and a quadridentate Schiff base having NS and NNSS donor sequences were prepared by condensing S-benzyldithiocarbazate (NH₂NHCSSCH₂Ph) with 2,3-butanedione (1:1 and 1:2 mole ratio). Ni^II and Cu^II complexes of these ligands were studied and characterised by elemental analyses and various physico-chemical techniques. The nickel complexes, [Ni(NS)₂] and [Ni(SNNS)], were diamagnetic with square-planar and five-coordinate structures, respectively. The copper complex was, however, pentacoordinated. The ligands and the complexes were screened for anticancer activity against T-lymphoblastic leukemic cells (CEM-SS) and colon cancer cells (HT-29). The NS Schiff base was strongly active against leukemic cells with a CD₅₀ value of 2.05 g cm^–3. The nickel and copper complexes were found to be stronger antioxidants than Vitamin E.     

Isoselective Polymerization of rac-Lactide by Highly Active Sequential {ONNN} Magnesium Complexes

The coordination chemistry and the activities in the ring-opening polymerization catalysis of racemic lactide (LA) of magnesium complexes of a series of {ONNN}-type sequential monoanionic ligands are described. All ligands include pyridyl and substituted-phenolate as peripheral groups. The ligands bearing either chiral or meso-bipyrrolidine cores led to single diastereomeric complexes, whereas the ligands bearing a diaminoethane core led to diastereomer mixtures. All {ONNN}Mg-X complexes [X=Cl, HMDS (hexamethyldisilazide)] led to highly active and isoselective catalysts. The complexes bearing the chiral bipyrrolidine core exhibited the highest activities (full consumption of 5000 equiv. of rac-LA at RT within 5 min) and highest isoselectivities (P_m=0.91), as well as a living character. The complexes of the meso-bipyrrolidine based ligands were almost as active and slightly less stereoselective, while those of the diaminoethane based ligands exhibited reduced activities and isoselectivities.     

Synthesis of new planar chiral [2.2]paracyclophane Schiff base ligands and their application in the asymmetric Henry reaction

A series of new planar and central chiral ligands based on [2.2]paracyclophane backbones were designed and prepared from enantiomerically pure 4-amino-13-bromo[2.2]paracyclophane and commercially available chiral amino alcohols. Their application in a copper-catalyzed asymmetric Henry reaction resulted in secondary alcohols with high yield and excellent selectivity for active aldehydes (up to 94% ee). This is a successful example of employing planar chiral [2.2]paracyclophane ligands in copper-catalyzed reaction.     

Nanoscale metal coordination macrocycles fabricated by using "dimeric" dipyrrins

Covalently linked dipyrrin (dipyrromethene) dimers have afforded nanoscale [2+2]-type neutral coordination macrocycles with a diagonal of about 1.6 nm. Two moieties of the achiral dipyrrin-Zn(II) complex yield the chiral coordination macrocycles as minor species, as well as major meso stereoisomers by the covalent linkages. Tetrahedral Zn(II) coordination by using acyclic ligands enables the dipyrrin-metal complex units to readily rotate and pass through the cavity of the nanorings in order to reveal the transitions between the chiral and achiral isomers.     

Synthesis of new binol based [1+1] macrocyclic chiral manganese(III) Schiff bases as catalysts for asymmetric epoxidation

A series of new chiral binol based [1+1] macrocyclic Schiff bases have been synthesized in high yields in short reaction times via cyclo-condensation of dialdehydes with long tethers and chiral diamines. Macrocyclic Mn(salen) complexes containing N₂O₂ salen units incorporated with spacers of increased tether lengths were synthesized and characterized. The newly synthesized catalyst system was successfully employed for the enantioselective epoxidation of unfunctionalized olefins with high yields and good enantioselectivity.     

Chiral Resolution of Spin-Crossover Active Iron(II) [2x2] Grid Complexes

Chiral magnetic materials are proposed for applications in second-order non-linear optics, magneto-chiral dichroism, among others. Recently, we have reported a set of tetra-nuclear Fe(II) grid complex conformers with general formula C/S-[Fe₄L₄]⁸⁺ (L: 2,6-bis(6-(pyrazol-1-yl)pyridin-2-yl)-1,5-dihydrobenzo[1,2-d : 4,5-d′]diimidazole). In the grid complexes, isomerism emerges from tautomerism and conformational isomerism of the ligand L, and the S-type grid complex is chiral, which originates from different non-centrosymmetric spatial organization of the trans type ligand around the Fe(II) center. However, the selective preparation of an enantiomerically pure grid complex in a controlled manner is difficult due to spontaneous self-assembly. To achieve the pre-synthesis programmable resolution of Fe(II) grid complexes, we designed and synthesized two novel intrinsically chiral ligands by appending chiral moieties to the parent ligand. The complexation of these chiral ligands with Fe(II) salt resulted in the formation of enantiomerically pure Fe(II) grid complexes, as unambiguously elucidated by CD and XRD studies. The enantiomeric complexes exhibited similar gradual and half-complete thermal and photo-induced SCO characteristics. The good agreement between the experimentally obtained and calculated CD spectra further supports the enantiomeric purity of the complexes and even the magnetic studies. The chiral resolution of Fe(II)- [2×2] grid complexes reported in this study, for the first time, might enable the fabrication of magneto-chiral molecular devices.     

