Amido Nitrogen Research Articles

Homoleptic chromium(II) aminopyridinates: Transoid vs cisoid coordination

Rare homoleptic divalent chromium complexes have been isolated by reacting two equivalents of sterically bulky deprotonated 2–aminopyridine ligands, N–(2,4,6–trimethylphenyl)–[6–(2,4,6–trimethylphenyl)–pyridine–2–yl]–amine (1), N–(2,6–diisopropylphenyl)–[6–(2,6–dimethylphenyl)–pyridine–2–yl]–amine (2) and N–(2,6–diisopropylphenyl)–[6–(2,4,6–trimethylphenyl)–pyridine–2–yl]–amine (3) with CrCl2 in tetrahydrofuran (THF). Reaction of deprotonated 1 proceeds smoothly at room temperature while that of sterically more bulky 2 and 3 at reflux temperature. The respective bis(aminopyridinate) Cr complexes (4–6) are monomeric and show different orientations of the coordinated ligands. For compound 5, two isomers were identified. For 4 and 5a the two ligands show head to tail arrangement while in 5b and 6 the two ligands adopt the unknown head to head arrangement of aminopyridinato ligands. All the complexes show distorted square planar geometries around the chromium center. For 4 and 5a in which the ligands are coordinated in transoid manner the pyridine rings and amido nitrogen atom lie in the coordination plane of chromium. Hirshfeld analyses showed that H∙∙∙H and H∙∙∙C/C∙∙∙H π–interactions were the main and at times the strongest contributions for the intermolecular interactions.

Spectroscopic Characterization, Thermogravimetry and Biological Studies of Ru(III), Pt(IV), Au(III) Complexes with Sulfamethoxazole Drug Ligand

Complexes of Ru(III), Pt(IV), and Au(III) with sulfamethoxazole (SMX) were experimentally produced. The resulted formations of novel metal complexes were discussed using several techniques, such as effective magnetic moment molar conductivity, IR, UV, and 1H NMR spectra, elemental analyses, thermal analysis, microscopic and XRD analyses. The X-ray diffraction patterns of the solid powders of the synthesized sulfamethoxazole complexes indicated their identical formulation. The surface uniformity of the complexes’ samples was confirmed by SEM images. These complexes appear as spots, dark in appearance, with particle sizes of 100–200 nanometers in transmission electron microscopy (TEM) pictures. The sulfamethoxazole ligand was shown to be bidentate coordinated to the metallic ions with sulfonyle oxygen and amido nitrogen groups, according to IR spectral data. Both Ru(III) and Au(III) complexes have an electrolytic nature, but the Pt(IV) complex has non-electrolytic properties. TG and DTG experiments proved the assigned composition and provided information regarding the thermal stability of complexes in a dynamic air atmosphere, according to the thermal analysis. The effect of the novel prepared complexes was examined for antibacterial and antifungal activity in vitro against a variety of pathogens, and they exceeded the sulfamethoxazole ligand in antibacterial activity. It was observed that the Pt(IV) complex has the ultimate activity versus all the assessed organisms relative to all compounds.

Low-Coordinate Dinuclear Dysprosium(III) Single Molecule Magnets Utilizing LiCl as Bridging Moieties and Tris(amido)amine as Blocking Ligands

A low-coordinate dinuclear dysprosium complex {[Dy(N3N)(THF)][LiCl(THF)]}2 (Dy2) with a double bridging ‘LiCl’ moiety and tris(amido)amine (N3N)3− anions as a blocking ligand is synthesized and characterized structurally and magnetically. Thanks to the use of the chelating blocking ligand (N3N)3− equipped with large steric –SiMe3 groups, the coordination sphere of both DyIII ions is restricted to only six donor atoms. The three amido nitrogen atoms determine the orientation of the easy magnetization axes of both DyIII centers. Consequently, Dy2 shows slow magnetic relaxation typical for single molecule magnets (SMMs). However, the effective energy barrier for magnetization reversal determined from the AC magnetic susceptibility measurements is much lower than the separation between the ground and the first excited Kramers doublet based on the CASSCF ab initio calculations. In order to better understand the possible influence of the anticipated intramolecular magnetic interactions in this dinuclear molecule, its GdIII-analog {[Gd(N3N)(THF)][LiCl(THF)]}2 (Gd2) is also synthesized and studied magnetically. Detailed magnetic measurements reveal very weak antiferromagnetic interactions in Gd2. This in turn suggests similar antiferromagnetic interactions in Dy2, which might be responsible for its peculiar SMM behavior and the absence of the magnetic hysteresis loop.

