An efficient route to pyridine and 2,2′-bipyridine macrocycles incorporating a triethylenetetraminetetraacetic acid core as ligand for lanthanide ions

Two novel macrocyclic chelators L₁ and L₂ incorporating an intracyclic pyridine or 2,2′-bipyridine unit and a triethylenetetraminetetraacetic acid core (TTTA) were synthesized with the aim of forming lanthanide complexes suitable as efficient long-lived luminophores. For this goal, an efficient methodology for the preparation of TTTA derivatives using prealkylated precursors is described. Starting from commercially available compounds, the target ligands were obtained in seven (L₁) and nine (L₂) steps in 40% and 20% overall yields, respectively. Stable Tb(III) complexes were prepared and displayed interesting luminescence properties.     

Luminescent heptadentate Tb complex with pendant aza-15-crown-5 showing recognition of lactate and salicylate in aqueous solution

The coordinatedly unsaturated neutral complex TbL1 that possesses two labile metal-bound water molecules provides linear response to lactate in the range of 0-3.0 mM at the simulated extracellular background with the variations of Tb luminescence lifetime as output; the maximal amplification of the luminescence intensity of TbL1 reaches a factor of 135 upon titration with aromatic antenna salicylate in the physiological pH window.     

Synthesis and structural characterization of novel zinc(II) and cadmium(II) complexes with pyridine-phosphine chalcogenide ligands

New pyridine-phosphine chalcogenide ligands, tris[2-(2-pyridyl)ethyl]phosphine sulfide 1a and tris[2-(2-pyridyl)ethyl]phosphine selenide 1b, react with zinc(II) and cadmium(II) chlorides in EtOH at room temperature to afford complexes of compositions 2ZnCl₂·2L (2, L = 1a) and 3CdCl₂·2L (3a,b, L = 1a,b) in high yields. The solid-state structure of complexes 2, 3 has been proved by X-ray analysis data. Complex 2 is a centrosymmetric dimer, where two atoms of zinc are bonded by two bridging pyridine-phosphine sulfide ligands through N atoms. Complexes 3a,b exist as polymeric chains with each bridging ligand acting as a chelate N,S- or N,Se-donor to one cadmium(II) center and as a pyridine N-donor to the next cadmium(II) center.     

Molecular assemblies of trichloride neodymium and europium complexes chelated by 1,10-phenanthroline

Four trichloride lanthanide (neodymium or europium) complexes (1-4) have been solvothermally synthesized with the 1,10-phenanthroline (phen) chelate in ethanol solvent and their structures have been characterized by single-crystal X-ray diffraction analysis. Depending on the Ln/phen ratio, different motif nuclearities have been observed. With Ln/phen = 1/2, a dinuclear species with μ₂-Cl₂ edge-sharing bridge is formed with neodymium, NdCl₃(phen)₂ (1), whereas a mononuclear complex appears with europium, EuCl₃(phen)₂ (4) with an unusual pentagonal bipyramid for the lanthanide center (coordination 7). When Ln/phen ratio increases (1/1), an identical complex is obtained with Nd (2) or Eu (3). It is a monohydrated complex LnCl₃(H₂O)(phen)₂ with one water molecule completing the coordination sphere of the lanthanide. For all compounds, each rare-earth cation is chelated by two distinct phen ligands. Thermal behavior of complexes 1 and 2 are discussed (by means of thermogravimetric analysis and X-ray thermodiffraction) as well as the luminescence spectra of europium-based complexes 3 and 4 (Supplementary Material).     

Osmium assisted C-H activation and CN cleavage of N-(2′-hydroxyphenyl) benzaldimines. Synthesis, structure and electrochemical properties of some organoosmium complexes

