Ortho Substituents Research Articles

Influence of ortho group in rhodamine B hydrazide based Schiff base for selective recognition of Cu2+ and Fe3+ ions: A mechanistic approach by DFT and colorimetric studies

Herein we have implemented a computational approach in designing sensor molecules for the selective recognition of Cu2+ and Fe3+ ions. Seven rhodamine B hydrazide-based Schiff base derivatives were designed and analysed their chemosensing properties against Cu2+ and Fe3+ ions in ethanol solution theoretically. The theoretical calculations revealed that the selective recognition of Cu2+ and Fe3+ ions takes place via spirolactam ring-opening and there is a pivotal role of ortho substituents and N-heteroatoms. The two best chemosensors were synthesised and used for the detection of Cu2+ and Fe3+ ions by colorimetric methods.

The relative favorability of placing substituents ortho or para in the cationic intermediate for electrophilic aromatic substitution

AbstractRegioselectivity in electrophilic aromatic substitution (EAS) is partly governed by how well a preexisting substituent stabilizes or destabilizes the cationic intermediate formed by addition of an electrophile. Such intermediates were modeled computationally (G4) by adding a proton ortho, meta, or para to an existing substituent on a benzene ring. The effect of a meta substituent depends on the electronic character, as measured by the Hammett substituent constant σm or, better yet, σ+m. Similarly, the effect of a para or ortho substituent correlates with σ+p (= σ+). However, the influence of a substituent at the para position is 10% stronger than at the ortho position. Frontier molecular orbital arguments rationalize this observation. Consequently, the ortho:para product ratio in EAS is expected to depend, at least in part, on σ+p, with greater electron‐donating character associated with a greater preference for para over ortho. The ortho‐substituted cationic intermediate can even be favored over both meta and para if the electron‐withdrawing character is sufficient to favor ortho over para but insufficient to favor meta over either. This phenomenon is observed to occur in at least some cases when the quantity σ+p–σm falls between –0.5 and 0.

Lignin-based benzoxazines: A tunable key-precursor for the design of hydrophobic coatings, fire resistant materials and catalyst-free vitrimers

The meaningful concept of circular economy has prompted the scientific community to re-think the design of materials. In this work, lignin-based benzoxazines (LBZs) thermosets with tuneable properties were synthesized in agreement with the principles of Green Chemistry, following a straightforward two-step synthetic route. The reactivity of a soda lignin was enhanced by its esterification with phloretic acid, a naturally occurring phenolic acid. Thereafter, the resulting structure enriched in phenolic rings with no ortho substituents, was used to prepare LBZs precursors with a bio-based primary amine via a Mannich-like ring-closure reaction. The structure and properties of each LBZ precursor were confirmed by multiple NMR techniques, Fourier transform infrared spectroscopy, elemental analysis, gel permeation chromatography, differential scanning calorimetry, rheology, and solubility assays. Lignin-based polybenzoxazine with high lignin mass fraction (between 46 and 66 wt.%) were obtained following curing via a vacuum compression molding manufacture process. Lignin-based thermosets exhibit a single-phase confirmed by X-ray computed tomography analysis, a Tg ranging from 136 to 197 °C, and storage moduli from 0.5 to 3.1 GPa. The features of each lignin-based precursor were tuned depending on the structure of the bio-based primary amine used to close the oxazine ring. Stearylamine confers good processability and yields hydrophobic coatings with a water contact angle reaching 91°. Furfurylamine-based LBZs generate high-Tg (197 °C) and fire-resistant materials with a peak of heat release rate of no>47 W.g−1. Finally, ethanolamine produces lignin-based thermosets capable of internally catalysed bond exchange via transesterification, providing vitrimeric properties such as fast stress relaxation (τ*200 °C = 233 s) and a complete circularity.

From Gas Phase Observations to Solid State Reality: The Identification and Isolation of Trinuclear Salicylaldoximato Copper Complexes.