Spectroscopic characterization, structural investigation, DFT study, and Hirshfeld surface analysis of rhodium and ruthenium amido azo complexes

The reaction of 2,2′-diaminoazobenzene, (H2L) [where H represents the dissociable amino protons], with RhCl3 and Ru(dmso)4Cl2 separately afforded the new homoleptic mononuclear amido azo complexes [Rh(HL)2]Cl (1) and [Ru(HL)2](ClO4)2 (2), respectively. Complex 1 & 2 were characterised by spectroscopic technique and confirmed by x-ray structure determination. Both the complexes, the ligand coordinates meridionally to the metal centre (Rh & Ru) through amido-N, azo-N, and amine-N via single NH deprotonation to form five- and six-membered chelate rings. Solid-state x-ray structure of compounds 1 and 2 revealed an approximately octahedral environment about metals. Both the complexes are twofold crystallographically imposed symmetry with the metals (Rh & Ru) atom in a distorted octahedral environment consisting of six nitrogen atoms from two ligand molecules. In the crystals of [Rh(HL)2]Cl, characteristic networks are built up by πCH—Cl stacking and/or hydrogen bonding interactions between amino nitrogen of complex cations with counter chloride anions. The chain like crystal structures of [Ru(HL)2](ClO4)2 are stabilized by the direct hydrogen-bonding networks between amino (NH2) and amido (NH) nitrogen atoms complex cations with perchlorate anions. Redox properties of the new complexes are examined. DFT calculation were performed to calculate the energy gaps between different orbitals and to correlate the bond lengths and bond angles of complex 1 and 2 with experimental data. Hirshfeld surface analysis and two dimensional finger print plots were performed to describe the intermolecular interactions along contact contribution in the crystalline molecules.

Synthesis, structural and physicochemical properties of a series of manganese(II) complexes with a novel N5 tripodal-amidate ligand and their potential use as water oxidation catalysts

Water oxidation plays a crucial role in both natural and artificial photosynthesis, which is an attractive solution to the depletion of fossil fuels as energy sources due to the increasing consumption. Thus, the search for oxygen evolution reaction catalysts is a hot topic of research. Reaction of the N5-tripodal amidate ligand, N-{2-[(bis(pyridine-2-ylmethyl)amino)methyl]phenyl}picolinamide (Htrip) with MIIX2 (X = Cl-, Br-, I-), in anhydrous ethyl alcohol, and C2H5ONa yields the complexes [MnII(trip)Cl] (1), [MnII(trip)Br] (2), and [MnII(trip)I] (3). Single crystal X-ray structure analysis of 1–3 revealed that the manganese(II) atom in the three manganese compounds occupies the center of a distorted octahedral coordination sphere consisting of two pyridine, one picoline and one amino nitrogen atoms on the equatorial plane, while the axial positions are occupied by one amido nitrogen atom and the halogen anion. The three manganese(II) complexes 1–3 constitute the first examples of mononuclear {MnII(N5trip)X} species to be reported. Magnetic susceptibility measurements showed that these complexes are high-spin d5 systems. Cyclic voltametric study of 1–3 revealed an unexpected two electron, electrochemically reversible redox process, assigned to the oxidation of MnII to MnIV. The electrochemical properties for oxygen evolution reaction of complexes 1–3 showed that the oxidized trip- ligand is responsible for the electrocatalytic oxidation of water to dioxygen.