Reaction of N-(2′-hydroxyphenyl)-4-R-benzaldimines (L-R, R = OCH₃, CH₃, H, Cl and NO₂) with [Os(PPh₃)₃Br₂] in refluxing 2-methoxyethanol in the presence of triethylamine affords two families of organoosmium complexes (1-R and 2-R). In both 1-R and 2-R complexes a benzaldimine ligand is coordinated to the metal center as tridentate C,N,O-donor. In the 1-R complexes, a bidentate N,O-donor imionsemiquinonate ligand, derived from the hydrolysis of another benzaldimine, and a PPh₃ ligand are also coordinated to osmium. In the 2-R complexes, a carbonyl, derived from decarbonylation of 4-R-benzaldehyde (derived from the same hydrolysis stated above), and two PPh₃ ligands take up the remaining coordination sites on osmium. Structures of the 1-Cl and 2-OCH₃ complexes have been determined by X-ray crystallography. All the 1-R and 2-R complexes are diamagnetic, and show characteristic ¹H NMR signals and intense MLCT transitions in the visible region. Cyclic voltammetry on the 1-R complexes shows a reversible Os(III)-Os(IV) oxidation within 0.47-0.67 V (vs SCE), followed by an irreversible oxidation of the imionsemiquinonate ligand within 1.10-1.36 V. An irreversible Os(III)-Os(II) reduction is also displayed by the 1-R complexes within −1.02 to −1.14 V. Cyclic voltammetry on the 2-R complexes shows a reversible Os(II)-Os(III) oxidation within 0.29-0.51 V, followed by a quasi-reversible oxidation within 1.04-1.29 V, and an irreversible reduction of the coordinated benzaldimine ligand within −1.16 to −1.31 V.     

Synthesis,characterization and photophysical properties of the pincer platinum(II) complexes with m-bis(benzimidazol-2′-yl)benzene ligand

The reaction of 2,2′-(1,5-dibutoxy-2,4-phenylene)bis(1-phenyl-1H-benzo[d]imidazole) (1) with K₂PtCl₄ in refluxing HOAc afforded the pincer Pt(II) chloride complex 2. Treatment of 2 with KI gave the corresponding Pt(II) iodide complex 3. While reaction of 2 with 4-(methoxy)phenylacetylene in the presence of NaOH easily produced the Pt(II) acetylide complex 4. All of the new compounds have been well characterized by elemental analysis (HRMS for 1), NMR, and IR spectra. Additionally, the molecular structures of Pt(II) complexes 2–4 have been determined by X-ray single-crystal diffraction. The electronic absorption and photoluminescent properties of Pt(II) complexes 2–4 have been investigated. The same level time-dependent density functional theory (TD-DFT) calculations were carried out by using the Gaussian 09 program package. All of the platinum complexes investigated in this study have exhibited luminescence in CH₂Cl₂ solution, in the solid state and in glass 2-MeTHF solution at 77 K, displaying vibronically structured emission profiles. The luminescence quantum yields in CH₂Cl₂ solution are 0.05–0.06 and the emission lifetimes are in microsecond range.     

Self-assembly of a tridentate Schiff-base ligand with Zn(II) in the presence of lanthanides: Novel crystal structures and spectroscopic properties

Condensation of picolinaldehyde with methyl 4-amino-3-hydroxy-benzoate resulted in the acquisition of a tridentate Schiff-base ligand (HL) which contains a structural moiety typical of octahedrally cored grid-type analogs. Reactions of HL with Zn(NO₃)₂ in the presence of Ln(NO₃)₃ [Ln = Sm(III), Tb(III) and Yb(III)] result in two types of complexes, viz. [Zn(HL)(L)]₂[Ln(NO₃)₅] [Sm(III), 1a and Tb(III), 1b] and [Zn(HL)L]₂[Yb(NO₃)₅]·C₃H₆O (1c). Despite applying two different synthetic protocols, the transition metal ion displayed a greater propensity towards the meridional tridentate pocket, which is reflected by XRD analysis, the ESI-MS technique and further supported by elemental analysis and IR characterization of each compound. In addition, we have compared the luminescence properties of 1a, 1b and 1c with the previously synthesized [Zn(HL)(L)]₂[Zn(NO₃)₄] (1d) to investigate whether a different metal in the outer coordination sphere could somehow tune the compounds’ spectral behavior.     

