Naphthalene-1,2,3-dithiazolyl and its selenium-containing variants

Synthetic routes to salts of the 3H-naphtho[1,2-d][1,2,3]dithiazolylium cation and its three selenium-containing variants (SSeN, SeSN, and SeSeN) are described. The most efficient and general method involves the intermediacy of bis-acetylated aminothiolates and aminoselenolates. These reagents react smoothly with sulfur and selenium halides to afford the desired ring closure products. Electrochemical reduction of the four cations indicates that corresponding radicals (SSN, SSeN, SeSN, and SeSeN) are stable in solution. The EPR spectra of all four have been recorded, and experimental spin distributions have been cross-matched with those obtained from DFT calculations. The selenium-containing radicals are thermally unstable at or slightly above room temperature, but the all-sulfur species has been isolated and characterized crystallographically. In the solid state, the radicals are associated into cofacial dimers which are closely linked to other dimers by intermolecular S---S, S---N, and C-H---aromatic ring interactions.     

Pressure enhanced conductivity in bis-1,2,3-thiaselenazolyl dimers

A synthetic sequence to salts of N-alkylated pyridine-bridged 1,2,3-thiaselenazolo-1,2,3-thiaselenazolylium cations [2]+ (R1 = Me, Et; R2 = H) is described. The corresponding radicals 2 (R1 = Me, Et; R2 = H) can be generated from the cations by chemical or electrochemical reduction. Crystals of the two radicals are isostructural and consist of interpenetrating pi-stacked arrays of closed-shell Se-Se sigma-bonded dimers [2]2 laced together with numerous short intermolecular Se- - -Se, Se- - -S, and Se- - -N contacts. Variable-temperature magnetic, conductivity, and near-infrared optical measurements indicate that the bulk materials behave as small band gap semiconductors with room-temperature conductivities sigma(RT) near 10(-6) S cm(-1) and thermal activation energies Ea of 0.32 eV (R1 = Me) and 0.36 eV (R1 = Et). LMTO band structure calculations on both compounds are consistent with this interpretation. The application of external pressure leads to dramatic increases in conductivity; at 4 GPa sigma(RT) reaches a value near 10(-1) S cm(-1) for R1 = Me and 10(-2) S/cm for R1 = Et. The conductivity remains activated for both compounds, but for R1 = Me the activation energy Ea is reduced to near 0.03 eV at 5 GPa, suggestive of a weakly metallic state.     

A pi-stacked 1,2,3-dithiazolyl radical. Preparation and solid state characterization of (Cl2C3NS)(ClC2NS2)

Crystals of (Cl2C3NS)(ClC2NS2), an isothiazolyl-substituted 1,2,3-dithiazolyl radical, consist of evenly spaced, slipped pi-stacks; magnetic and conductivity measurements indicate the material is a Mott insulator with sigma RT = 2 x 10(-7) S cm-1.     

Helicenoid-based bis-1,2,3-triazole tweezer: Synthesis and selective iodide sensing

Abstract

Novel helicenoid based 1,2,3-triazole tweezer 4 was synthesized using a multistep synthetic protocol with high yields from 2,7-Dihydroxynaphtlene 3 as a precursor. This helicenoid-based bis-1,2,3-triazole tweezer 4 selectively causes non-covalent interaction with iodide anion. The UV-vis absorption exhibited enhancement while fluorescence spectra exhibited significant quenching. ¹H NMR titration showed shift of 1,2,3-triazole C-H signal with an increase in iodide concentration. Association constant of 3.818?×?10⁴ M^?1 was recorded for the host interaction with iodide ions. This value of association constant for iodide sensing using 1,2,3-triazole is the best reported so far for hosts with 1,2,3-triazole moiety and suggests that the helicenoid geometry is responsible for this remarkable behavior.     