Synthesis, Structural and Physicochemical Properties of a Series of Manganese(II) Complexes with a Novel N5 Tripodal-Amidate Ligand and Their Potential Use as Water Oxidation Catalysts

Water oxidation plays a crucial role in both natural and artificial photosynthesis, which is an attractive solution to the depletion of fossil fuels as energy sources due to the increasing consumption. Thus, the search for oxygen evolution reaction catalysts is a hot topic of research. Reaction of the N5-tripodal amidate ligand, N-{2-[(bis(pyridine-2-ylmethyl)amino)methyl]phenyl}picolinamide (Htrip) with MIIX2(X=Cl-, Br-, I-), in anhydrous ethyl alcohol, and C2H5ONa yields the complexes [MnII(trip)Cl] (1), [MnII(trip)Br] (2), and [MnII(trip)I] (3). Single crystal X-ray structure analysis of 1-3 revealed that the manganese(II) atom in the three manganese compounds occupies the center of a distorted octahedral coordination sphere consisting of two pyridine, one picoline and one amino nitrogen atoms on the equatorial plane, while the axial positions are occupied by one amido nitrogen atom and the halogen anion. The three manganese(II) complexes 1-3 constitute the first examples of mononuclear {MnII(N5trip)X} species to be reported. Magnetic susceptibility measurements showed that these complexes are high-spin d5 systems. Cyclic voltametric study of 1-3 revealed an unexpected two electron, electrochemically reversible redox process, assigned to the oxidation of MnII to MnIV. The electrochemical properties for oxygen evolution reaction of complexes 1-3 showed that the oxidized trip- ligand is responsible for the electrocatalytic oxidation of water to dioxygen.

Platinum(II) Complexes of Tridentate ‐Coordinating Ligands Based on Imides, Amides, and Hydrazides: Synthesis and Luminescence Properties

AbstractFive Pt(II) complexes are described in which the metal ion is bound to anionic ‐coordinating ligands. The central, deprotonated N atom is derived from an imide Ar−C(=O)−NH−C(=O)−Ar {PtL1–2Cl; Ar=pyridine or pyrimidine}, an amide py−C(=O)−NH−CH2−py {PtL3Cl}, or a hydrazide py−C(=O)−NH−N=CH−py {PtL4Cl}. The imide complexes PtL1–2Cl show no significant emission in solution but are modestly bright green/yellow phosphors in the solid state. PtL3Cl is weakly phosphorescent. PtL4Cl is formed as a mixture of isomers, bound through either the amido or imino nitrogen, the latter converting to the former upon absorption of light. Remarkably, the imino form displays fluorescence in solution, λ0,0=535 nm, whereas the amido shows phosphorescence, λ0,0=624 nm, τ=440 ns. It is highly unusual for two isomeric compounds to display emission from states of different spin multiplicity. The amido‐bound PtL4Cl can act as a bidentate ‐coordinating ligand, demonstrated by the formation of bimetallic complexes with iridium(III) or ruthenium(II).

Metal‐Templated, Tight Loop Conformation of a Cys‐X‐Cys Biomimetic Assembles a Dimanganese Complex

AbstractWith the goal of generating anionic analogues to MN2S2⋅Mn(CO)3Br we introduced metallodithiolate ligands, MN2S22− prepared from the Cys‐X‐Cys biomimetic, ema4− ligand (ema=N,N′‐ethylenebis(mercaptoacetamide); M=NiII, [VIV≡O]2+ and FeIII) to Mn(CO)5Br. An unexpected, remarkably stable dimanganese product, (H2N2(CH2C=O(μ‐S))2)[Mn(CO)3]2 resulted from loss of M originally residing in the N2S24− pocket, replaced by protonation at the amido nitrogens, generating H2ema2−. Accordingly, the ema ligand has switched its coordination mode from an N2S24− cavity holding a single metal, to a binucleating H2ema2− with bridging sulfurs and carboxamide oxygens within Mn‐μ‐S‐CH2‐C‐O, 5‐membered rings. In situ metal‐templating by zinc ions gives quantitative yields of the Mn2 product. By computational studies we compared the conformations of “linear” ema4− to ema4− frozen in the “tight‐loop” around single metals, and to the “looser” fold possible for H2ema2− that is the optimal arrangement for binucleation. XRD molecular structures show extensive H‐bonding at the amido‐nitrogen protons in the solid state.

Metal-Templated, Tight Loop Conformation of a Cys-X-Cys Biomimetic Assembles a Dimanganese Complex.