Preparation of three terbium complexes with p-aminobenzoic acid and investigation of crystal structure influence on luminescence property

Three new rare earth p-aminobenzoic acid complexes, [Tb₂L₆(H₂O)₂]_n (1), [Tb₂L₆(H₂O)₄]·2H₂O (2) and [Tb(phen)₂L₂(H₂O)₂](phen)L·4H₂O (3) (HL: p-aminobenzoic acid; phen: 1, 10-phenanthroline), with different structural forms are reported in this paper. Complex 1 is a polymolecule with a two-dimensional plane structure. Compound 2 is a binuclear molecule, and 3 appears to be a mononuclear complex. The fluorescence intensity, the fluorescence life-time and emission quantum yield of 2, which has two coordination water molecules, is better than those of 1, which has only one coordination water molecule. This is an unusual phenomenon for general fluorescent rare earth complexes. The fluorescence performance of 3 is the most unsatisfactory among the three complexes. Their crystal structures show that the coordination mode of the ligand is an important factor influencing the luminescence properties of a fluorescent rare earth complex.     

Nickel and cationic palladium complexes bearing (imino)pyridyl alcohol ligands: Synthesis, characterization and vinyl polymerization of norbornene

A series of nickel and palladium complexes bearing (imino)pyridyl alcohol tridentate [N,N,O] ligands, 2-(ArNCMe)-6-{(HO)CR₂}C₅H₃N (L1-L4), were synthesized and sufficiently characterized by elemental and spectroscopic analysis along with X-ray diffraction analysis. The X-ray diffraction demonstrated that five-coordinated nickel halide complexes (1a-4a and 1b) and six-coordinated nickel acetate complex (1c) were prepared, and cationic palladium complexes (1d and 2d) formed with the [PdCl₄]²⁻ counterion. All these complexes displayed high catalytic activities up to 1.883 × 10⁷ g(PNB) mol⁻¹(cat) h⁻¹ (2d) for the vinyl polymerization of norbornene on treatment with excess methylaluminoxane (MAO), affording the vinyl-type PNBs with high molecular weights and relatively narrow molecular weight distributions. The parameters of reaction conditions, the type of metals and steric effects of coordinative ligands had influences on the catalytic properties.     

Chiral organotin (IV) carboxylates complexes: Syntheses, characterization, and crystal structures with chiral (S)-(+)-6-methoxy-α-methyl-2-naphthaleneaceto acid ligand

Eight new organotin (IV) carboxylates, (R₃Sn)₄(nap)₄ (R = Me 1, n-Bu 2), [(R₃Sn) (nap)]_n (R = Ph 3, PhCH₂4), (R₂Sn) (nap)₂ (R = n-Bu 5, Ph 6, PhCH₂7) and {[R₂Sn(nap)]₂O}₂ (R = Me 8) (nap = (S)-(+)-6-methoxy-α-methyl-2-naphthaleneaceto anion) have been synthesized. All of the complexes have been characterized by elemental analysis, FT-IR, NMR (¹H, ¹³C and ¹¹⁹Sn) spectra. Among these complexes, complexes 1, 3, 5 and 8 were also characterized by X-ray crystallography diffraction analysis, and the data of X-ray crystallography diffraction indicated that complexes 1, 3 and 5 are new chiral organotin (IV) carboxylates complexes. The structural analyses show that complex 1 has a tetranuclear Sn₄O₈ macrocycle structure, complex 3 has a 1D spring-like chiral helical chain with a columnar channel, complex 5 possesses a dimer structure, and complex 8 has a supramolecular chainlike ladder structure through weak intermolecular non-covalent O^…O interactions.     

The reactivity of TMSN3 with ruthenium cyclopropenyl complexes containing different ligands and different substituent at Cγ

Ruthenium vinylidene complexes 2a-2c containing indenyl and bidentate dppe ligands can be obtained in efficient yields. Treatment of the cationic ruthenium vinylidene complexes with n-Bu₄NOH in acetone yields the neutral cyclopropenyl products (η⁵-C₉H₇)(dppe)Ru-CC(Ph)CHR (3) (3a, R = Ph; 3b, R = CN; 3c, R = p-C₆H₄-CN) via the deprotonation reaction. Reaction of complexes 3a and 3c with Me₃SiN₃ (TMSN₃) the N-coordinated complexes 4a and 4c can be obtained as stable products. Complex 3b containing CN group at Cγ in the cyclopropenyl ring reacts with TMSN₃ yielded the tetrazolate complex 5b. Similar cyclopropenyl products containing indenyl and two triphenylphosphine ligands 3′ can also be synthesized. Reaction of complex 3b′ with TMSN₃ also yielded the tetrazolate complex as the major product. And the minor products are [Ru]-N₃ and organic compound 6b. Reaction of 3a′ and 3c′ with TMSN₃ yielded [Ru]-N₃. The corresponding organic products can also be obtained via the N₃⁻ attacking the metal center in the N-coordinated complexes 4a′ and 4c′.     