Conditions have been identified in which phenolic aldoximes and ketoximes of the types used in commercial solvent extraction processes can be doubly deprotonated and generate polynuclear Cu complexes with lower extractant:Cu molar ratios than those found in commercial operations. Electrospray mass spectrometry has provided an insight into the solution speciation in extraction experiments and has identified conditions to allow isolation and characterization of polynuclear Cu-complexes. Elevation of pH is effective in enhancing the formation of trinuclear complexes containing planar {Cu3-μ3-O}4+ or {Cu3-μ3-OH}5+ units. DFT calculations suggest that such trinuclear complexes are more stable than other polynuclear species. Solid structures of complexes formed by a salicylaldoxime with a piperidino substituent ortho to the phenolic OH group (L9H2) contain two trinuclear units in a supramolecular assembly, {[Cu3OH(L9H)3(ClO4)](ClO4)} 2, formed by H-bonding between the central {Cu3-μ3-OH}5+ units and oxygen atoms in the ligands of an adjacent complex. Whilst the lower ligand:Cu molar ratios provide more efficient Cu-loading in solvent extraction processes, the requirement to raise the pH of the aqueous phase to achieve this will make it impractical in most commercial operations because extraction will be accompanied by the precipitation (as oxyhydroxides) of Fe(III) which is present in significant quantities in feed solutions generated by acid leaching of most Cu ores.

Inverse molecular design of alkoxides and phenoxides for aqueous direct air capture of CO2

Aqueous direct air capture (DAC) is a key technology toward a carbon negative infrastructure. Developing sorbent molecules with water and oxygen tolerance and high CO2 binding capacity is therefore highly desired. We analyze the CO2 absorption chemistries on amines, alkoxides, and phenoxides with density functional theory calculations, and perform inverse molecular design of the optimal sorbent. The alkoxides and phenoxides are found to be more suitable for aqueous DAC than amines thanks to their water tolerance (lower pKa prevents protonation by water) and capture stoichiometry of 1:1 (2:1 for amines). All three molecular systems are found to generally obey the same linear scaling relationship (LSR) between [Formula: see text] and [Formula: see text], since both CO2 and proton are bonded to the nucleophilic (alkoxy or amine) binding site through a majorly [Formula: see text] bonding orbital. Several high-performance alkoxides are proposed from the computational screening. Phenoxides have comparatively poorer correlation between [Formula: see text] and [Formula: see text], showing promise for optimization. We apply a genetic algorithm to search the chemical space of substituted phenoxides for the optimal sorbent. Several promising off-LSR candidates are discovered. The most promising one features bulky ortho substituents forcing the CO2 adduct into a perpendicular configuration with respect to the aromatic ring. In this configuration, the phenoxide binds CO2 and a proton using different molecular orbitals, thereby decoupling the [Formula: see text] and [Formula: see text]. The [Formula: see text] trend and off-LSR behaviors are then confirmed by experiments, validating the inverse molecular design framework. This work not only extensively studies the chemistry of the aqueous DAC, but also presents a transferrable computational workflow for understanding and optimization of other functional molecules.

Weakly Bound Dimer of a Diaryloxygermylene Derived from a tBuPh2Si-Substituted 2,2′-Methylenediphenol

Novel diaryloxygermylenes have been prepared by the reaction of Lappert’s germylene, Ge[N(SiMe3)2]2, with 2,2′-methylenediphenols bearing different substituents. The bulkiness of the substituents on the ortho positions of the phenolic oxygen (6 and 6′ positions) affects the structure of the products both in the solid-state and in solution. When the ortho substituents are SitBuPh2, the diaryloxygemylene crystalizes as a weakly bound dimer with intermolecular Ge…O distances of ca. 3.0 Å and exists as a monomer in solution. In contrast, the germylene with SiMePh2 groups as the ortho substituents form a tightly bound dimer featuring a Ge2O2 rhombus with cis-oriented terminal aryloxy groups in the crystalline state, which is confirmed to be maintained in solution through the VT (variable-temperature)-1H NMR studies. To the best of our knowledge, the former dimeric structure is unprecedented in the family of dioxytetrylenes.

Multicomponent synthesis of novel dihydropyrano-dioxine fused-bicyclic systems as a potentially new class of heterocyclic atropisomers

A new series of dihydropyrano-dioxine products were synthesized via one-pot combination of 2,2-dimethyl-1,3-dioxan-5-one with aromatic aldehydes and malononitrile. The first step occurs rapidly in an aqueous alcoholic medium at reflux, followed by nucleophilic addition of malononitrile to the olefinic site of the intermediate and iodine induced oxidation to the final products, which directly precipitate in the vessel, avoiding time consuming and expensive chromatographic separations. The structure of the products was elucidated based on their NMR data and verified by X-ray crystallography. In the case of α-substituted derivatives, rotational barrier caused by the bulk of the ortho substituent led to the formation of atropisomeric products. To study this aspect, molecular geometry of 4 g was optimized by ChemDraw professional 20 and then MM2 calculation was performed.