With the goal of generating anionic analogues to MN2 S2 ⋅Mn(CO)3 Br we introduced metallodithiolate ligands, MN2 S22- prepared from the Cys-X-Cys biomimetic, ema4- ligand (ema=N,N'-ethylenebis(mercaptoacetamide); M=NiII , [VIV ≡O]2+ and FeIII ) to Mn(CO)5 Br. An unexpected, remarkably stable dimanganese product, (H2 N2 (CH2 C=O(μ-S))2 )[Mn(CO)3 ]2 resulted from loss of M originally residing in the N2 S24- pocket, replaced by protonation at the amido nitrogens, generating H2 ema2- . Accordingly, the ema ligand has switched its coordination mode from an N2 S24- cavity holding a single metal, to a binucleating H2 ema2- with bridging sulfurs and carboxamide oxygens within Mn-μ-S-CH2 -C-O, 5-membered rings. In situ metal-templating by zinc ions gives quantitative yields of the Mn2 product. By computational studies we compared the conformations of "linear" ema4- to ema4- frozen in the "tight-loop" around single metals, and to the "looser" fold possible for H2 ema2- that is the optimal arrangement for binucleation. XRD molecular structures show extensive H-bonding at the amido-nitrogen protons in the solid state.

Iron(II) coordination complexes with panchromatic absorption and nanosecond charge-transfer excited state lifetimes.

Replacing current benchmark rare-element photosensitizers with ones based on abundant and low-cost metals such as iron would help facilitate the large-scale implementation of solar energy conversion. To do so, the ability to extend the lifetimes of photogenerated excited states of iron complexes is critical. Here, we present a sensitizer design in which iron(II) centres are supported by frameworks containing benzannulated phenanthridine and quinoline heterocycles paired with amido donors. These complexes exhibit panchromatic absorption and nanosecond charge-transfer excited state lifetimes, enabled by the combination of vacant, energetically accessible heterocycle-based acceptor orbitals and occupied molecular orbitals destabilized by strong mixing between amido nitrogen atoms and iron. This finding shows how ligand design can extend metal-to-ligand charge-transfer-type excited state lifetimes of iron(II) complexes into the nanosecond regime and expand the range of potential applications for iron-based photosensitizers.

Direct Synthesis of Vicinal Tricarbonyl Amides by Coupling of α-Oxo Acid Chlorides with Carbamoylsilanes

A convenient synthetic method for vicinal tricarbonyl amides by the cross-coupling reaction of α-oxo acid chlorides with carbamoylsilanes is developed. The reaction tolerates a broad range of substituents on the amido nitrogen of carbamoylsilanes, and directly affords good yields of vicinal tricarbonyl amides under mild conditions without use of oxidants. The reaction of carbamoylsilanes with oxalyl chloride has also been explored, and is accompanied by decarbonylation to give vicinal tricarbonyl amides.

Protonation Studies of Molybdenum(VI) Nitride Complexes That Contain the [2,6-(ArNCH2)2NC5H3]2- Ligand (Ar = 2,6-Diisopropylphenyl).

[Ar2N3]Mo(N)(O- t-Bu) (1), which contains the conformationally rigid pyridine-based diamido ligand [2,6-(ArNCH2)2NC5H3]2- (Ar = 2,6-diisopropylphenyl), is a catalyst for the reduction of dinitrogen with protons and electrons. Various acids have been added in order to explore where and how the first proton adds to the complex. The addition of adamantol to 1 produces a five-coordinate bis(adamantoxide), [HAr2N3]Mo(N)(OAd)2 (2a), in which one of the amido nitrogens in the ligand has been protonated and the resulting aniline nitrogen in the [HAr2N3]- ligand is not bound to the metal. The addition of [Ph2NH2][OTf] to 1 produces {[HAr2N3]Mo(N)(O- t-Bu)}(OTf) (3), in which an amido nitrogen has been protonated, but the aniline in the [HAr2N3]- ligand remains bound to the metal. Last, the addition of (2,6-lutidinium)BArF4 (BArF4 = {B(3,5-(CF3)2C6H3)4}-) to 1 yields {[Ar2N3]Mo(N)(LutH)(O- t-Bu)}BArF4, in which LutH+ is hydrogen-bonded to the nitride in the solid state and in dichloromethane with Keq = 412 ± 94 and Δ G = -3.6 ± 0.8 kcal at 22 °C. A similar hydrogen-bonded adduct was formed through the addition of (2-methylpyridinium)BArF4 to 1, but the addition of (pyridinium)BArF4 to 1 leads to the formation of (inter alia) {[HAr2N3]Mo(N)(O- t-Bu)}(BArF4), in which the amide nitrogen has been protonated. The addition of cobaltocene to 3 or {[Ar2N3]Mo(N)(LutH)(O- t-Bu)}(BArF4) leads only to the re-formation of 1. X-ray structural studies were carried out on 2a, 3, and {[Ar2N3]Mo(N)(LutH)(O- t-Bu)}(BArF4).