Synthesis of D-mannitol substituted ether-linked bis-1,2,3-triazoles as models of gemini surfactants

Readily available and low cost D-mannitol was converted into 1,2,5,6-di-O-isopropylidene-D-mannitol (1) in the presence of acetone and zinc chloride. Williamson etherfication of 1 with propargyl bromide afforded the bisalkyne 2 in a very good yield. 1,3-Dipolar cycloaddition of 2 with four different alkyl azides using click conditions gave four novel bistriazoles 3a-d. Removal of the acetal groups of 3a-d afforded the deprotected bistriazoles 4a-d in excellent yields. Products 3 and 4 represent models of gemini surfactants.     

Synthesis,characterization, and antimicrobial activity of new bis-1,2,3-triazol-H-yl-substituted 2-arylbenzimidazoles

New bis-1,2,3-triazol-H-yl-substituted 2-aryl benzimidazoles VIa-VIp were synthesized from O- and N-bis-propargyl substituted 2-arylbenzimidazoles using “click chemistry.” The newly synthesized compounds were characterized by IR, NMR, and mass spectra. These compounds were screened for their activity against bacterial and fungal organisms.     

Regioselective synthesis and antioxidant activity of a novel class of mono and C2-symmetric bis-1,2,3-triazole and acridinedione grafted macromolecules

An expedient regioselectivesynthesis of novel mono, C₂-symmetric bis-triazole and acridinedione bridged macromolecules has been achieved in good yields employing intermolecular Cu(I) catalyzed azide and alkyne click reaction. Synthesis of O-propargyl acridinedione was achieved in three good yielding steps starting from dimedone, while the symmetrical aliphatic and aryl bis-azides were derived from appropriate dibromides in the presence of sodium azide in dry DMF. The synthesized mono and C₂-symmetric bis-macromolecules have been elucidated by ¹H, ¹³C, elemental and mass spectroscopic analysis. The antioxidant activity of synthesized compounds has also been investigated.     

Synthesis of bis-1,2,3-triazolo-bridged unsymmetrical pyrrolobenzodiazepine trimers via ‘click’ chemistry and their DNA-binding studies

New conceivable synthetic approach for the construction of nitrogen-rich 1,2,3-triazolo-pyrrolo[2,1-c][1,4]benzodiazepine (TPBD, 3a-c) trimers has been developed. The first example of a bis-1,2,3-triazolo-bridged unsymmetrical PBD trimer has been successfully synthesized by employing a CuAAC type ‘click’ chemistry protocol. This efficient route generates tri-imine functionality in a single molecule. It has been envisaged that such tri-imine functionalities could bring in efficient interaction with DNA in a sequence-selective manner in the minor groove of duplex DNA. One of the representative analogues 3c has shown improved DNA-binding ability (ΔT_m 23.7 °C) by thermal denaturation studies using CT-DNA and this data is also supported by molecular modeling (MD) studies.     

Fvp of bis- and tris-(pyrazol-1-yl)methane. A radical reaction

Flash vacuum pyrolysis of bis- and tris-(pyrazol-1-yl) methane was carried out. Alpha, gamma and radical eliminations were considered. The products actually formed correspond to a radical reaction. In the case of bis-(pyrazol-1-yl) methane, working at higher temperatures, pyrimidine was obtained. This compound is formed by rearrangement of a PzCH₂ radical.     

Spin transitions in a dithiazolyl radical: preparation, crystal structures, and magnetic properties of 3-cyanobenzo-1,3,2-dithiazolyl, C7H3S2N2

The incorporation of the electronegative cyano group into the structure of the title dithiazolyl radical 1 induces a lamellar packing motif that favors spin-transition behavior. Variable-temperature magnetic studies on 1 reveal a reversible phase transition at 250 K between a diamagnetic low-temperature phase and a paramagnetic high-temperature phase. X-ray crystal structures at 180(2) and 300(2) K reveal that both phases crystallize in the space group P2(1)/c, with the phase transition associated with a doubling of the crystallographic a axis. The concomitant change in magnetic properties is associated with a change from a paramagnetic regular pi stack of radicals and a diamagnetic distorted pi stack in which an energy gap opens up at the Fermi level corresponding to a Peierls-like transition.     