Schistosomicidal evaluation of synthesized bromo and nitro chalcone derivatives

Chalcones are compounds associated to several biological activities. The modification of chemical structures is one of the most widely used tool in the pharmaceutical industry to obtain new drugs. In this study, we synthetized chalcones with nitro and bromo substituents in different positions in the aromatic rings. NMR spectroscopy was used for characterization. Simultaneously, a conformational study of the compounds was carried out employing theoretical calculations. Furthermore, the schistosomicidal in vitro effect of bromo and nitro chalcone substituents on adult Schistosoma mansoni was investigated. The results showed that most chalcones have a conformational preference for s-cis geometry, which is favored by the conjugative effect of electronic delocalization. However, chalcones with ortho substituents dissipate greater stabilization of s-trans conformations, possibly for favoring surfaces with weak interactions such as Van der Waals. In addition, a significant effect of chalcones on female and male S. mansoni was observed. All samples evaluated reduced the motor activity of worms, caused mortality in male and female worms, and resulted in morphological alterations in a concentration- dependent manner (25–200 μg/mL) in a period of 6–24 h of incubation. Additionally, chalcones influenced the separation of couple worms and suppressed egg production at sublethal concentrations. Our results demonstrated that chalcones present potential to be used as schistosomicidal drugs, contributing to the clarification of the relation between the molecule conformation and the associated biological effects.

Remote steric control for undirected meta-selective C-H activation of arenes.

Regioselective functionalization of arenes remains a challenging problem in organic synthesis. Steric interactions are often used to block sites adjacent to a given substituent, but they do not distinguish the remaining remote sites. We report a strategy based on remote steric control, whereby a roof-like ligand protects the distant para site in addition to the ortho sites, and thereby enables selective activation of meta carbon-hydrogen (C-H) bonds in the absence of ortho or para substituents. We demonstrate this concept for iridium-catalyzed meta-selective borylation of various monosubstituted arenes, including complex drug molecules. This strategy has the potential to expand the toolbox of C-H bond functionalization to previously nondifferentiable reaction sites.

Effects of the halogenido ligands on the Kumada-coupling catalytic activity of [Ni{ t BuN(PPh2)2-κ2P}X2], X = Cl, Br, I, complexes.

Novel nickel(ii) complexes bearing (tbutyl)bis(diphenylphosphanyl)amine and different halogenido ligands, [Ni(P,P)X2] = [Ni{tBuN(PPh2)2-κ2P}X2], (X = Cl, Br, I) are prepared, characterized by IR and NMR spectroscopy, mass spectrometry and X-ray crystallography, and tested as catalysts in the Kumada cross-coupling reaction of model substituted iodobenzenes and p-tolylmagnesium bromide. The data obtained together with DFT calculations indicate that these new catalysts operate in the Ni(i)–Ni(iii) mode. The highest catalytic activity and selectivity are exhibited by [Ni(P,P)Cl2], which is most easily reduced by the used Grignard reagent to the Ni(i) state. This process is much more energy demanding in the case of the bromido and iodido complexes, causing the appearance of the induction period. [Ni(P,P)Cl2] is also very active in the cross-couplings of substrates with iodine atoms sterically shielded by ortho substituents. The data obtained are in good accordance with the described positive effect of the increased electron-releasing power of N-substituents R′ on the overall catalytic performance of [Ni{R′N(PPh2)2-κ2P}X2] complexes.

Cationic [6]Helicenes: Tuning (Chir)Optical Properties up to the Near Infra-Red

The intramolecular condensation of ortho substituents of triaryl carbenium ions can lead to the formation of cationic helicenes. These chiral and configurationally stable molecules exhibit extended optical properties reminiscent of their parent methylium ions. Among them, cationic [6]helicenes are particularly interesting as orthogonal late-stage functionalization strategies allow the introduction of a variety of auxochromes with different regiochemistry. Intense chiroptical properties can thus be tailored in the far red and up to the near infra-red (NIR) spectral windows. A wealth of applications can be foreseen, in particular in material sciences.

Atroposelective construction of axially chiral enamides via N-allylic alkylation.

Herein, we report the catalytic asymmetric synthesis of a unique family of axially chiral enamides in good yields with excellent enantioselectivities under mild conditions. These new axially chiral compounds feature a flexible skeleton and a high degree of rotational freedom, which raises difficulties for enantiocontrol. A mechanism model is proposed to interpret the stereoselectivity, in which both the steric difference of the ortho substituents and the π-π stacking interaction may contribute to the stereo-control.