Tetradentate amido azo Schiff base Cu(II), Ni(II) and Pd(II) complexes: Synthesis, characterization, spectral properties, and applications to catalysis in C–C coupling and oxidation reaction

New Schiff base ligands (H2L1 &H2L2) were synthesized by the reaction of salicylaldehyde with (2-((2-aminophenyl)diazenyl)-N-alkylaniline), and were used for the preparation of complexes with Cu(II), Ni(II) and Pd(II) metal ions. The structural features of the synthesized compounds were examined by UV–Vis, IR and 1H NMR spectroscopy. The crystal structures of Schiff base (H2L1) and two metal complexes Cu(L1) and Ni(L2) were determined by single crystal X-ray diffraction. The studies revealed that the synthesized Schiff bases existed as tetradentate (N,N,N,O) ligands and bonded to the metal ions through the donor atoms of the amido nitrogen, azo nitrogen, azomethine nitrogen and phenolic oxygen atoms. The redox property of Cu(L1) and Ni(L1) and emission behavior of ligand H2L1 and complexes Cu(L1) and Ni(L1) were examined. The complex Cu(L1) shows excellent catalytic activity towards oxidation of benzyl alcohol to benzyldehyde (under solvent-free condition) using H2O2 as the oxidant. Complex Pd(L1) acts as highly efficient catalyst in the Suzuki–Miyaura cross-coupling reaction of various aryl halides with phenyl boronic acid to produce the corresponding biaryls with high yields under mild reaction conditions. Both the catalysts Cu(L1) and Pd(L1) were easily recovered by simple chromatographic separation and reused for next catalytic cycle.

Molybdenum Complexes that Contain a Calix[6]azacryptand Ligand as Catalysts for Reduction of N2 to Ammonia.

[CAC(OMe)6]Mo(N) (3, where [CAC]3- is a calix[6]azacryptand ligand derived from a [6]calixarene) has been prepared in a reaction between Li3[CAC(OMe)6] and ( t-BuO)3Mo(N). An X-ray structural study showed 3 to have a structure similar to that of [HIPTN3N]Mo(N) (where [HIPTN3N]3- is [(3,5-(2,4,6-triisopropylphenyl)2C6H3NCH2CH2)3N]3-). The relatively rigid [CAC(OMe)6]3- ligand in 3 forms a bowl-shaped cavity defined by a 24-atom macrocyclic ring. The Mo-Namido-Cipso angles are ∼8° smaller in 3 than they are in [HIPTN3N]Mo(N). Methoxides on the three linking units point into the cavity above the nitride in 3, whereas the three methoxides on phenyl rings attached to the amido nitrogen atoms point away from the cavity. An analogous [CAC(OMe)3(H)3]Mo(N) complex (9) was prepared in which the three methoxides pointing into the cavity in 3 have been replaced by protons. Its structure differs little from that of 3. The nitride could be protonated in 3 to give {[CAC(OMe)6]Mo(NH)}+, which could be reduced (reversibly) to [CAC(OMe)6]Mo(NH). Catalytic reduction of molecular nitrogen under a variety of conditions with either Ph2NH2OTf or HBArf (BArf- = {B[3,5(CF3)2C5H3]4}-) as the acid and a Co metallocene or KC8 as the reducing agent between -78 and 22 °C in diethyl ether shows that 1.20-1.34 equivalents of ammonia are formed starting with either [CAC(OMe)6]Mo(N) (50% 15N) or [CAC(OMe)3(H)3]Mo(N) (50% 15N).