A novel,C2-symmetric,chiral bis-cyclosulfinamide-olefin tridentate ligand in Rh-catalyzed asymmetric 1,4-additions

A C₂-symmetric, chiral bis-cyclosulfinamide-olefin ligand composed of two 1-oxo-2,3-dihydro-1,2-benzisothiazole moieties with rigid skeletons and a conformationally flexible butenylene chain is disclosed for the first time. HRMS and ¹H NMR analyses verify that the in situ-generated complex of the ligand and [Rh(C₂H₄)₂Cl]₂ possesses a rhodium (I) center coordinated to the tridentate ligand via two sulfinyl moieties and a CdbndC bond. The chiral ligand provided extremely high enantioselectivity (up to >99%ee) in the Rh-catalyzed asymmetric 1,4-additions of arylboronic acids to cyclohexenone and cyclopentenone. The tridentate ligand gave much higher enantioselectivity than the analogous chiral bidentate ligands.     

Phosphine-catalyzed [4+2] cycloaddition of sulfamate-derived cyclic imines with allenoates: synthesis of sulfamate-fused tetrahydropyridines

Using n-PrPPh₂ as the nucleophilic catalyst, the [4+2] cycloaddition reaction of the sulfamate-derived cyclic imines with allenoates works efficiently to yield various sulfamate-fused tetrahydropyridines in high yields with excellent diastereoselectivities. Using amino acid-based bifunctional phosphine as chiral catalyst, an asymmetric [4+2] cycloaddition reaction was achieved, giving chiral sulfamate-fused tetrahydropyridines in high yields with good enantiomeric excesses.     

Utility of the iridium complex of the pybox ligand in regio- and enantioselective allylic substitution

The viability of the iridium complex of pybox as chiral catalyst in allylic substitutions and the enantioselective synthesis of branched products was studied. Among several chiral ligands evaluated, the iridium complex of pybox having a phenyl group catalyzed the reaction with high activity to form the branched amines with good enantioselectivities when hydroxylamine, amine, and aniline were employed as a nucleophile. The allylic substitution with oximes proceeded smoothly to give the branched oxime ethers with good enantioselectivities. [reaction: see text]     

Darstellung und NMR-spektroskopische Charakterisierung von konfigurationsstabilen Diorganozinn(IV)-Komplexen RPhSnL mit Zinn als chiralem Zentrum

Synthesis and Characterization of Configurationally Stable Diorganotin(IV) Complexes with Tin as a Chiral Centre Contrary to the high optical stability of tetraorganotin compounds most heteroleptic organic tin compounds are configurationally instable. We report the synthesis and the characterization of some new enantiomeric and diastereomeric diorganotin(IV) complexes of stable configuration with tin as a chiral centre. The stabilization of the chiral tin atom was realized by complexation with tridentate diacidic esterhydrazone ligands H₂L, which prevent an interconversion at the stereogenic centre. Multinuclear NMR-studies in solution demonstrate, that the configuration of the chiral tin center is configurationally stable up to 160°C. The molecular structure of the complexes Neophyl-phenyl-tin-2[(2-methyl-mercaptothiocarbonyl)-hydrazono]propionate II b and (2-Methyl-butyl-1-yl)-phenyl-tin-[S-methyl-β-N-(2-salicylmethylidene)thiocarbazat] III g have been determined by single crystal X-ray diffraction analysis.     

Rhodium-Catalyzed Enantioselective Synthesis of Highly Fluorescent and CPL-Active Dispiroindeno[2,1-c]fluorenes

The enantioselective synthesis of chiral [7]-helical dispirodihydro[2,1-c]indenofluorenes (DSF-IFs) was achieved for the first time in good yields with high er values (er up to 99 : 1). The crucial step of the whole reaction sequence was the enantioselective intramolecular [2+2+2] cycloaddition of tethered triynediols to indenofluorenediols, which was catalyzed by a Rh/SEGPHOS® complex. Further transformations led to the corresponding DSF-IFs. The prepared helically chiral DSF-IFs combine circularly polarized luminescence (CPL) activity (g_lum=∼10⁻³) with exceptionally high fluorescence quantum yields (up to Φ_lum=0.97).     

New Types of Planar Chiral [2.2]Paracyclophanes and Construction of One‐Handed Double Helices

New types of planar chiral (R_p)‐ and (S_p)‐4,7,12,15‐tetrasubstituted [2.2]paracyclophanes were synthesized from racemic 4,12‐dihydroxy[2.2]paracyclophane as the starting compound. Regioselective dibromination and transformation afforded a series of planar chiral (R_p)‐ and (S_p)‐4,7,12,15‐tetrasubstituted [2.2]paracyclophanes, which can be used as chiral building blocks. In this study, left‐ and right‐handed double helical structures were constructed via chemoselective Sonogashira–Hagihara coupling. The double helical compounds were excellent circularly polarized luminescence (CPL) emitters with large molar extinction coefficients, good photoluminescence quantum efficiencies, and large CPL dissymmetry factors.