Trinuclear copper(I) acetylide complexes bearing carbonyl moiety: Synthesis, characterization, and photophysical properties

A series of trinuclear copper(I) acetylide complexes with carbonyl moiety, [Cu₃(μ-dppm)₃(μ₃-η¹-CCC(O)R)₂](ClO₄) (R = H (1), CH₃ (2), OCH₃ (3), NH₂ (4), NEt₂ (5)) (dppm = bis(diphenylphosphino)methane), have been synthesized and characterized. The crystal structures of [Cu₃(μ-dppm)₃(μ₃-η¹-CCC(O)CH₃)₂](ClO₄) (2) and [Cu₃(μ-dppm)₃(μ₃-η¹-CCC(O)NH₂)₂](ClO₄) (4) were determined by X-ray diffraction. The photophysical properties of complexes 1−5 have been studied. Complexes 1−5 show luminescence both in the solid state and in acetonitrile solution at 298 K, and their emission energies are in the order: 5 > 4 > 3 > 2 > 1. Density function theory (DFT) calculations at the hybrid Perdew, Burke, and Ernzerhof functional (PBE1PBE) level were performed on model complex 1 to elucidate the emission origin of complexes 1−5.     

Synthesis and structural chemistry of bis(pyridylimino)isoindolato-ruthenium complexes and their activity as mediators in the atom transfer radical polymerization (ATRP) of styrene

The reaction of the Bispyridyl Isoindole (BPI) type ligands L1 and L2 (L1 = 1,3-Bis(2-(4-tert-butylpyridyl)imino) isoindole, L2 = 1,3-Bis(2-(5-bromo)imino)-5,6-dimethylisoindole) with [Ru(μ-Cl)₂(cod)]_x in presence of triethylamine using coordinating solvents like acetonitrile, dimethyl sulfoxide or pyridine cleanly gave the complexes [{BPI(L1,L2)}Ru^II(Cl)(S)₂] (L1: S = acetonitrile (1), dimethyl sulfoxide (2), pyridine (3); L2: S = acetonitrile (4), dimethyl sulfoxide (5), pyridine (6)). In these complexes the BPI ligands meridionally coordinated to the ruthenium center as established by X-ray diffraction for complexes 3 and 6. The catalytic activity in the direct ATRP (Atom Transfer Radical Polymerization) of styrene was tested for complexes 1-6.     

Cellular uptake, cytotoxicity, apoptosis, antioxidant activity and DNA binding of polypyridyl ruthenium(II) complexes

Ruthenium(II) polypyridyl complexes [Ru(phen)₂(APIP)](ClO₄)₂1 and [Ru(phen)₂(HAPIP)](ClO₄)₂2 have been synthesized and characterized. The DNA-binding behaviors were investigated by electronic absorption titration, luminescence spectra, viscosity measurements, thermal denaturation and photoactivated cleavage. The DNA-binding constants K_b for complexes 1 and 2 were determined to be 3.38 (±0.42) × 10⁵ M⁻¹ (s = 1.48) and 3.93 (±0.60) × 10⁵ M⁻¹ (s = 3.14), respectively. The studies on the photocleavage demonstrated that the effects of cleavage are concentration-dependent. The results showed that complexes 1 and 2 interact with CT-DNA by intercalative mode. The cytotoxicity of complexes 1 and 2 has been evaluated by MTT method. The apoptosis assay was carried out with acridine orange/ethidium bromide (AO/EB) staining methods. The cellular uptake showed that complexes can enter into the cytoplasm and accumulate in the nuclei. The antioxidant activity studies suggested that the ligands and complexes may be potential drugs to eliminate the radical.     