Synthesis, structure, and characterization of molybdenum(VI) imido complexes with N-salicylidene-2-aminothiophenol

The di-imido complex Mo(NAr)2Cl2(dme) (dme = 1,2-dimethoxyethane; Ar = 2,6-diisopropylphenyl) reacts with the sulfur ligand N-salicylidene-2-aminothiophenol (smaH2) in methanol in the presence of two equivalents of triethylamine to form Mo(NAr)2sma (1). The structure of this molybdenum(VI) complex has been determined by X-ray crystallography. The coordination sphere of the Mo center is approximately a trigonal bipyramid. The angles of the imido linkages (Mo–N–C) are 175° and 147°. The tridentate sma ligand binds with the imine nitrogen in the axial position trans to the 175° imido linkage. 1 can be reacted with bidentate aromatic ligands to form six-coordinate complexes of the type Mo(ArN)(sma)(L) (L = catecholate, 2; 2-mercaptophenolate, 3, 1,2-benzenedithiolate, 4; 2-amidophenolate, 5; 3-amidonaphtholate, 6; 1,2-amidonaphtholate, 7; 2-amidothiophenolate, 8). The structures of compounds 2–7 have been determined by X-ray crystallography. In 2, 3, and 4 the bidentate ligand, L, binds in two equatorial positions cis to the imido linkage. In 5, 6 and 7 L binds in an axial and an equatorial position where the amido nitrogen occupies the equatorial position. All complexes have been characterized by 1H NMR spectroscopy and cyclic voltammetry. Compounds 2, 3, and 4 can be reversibly reduced with one electron to EPR-active Mo(V) complexes. The EPR spectrum of 4 shows superhyperfine splitting from the imido nitrogen. This indicates that the unpaired electron is located in the dz2 orbital that interacts with the imido nitrogen and the imine nitrogen of the sma ligand and is not influenced by the bidentate aromatic ligand which binds in two equatorial positions. This explains the similar redox potentials of the three complexes. In complexes 5–8 the reduction is not reversible and the potential is influenced by the atom of the bidentate aromatic ligand trans to the imido group.

Synthesis of new drug model has an effective antimicrobial and antitumors by combination of cephalosporin antibiotic drug with silver(I) ion in nano scale range: Chemical, physical and biological studies

The present study describes the synthesis, structural characterization and antimicrobial assays of four silver(I) complexes with four generations of the cephalosporin drugs cefradine (Cef-1; 1st), cefoxitin sodium (Cef-2; 2nd), cefotaxime sodium (Cef-3; 3rd) and cefepime hydrochloride (Cef-4; 4th). The microanalytical analyses led to 1:1 (Ag+/ligand) compositions, suggesting the speculated general formulas [Ag2(Cefn)2] where n=1st, 2nd, 3rd, or 4th. Infrared and proton NMR spectroscopic measurements indicated all Cefn ligands coordination to Ag+ through the oxygen atoms of the carbonyl β-lactam and carboxylate groups, whereas oxygen atom of amido (NH-CO) group and nitrogen atom of amino group of does not participate in the chelation with the silver metal ions. The proposed coordination modes shows the bridging case of coordination, that the two Ag+ ions linked bridge between the oxygen atom of the carbonyl β-lactam and carboxylate groups of two Cefn ligands. Antimicrobial assessments indicated that silver(I) complexes are more active against some kind of bacteria (Gram-positive bacteria, Staphylococcus aureus (MSSA 22) and Bacillus subtilis (ATCC 6051), and two Gram-negative bacteria, Escherichia coli (K 12) and Pseudomonas aeruginosa (MTCC 2488) than the parents Cefn drugs. The nature of the synthesized silver(I) nanoparticles AgNPs compounds were analyzed using UV–Vis spectrophotometer, solid X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM). The particle size of AgNPs compounds were within 113–173nm nano scale range.