Energy barriers to rotation in axially chiral quinazoline-4-ones

Axially chiral 2-thioxo-3-(o-aryl)-quinazolin-4-ones and 2-(benzylthio)-3-(o-aryl)-quinazolin-4-ones were synthesized and their energy barriers to rotation about the N3-Caryl bond were determined by thermal racemization of the separated enantiomers. The rotational barriers were found to range from 112.7 to 140.8 kJ/mol, depending on size of the ortho substituent and to increase linearly with the size of the van der Waals radii of the ortho-halogen substituents. Although the isolation of the enantiomers of the N–C axially chiral compounds bearing an ortho-fluoro substituent are rare because of small size of fluorine atom, we found that the rotational barriers of quinazolin-4-ones bearing an ortho-fluoro group are high enough allowing the isolation of enantiomers.

Structurally Diverse Synthesis of Five-, Six-, and Seven-Membered Benzosultams through Electrochemical Cyclization

We have developed a metal- and oxidant-free approach to structurally diverse synthesis of benzosultams from aryl sulfonamides through an electrochemical cyclization. Upon variation of the ortho substituent on aryl sulfonamides, five-, six-, and seven-membered benzosultams were efficiently assembled in an atom- and resource-economic manner. The generality of the process is demonstrated by the formation of five- to seven-membered cyclic products from 42 substrates bearing substituents with different electronic effects and steric hindrance.

Synthesis, structures and luminescence properties of N^C^N-coordinated platinum(II) complexes based on an anthracene core: A red shift and a twist

1,8-Bis(2-pyridyl)anthracene HL2 is shown to act as a tridentate, N^C^N-coordinating ligand to platinum(II), undergoing metallation at position 9 of the anthracene. The structures of Pt(N^C^N-L2)Cl and of HL2 have been determined by X-ray diffraction. The complex features two 6-membered chelate rings and an N-Pt-N bite angle of 178.16(7)°, close to the “ideal” value of 180°. The attainment of this angle necessitates not only a twisting of the pyridyl rings relative to the anthracene, but also a remarkable twisting distortion of the anthracene unit itself. The complex is isomeric with the previously reported Pt(d8qb)Cl {d8qb = 1,3-di(8-quinolyl)benzene}. A new derivative of the latter has been prepared, PtL3Cl, featuring methyl substituents in the central benzene ring ortho to the quinolines. Like PtL2Cl, its structure shows twisting of the coordinated heterocycles relative to the plane of the central aromatic ring. The Pt(II) complex PtL1Cl of a related N^C^N-coordinating ligand featuring extended conjugation, benzo[1,2-h: 5,4 = h’]diquinoline HL1, has also been prepared following a previously described procedure. PtL1Cl is brightly phosphorescent in deoxygenated solution at ambient temperature, in the red region of the spectrum. The impressive photoluminescence quantum yield of 0.30 and long emission lifetime of 38 μs are indicative of a rigid structure with little excited state distortion. In contrast, PtL2Cl shows no detectable emission, probably due to the distorted nature of the structure leading to rapid non-radiative decay of the excited state. This result contrasts with the weak red emission displayed by the isomeric Pt(d8qb)Cl and its dimethylated derivative PtL3Cl.

Recurring Real-Time Monitoring of Inflammations in Living Mice with a Chemiluminescent Probe for Hypochlorous Acid

Recurring Real-Time Monitoring of Inflammations in Living Mice with a Chemiluminescent Probe for Hypochlorous Acid

Bis(2-nitrophenyl) selenide, bis(2-aminophenyl) selenide and bis(2-aminophenyl) telluride: structural and theoretical analysis.