Functional luminescent lanthanide complexes: Modulation of visible luminescence from europium complexes

The syntheses of three new ligands (L^1-3), which are based upon a DO3A core and appended with additional receptor sites for metal cations, are described, together with their corresponding Eu(III) complexes (Eu-L^1-3). The complexes are visibly luminescent in aqueous solution, following sensitization via the pyridine chromophore, showing characteristic narrow line-like emission from Eu(III). The luminescence properties show that water is effectively excluded from the inner coordination sphere of europium (q = 0). Each of the complexes showed perturbed luminescence properties upon addition of a variety of d-block metal ions. For example, emission quenching was observed for each complex following addition of Cr(III) and Cu(II). Selectivity towards Hg(II) (over Cd(II), Cu(II) and Zn(II)) was demonstrated with Eu-L³, which possesses a receptor site incorporating a softer thiophene moiety. More specifically, Hg(II) binding resulted in changes in the form of the steady state emission spectrum, together with a corresponding reduction of the luminescence lifetime in water, which can be attributed to an increase in inner sphere hydration (q = 2) and thus enhanced non-radiative deactivation of the ⁵D₀ state by proximate O-H oscillators.     

Syntheses, structural characterizations and properties of 12-MC-4 organotin(IV) metallacrowns: [12-MCRSn(IV)N(shi)-4] and [12-MCRSn(IV)N(Clshi)-4] (R = Et, Bu, Ph; H3shi = salicylhydroxamic acid; H3Clshi = 5-chlorosalicylhydroxamic acid)

Five 12-MC-4 organotin(IV) metallacrowns(MCs) with the types of [12-MC_{RSn(IV)N(shi)}-4] (R = Et (1), Bu (2), Ph (3); H₃Shi = salicylhydroxamic acid) and [12-MC_{RSn(IV)N(Clshi)}-4] (R = Et (4), Bu (5), H₃Clshi = 5-chlorosalicylhydroxamic acid) have been synthesized and characterized by elemental analyses, IR and TGA. X-ray single-crystal diffraction analyses were also carried out and showed that all complexes 1-5 contain a neutral 12-membered metallacrown ring which is formed by the succession of four repeating units of -[Sn-N-O]-, indicating the substituents on the tin(IV) atom are uninfluential in coordination of organotin(IV) centers with hydroxamic acid. Fluorescence properties of complexes 1-5 have been investigated, where complex 3 displays strong fluorescence emissions in the blue region. In addition, antitumor activities of complexes 4 and 5 have also been tested, and both the complexes exhibit weak activity towards human hepatocellular carcinoma cell line (Bel-7402) and Hela cell line.     

Synthesis and characterization of half-sandwich Rh, Ir complexes containing mono-thiolate-ortho-carborane ligand

Two binuclear complexes [Cp^∗M(Cl)Carb^S]₂ (Cp^∗ = η⁵-C₅Me₅, M = Rh (1a), Carb^S = SC₂(H)B₁₀H₁₀, Ir (1b)) were synthesized by the reaction of LiCarb^S with the dimeric metal complexes [Cp^∗MCl(μ-Cl)]₂ (M = Rh, Ir). Four mononuclear complexes Cp^∗M(Cl)(L)Carb^S (L = BuⁿPPh₂, M = Rh (2a), Ir (2b); L = PPh₃, M = Rh (4a), Ir (4b)) were synthesized by reactions of 1a or 1b with L (L = BuⁿPPh₂ (2); PPh₃ (4)) in moderate yields, respectively. Complexes 3a, 3b, 5a, 5b were obtained by treatment of 2a, 2b, 4a, 4b with AgPF₆ in high yields, respectively. All of these compounds were fully characterized by IR, NMR, and elemental analysis, and the crystal structures of 1a, 1b, 2a, 2b, 4a, 4b were also confirmed by X-ray crystallography. Their structures showed 3a, 3b and 5a, 5b could be expected as good candidates for heterolytic dihydrogen activation. Preliminary experiments on the dihydrogen activation driven by these half-sandwich Rh, Ir complexes were done under mild conditions.     