1,4-Hydrogen radical transfer as a new and versatile tool for the synthesis of enantiomerically pure 1,2,3-triols

[reaction: see text]1,4-Hydrogen radical transfers can now be reliably envisaged in radical synthetic chemistry as demonstrated by the formation of the cyano derivative II from I. Due to related sequences involving this new translocation process, followed by a highly diastereoselective trapping of the resulting anomeric radical, access to intriguing enantiopure 1,2,3-triols such as III is available.     

Density functional study of methyl radical association kinetics

Rate constants of the prototypical methyl-methyl radical association reaction are calculated on the basis of variational transition-state theory with a variable reaction coordinate and a multifaceted dividing surface. The potential energies required in the Monte Carlo integrations are evaluated directly using the M06 and M06-L density functionals. The rate constants are calculated at the canonical, microcanonical, and E,J-resolved microcanonical levels. The best prediction of rate constants is based on the potential energies calculated by the M06-L density functional; these agree with experimental data quantitatively from 300 to 1000 K. This study shows that density functional theory can be accurate enough for calculating rate constants of reactions with loose transition states, whereas previously only multireference wave function methods, which are more complicated and more expensive, had been demonstrated to be sufficiently accurate. The application of density functional theory for the loose transition states will allow larger and complicated systems to be studied efficiently.     

Molecular structures and supramolecular association of chlorodiorganotin(IV) complexes with bis- and tris-dithiocarbamate ligand

Two series of di and trinuclear chlorodiorganotin(IV) complexes derived from bis- and tris-dithiocarbamate ligands have been prepared and structurally characterized. The dinuclear complexes 1-2 of the composition {(R₂SnCl)₂(bis-dtc)} (1, R = Me; 2, R = ⁿBu) have been obtained from R₂SnCl₂ (R = Me, ⁿBu) and the triethylammonium salt of N,N′-dibenzyl-1,2-ethylene-bis(dithiocarbamate). The trinuclear complexes 3-9 with the general formula {(R₂SnCl)₃(tris-dtc)} 3, R = Me, tris-dtc = tris-dtc-Me; 4, R = Me, tris-dtc = tris-dtc-ⁱPr; 5, R = Me, tris-dtc = tris-dtc-Bn; 6, R = ⁿBu, tris-dtc = tris-dtc-Me; 7, R = ⁿBu, tris-dtc = tris-dtc- ⁱPr; 8, R = ⁿBu, tris-dtc = tris-dtc-Bn; 9, R = ^tBu, tris-dtc = tris-dtc-Me) were prepared from R₂SnCl₂ (R = Me, ⁿBu, ^tBu) and the potassium dithiocarbamate salts of (tris[2-(methylamino)ethyl]amine) (tris-dtc-Me), (tris[2-(isopropylamino)ethyl]amine) (=tris-dtc-ⁱPr) and (tris[2-(benzylamino)ethyl]amine) (=tris-dtc-Bn). Compounds 1-9 have been analyzed as far as possible by elemental analysis, FAB⁺ mass spectrometry, IR and NMR (¹H, ¹³C, ¹¹⁹Sn) spectroscopy, and single-crystal X-ray diffraction analysis. The solid state and solution studies showed that the dtc ligands are coordinated to the tin atoms in the anisobidentate manner. In all cases the metal centers are five-coordinate. The coordination geometry is intermediate between square-pyramidal and trigonal-bipyramidal coordination polyhedra with τ-values in the range of 0.32-0.53. For the members of each series characterized in the solid state by X-ray diffraction analysis, different molecular conformations were found. The crystal structures show the presence of C-H?Cl, C-H?S, C-H?π, S?Cl, S?S, Cl?Sn and S?Sn contacts.     