Three organoselenium and organotellurium compounds containing ortho substitutents, namely, bis(2-nitrophenyl) selenide, C12H8N2O4Se, 2, bis(2-aminophenyl) selenide, C12H12N2Se, 3, and bis(2-aminophenyl) telluride, C12H12N2Te, 7, have been investigated by both structural and theoretical methods. In the structures of all three compounds, there are intramolecular contacts between both Se and Te with the ortho substituents. In the case of 2, this is achieved by rotation of the nitro group from the arene plane. For 3, both amino groups exhibit pyramidal geometry and are involved in intramolecular N-H...Se interactions, with one also participating in intermolecular N-H...N hydrogen bonding. While 3 and 7 are structurally similar, there are some significant differences. In addition to both intramolecular N-H...Te interactions and intermolecular N-H...N hydrogen bonding, 7 also exhibits intramolecular N-H...N hydrogen bonding. In the packing of these molecules, for 2, there are weak intermolecular C-H...O contacts and these, along with the O...N interactions mentioned above, link the molecules into a three-dimensional array. For 3, in addition to the N-H...N and N-H...Se interactions, there are also weak intermolecular C-H...Se interactions, which also link the molecules into a three-dimensional array. On the other hand, 7 shows intermolecular N-H...N interactions linking the molecules into R22(16) centrosymmetric dimers. In the theoretical studies, for compound 2, AIM (atoms in molecules) analysis revealed critical points in the Se...O interactions with values of 0.017 and 0.026 a.u. These values are suggestive of weak interactions present between Se and O atoms. For 3 and 7, the molecular structures displayed intramolecular, as well as intermolecular, hydrogen-bond interactions of the N-H...N type. The strength of this hydrogen-bond interaction was calculated by AIM analysis. Here, the intermolecular (N-H...N) hydrogen bond is stronger than the intramolecular hydrogen bond. This was confirmed by the electron densities for 3 and 7 [ρ(r)= 0.015 and 0.011, respectively].

A Phosphine-Mediated Dearomative Skeletal Rearrangement of Dianiline Squaraine Dyes.

A phosphorus(III)-mediated dearomatization of ortho-substituted dianiline squaraine dyes results in an unusual skeletal rearrangement to provide exotic, highly conjugated benzofuranone and oxindole scaffolds bearing a C3 side chain comprised of a linear conflagration of an enol, a phosphorus ylide, and 2,4-disubstituted aniline. Employing experimental and computational analysis, a mechanistic evaluation revealed a striking dependence on the acidity of the aniline ortho substituent. Notably, the rearrangement adducts underwent rapid and complete reversion to the parent squaraine in the presence of a Brønsted acid.

Ni-catalyzed enantioselective [2 + 2 + 2] cycloaddition of malononitriles with alkynes

Summary Efficient strategies to assemble enantioenriched pyridine derivatives are highly important, given their significance in both synthetic and medicinal chemistry. Here, we report an enantioselective nickel-catalyzed intermolecular [2 + 2 + 2] cycloaddition of alkyne-tethered malononitriles with alkynes for the synthesis of densely substituted pyridines. The α-all-carbon quaternary center adjacent to pyridine is introduced by desymmetrizing the two cyano groups of disubstituted malononitriles. Notably, terminal alkynes are also tolerated with good regioselectivity to afford tetrasubstituted pyridines. Zinc halide is essential to enable the occurrence of the transformation by promoting the hetero-cyclometallation step. The reaction uses bio-renewable 2-MeTHF as the solvent and features mild reaction conditions, good functional group compatibilities, and enantioselectivities. This study offers a straightforward approach to the valuable enantioenriched heteroarenes from feedstock chemicals by forming three bonds and one quaternary stereocenter simultaneously in a single reaction step.

Synthesis of New Dendritic Titanium Catalysts and Catalytic Ethylene Polymerization.

The 1.0G dendrimer polyamidoamine (PAMAM), 3,5-dichlorosalicylaldehyde, and TiCl4·2THF were used as synthetic materials, and the dendritic salicylaldehyde imide ligand with substituent hindrance and its titanium catalyst were synthesized by the condensation reaction of Schiff base. The structure of the synthesized products was characterized by infrared spectroscopy, nuclear magnetic resonance hydrogen spectroscopy, ultraviolet spectroscopy, electrospray mass spectrometry, and inductively coupled plasma-mass spectrometry. Activated methylaluminoxane (MAO) was used as a catalyst precursor for ethylene polymerization in the process of ethylene catalytic. The effects of ethylene polymerization were studied in terms of the Al/Ti molar ratio, reaction time, reaction temperature, polymerization pressure, and ligand structure of the catalyst. The results show good catalytic performance (70.48 kg PE/mol Ti·h) for ethylene polymerization because of the existence of ortho substituent hindrance on the salicylaldehyde skeleton. Furthermore, high-temperature gel permeation chromatography (GPC)-IR, differential scanning calorimetry (DSC), and torque rheometer were used to characterize the microstructure, thermal properties, and viscoelastic state of the polyethylene samples obtained. The results showed that the product was ultrahigh-molecular-weight polyethylene.