Synthesis, structure, and catalytic activity of rhodium complexes with new chiral binaphthyl-based NHC-ligands

Three new chiral NHC-rhodium complexes have been prepared from the reactions between [Rh(COD)Cl]₂, NaOAc, KI, and dibenzimidazolium salts 3, 4 or 5, which are derived from (S)-2,2′-diamino-1,1′-binaphthyl. The steric and electronic effects of the ligand play an important role in the complex formation. For example, treatment of pyridine substituted dibenzimidazolium salts 3 or 4 with 0.5 equiv of [Rh(COD)Cl]₂ in the presence of NaOAc and KI in CH₃CN at 85 °C gives the chiral Rh(III) complexes 6 and 7, respectively. However, under similar reaction conditions, pyridine-N-oxide substituted dibenzimidazolium salt 5 affords a binuclear Rh(I) complex 8. All compounds have been characterized by various spectroscopic techniques, and elemental analyses. The solid-state structures of compounds 4-8 have been further confirmed by X-ray diffraction analyses. Rhodium complexes 6-8 show good catalytic activity for the asymmetric hydrosilylation of acetophenone with moderate ee values.     

Targeting nitric oxide synthase with Tc/Re-tricarbonyl complexes containing pendant guanidino or isothiourea moieties

The visualization of inducible nitric oxide synthase (iNOS) in vivo with specific radioactive probes could provide a valuable insight into the diseases associated with upregulation of this enzyme. Aiming at that goal, we have synthesized a novel family of conjugates bearing a pyrazolyl-diamine chelating unit for stabilization of the fac-[M(CO)₃]⁺ core (M = ^99mTc, Re) and pendant guanidino (L¹ = guanidine, L² = N-hydroxyguanidine, L³ = N-methylguanidine, L⁴ = N-nitroguanidine) or S-methylisothiourea (L⁵) moieties for iNOS recognition. L¹-L⁵ reacted with fac-[M(CO)₃(H₂O)]⁺, yielding complexes of the type fac-[M(CO)₃(k³-L)]⁺ (M = Re/^99mTc; 1/1a, L = L¹; 2/2a, L = L²; 3/3a, L = L³; 4/4a, L = L⁴; 5/5a, L = L⁵), which were fully characterized by the usual analytical methods in chemistry and radiochemistry, including X-ray diffraction analysis in the case of 1. The rhenium complexes 1-5 were prepared as “cold” surrogates of the ^99mTc(I) complexes. Enzymatic assays with murine purified iNOS demonstrated that L¹, L², 1 and 2 are poor NO-producing substrates. These assays have also shown that metallation of L⁴ and L⁵ (K_i > 1000 μM) gave complexes with increased inhibitory potency (4, K_i = 257 μM; 5, K_i = 183 μM). The organometallic rhenium complexes permeate through LPS-treated RAW 264.7 macrophage cell membranes, interacting specifically with the target enzyme, as confirmed by the partial suppression of NO biosynthesis (ca. 20% in the case of 4 and 5) in this cell model. The analog ^99mTc(I)-complexes 1a-5a are stable in vitro, being also able to cross cell membranes, as demonstrated by internalization studies in the same cell model with compound 4a (4h, 37 °C; 33.8% internalization). Despite not being as effective as the α-amino-acid-containing metal-complexes previously described by our group, the results reported herein have shown that similar ^99mTc(I)/Re(I) organometallic complexes with pendant amidinic moieties may hold potential for targeting iNOS expression in vivo.     

Synthesis and structure of {{amino(triorganosilyl)carbene}pentacarbonyltungsten(0)} complexes and attempted synthesis of {[2-bis(trimethylsilyl)methyl-3-triorganosilyl-2H-azaphosphirene-κP]pentacarbonyltungsten(0)}

First examples of tungsten aminocarbene complexes [(OC₅)W{C(SiR¹_nR²_3-n)NH₂}] 2a-d (R¹ = Ph, R² = Me) were synthesized via ammonolysis of the corresponding methoxycarbene complexes 1a-d. They were characterized by NMR spectroscopy, MS, IR, UV/Vis and elemental analysis, and in the case of the C-triphenylsilyl derivative 2a by single-crystal X-ray structure analysis. The reaction of P-chloro alkylidenephosphane 3 with complexes 2a-d, meant to give 2H-azaphosphirene complexes, was monitored by ³¹P NMR spectroscopy to reveal the formation of the products 4-7, which were presumably formed via decomposition of the transient complexes 10a-d.