Predictive theory for hydrogen atom-hydrocarbon radical association kinetics

Procedures for accurately predicting the kinetics of hydrogen atom associations with hydrocarbon radicals are described and applied to a series of reactions. The approach is based on CASPT2/cc-pvdz evaluations of the orientation-dependent interaction energies within variable reaction coordinate transition state theory. One-dimensional corrections to the interaction energies are estimated from CAS+1+2/aug-cc-pvtz evaluations for the H + CH3 reaction, and a dynamical correction factor of 0.9 is applied. This corrected CASPT2 approach yields results that are within 10% of those obtained with the full CAS+1+2/aug-cc-pvtz potential for the H + CH3, H + C2H5, H + C2H3, and H + C2H reactions. New predictions are made for the H + iso-C3H7, H + tert-C4H9, H + C6H5, and H + C10H7 reactions. For the H + CH3 and H + C2H3 reactions, where the experimental values appear to be the most well-determined, theory and experiment essentially agree to within their error bars. For the other reactions, the agreement is reasonably satisfactory given the often large dispersion in the experimental results. For the reactions with saturated alkyl radicals, the theory predicts that each additional CH3 group increases the steric factor by approximately a factor of 2. In contrast, for the unsaturated radicals, the H + C6H5 and H + C10H7 high-pressure association rate coefficients are nearly identical to that for H + C2H3.     

Intramolecular dynamics of 1,2,3-trifluorobenzene radical anions as studied by OD ESR and quantum-chemical methods

Ab initio UMP2, RMP2, DFT/UB3LYP, and CBS-QB3 calculations have shown that the adiabatic potential energy surface (PES) of the 1,2,3-trifluorobenzene radical anion is a pseudorotation surface formed by nonplanar stationary structures. The low (approximately 2-4 kcal/mol) energy barriers in the path of pseudorotation imply manifestations of spectral exchange in the ESR spectra of this radical anion. The optically detected ESR of radical ion pairs was used to obtain the ESR spectrum of 1,2,3-trifluorobenzene radical anion in liquid squalane solution and to study temperature variations in the spectrum over the range of 243-325 K. The spectrum is a doublet of triplets with hfc constants of a(F(2)) = 29 mT and a(2F(1,3)) = 7.6 mT at T = 243 K. The experimental hfc constants are temperature-dependent. Calculations of the temperature dependence of hfc constants in the framework of the model of classical nuclei motion along the pseudorotation coordinate reproduce well the experimental data.     

Dimolybdenum bis-2,4,6-triisopropyl-benzoate bis-4-isonicotinate: a redox active analogue of 4,4'-bipyridine with ambivalent properties

The reaction between Mo2(TiPB)4 and 4-iso-nicotinic acid (2 equiv) in ethanol leads to the formation of trans-Mo2(TiPB)2(nic)2, I, where TiPB = 2,4,6-triisopropylbenzoate and nic = 4-isonicotinate. The molecular structures of I and I x 2DMSO were determined in the solid state by a single-crystal X-ray study, and its electronic structure was determined by DFT calculations on a model compound, where formate ligands were substituted for the bulky TiPB. The physicochemical properties of I are reported, and its potential as a redox active building block, a quasi-metalloorganic analogue of 4,4'-bipyridine, is described in the synthesis of molecular and solid-state assemblies. The molecular structure of I in the solid state consists of a 3-dimensional network in which each unit of Mo2(TiPB)2(nic)2 acts as a donor and acceptor via N to Mo coordination. In the structure of I x 2DMSO, the DMSO ligands coordinate axially with the Mo-Mo bond via oxygen. The reaction between I and Rh2(O2CMe)4 is shown to give a 1-D polymeric chain in the solid state: [{Rh2(O2CMe)4}{Mo2(TiPB)2(nic)2}] infinity, II. A similar structure was found for the product involving Rh2(O2CCMe3)4. Evidence is also reported for the formation of [(1,5-COD)MePt]2[mu-Mo2(TiPB)2(nic)2](PF6)2, III, and [(1,5-COD)Pt(mu-I)(PF6)2]n.     

Bimodal molecular weight distributions of a branched condensation polymer

Gel permeation chromatograms of a hindered-phenolic, branched condensation polymer display pronounced bimodality at high conversion. The true molecular weight distributions, obtained by means of a GPC calibration curve based on narrow-distribution fractions, exhibit corresponding anomalous high-molecular-weight “shoulders.” These results are discussed in terms of preferential aggregation and reaction of the higher-molecular-weight species during the polymerization, promoted by intermolecular hydrogen bonding in the apolar reaction medium.