Synthesis, characterization and DNA binding investigations on 1D polymeric copper(II) complexes of 1-amidino-O-alkylurea (alkyl = methyl, ethyl or propyl) having both dicyanamido and chloro bridges

Three new copper(II) complexes, [(CuL)2Cl{N(CN)2}3]n, where L = 1-amidino-O-methylurea (1), 1-amidino-O-ethylurea (2), or 1-amidino-O-propylurea (3), have been synthesized and characterized. The single crystal X-ray structure of 2 and X-ray powder diffraction analysis on 1 and 3 show that they crystallize in the monoclinic system. The neutral dinuclear entity of 2 contains a crystallographic 2-fold axis passing through the amido nitrogen of a bridging dicyanamido ligand. The dinuclear units are bridged by weak Cu … Cl interactions through the axial position of both copper ions to form a 1D polymer. The interaction of 1–3 with calf-thymus DNA (CT-DNA) has been explored by using absorption, emission, thermal denaturation, cyclic voltammetric studies, and viscosity experiments. The complexes bind to CT-DNA by non-intercalative mode and the order of binding ability is 1 > 2 > 3.

A Triflamide‐Tethered N‐Heterocyclic Carbene–Rhodium(I) Catalyst for Hydroalkoxylation Reactions: Ligand‐Promoted Nucleophilic Activation of Alcohols

AbstractA triflamide‐tethered N‐heterocyclic carbene (NHC)‐bound RhI dicarbonyl catalyst was highly effective for both intermolecular hydroalkoxylation and intramolecular heteroannulation reactions. The involvement of both the amido nitrogen and triflato oxygen atoms of the triflamide functionality for alcohol activation and 1,2‐hydrogen shift, respectively, was proposed.

Reactions of Neutral Cobalt(II) Complexes of a Dianionic Tetrapodal Pentadentate Ligand: Cobalt(III) Amides from Imido Radicals.

Neutral cobalt(II) complexes of the dianionic tetrapodal pentadentate ligand B2Pz4Py, in which borate linkers supply the anionic charges, are reported. Both the six-coordinate THF adduct 1-THF and the five-coordinate THF-free complex 1 are in a high-spin S = 3/2 configuration in the ground state and have been structurally characterized by X-ray crystallography. These two Co(II) starting materials react rapidly with aryl azides of moderate steric bulk. The thermodynamic products of these reactions are low-spin, diamagnetic, Co(III) amido complexes that are either monomeric, when an external hydrogen atom source such as 1,4-cyclohexadiene is present, or dimeric products formed via C-C coupling of the azide aryl group and internal transfer of H• to the nitrogen. These products are fully characterized and are rare examples of octahedral Co amido compounds; structural determinations reveal significant pyramidalization of the amido nitrogens due to π-π repulsion wherein the amido ligand is primarily a σ donor. The amido products arise from highly reactive Co(III) imido radical intermediates that are the kinetic products of the reactions of 1 or 1-THF with the azide reagents. The imido radicals can be detected by X-band EPR spectroscopy and have been probed by density functional theory computations, which indicate that this doublet species is characterized by a high degree of spin localization on the imido ligand, accounting for the reactivity with hydrogen atom sources and dimerization chemistry observed. The high coordination number and the electron-rich nature of the dianionic B2Pz4Py ligand framework render the imido ligand formed highly reactive.

Translocator protein ligands based on N-methyl-(quinolin-4-yl)oxypropanamides with properties suitable for PET radioligand development

Modifications to an N-methyl-(quinolin-4-yl)oxypropanamide scaffold were explored to discover leads for developing new radioligands for PET imaging of brain TSPO (translocator protein), a biomarker of neuroinflammation. Whereas contraction of the quinolinyl portion of the scaffold or cyclization of the tertiary amido group abolished high TSPO affinity, insertion of an extra nitrogen atom into the 2-arylquinolinyl portion was effective in retaining sub-nanomolar affinity for rat TSPO, while also decreasing lipophilicity to within the moderate range deemed preferable for a PET radioligand. Replacement of a phenyl group on the amido nitrogen with an isopropyl group was similarly effective. Among others, compound 20 (N-methyl-N-phenyl-2-[2-(pyridin-2-yl)-1,8-naphthyridin-4-yloxy]propanamide) appears especially appealing for PET radioligand development, based on high selectivity and high affinity (Ki = 0.5 nM) for rat TSPO, moderate lipophilicity (logD = 2.48), and demonstrated amenability to labeling with carbon-11.