2,4,6-Triazido-1,3,5-Triazine, 2,4,6-Triazidopyrimidine,and 2,4,6-Triazidopyridine as Precursors of Carbon Nitride Materials

The thermolysis of 2,4,6-triazido-1,3,5-triazine (I), 2,4,6-triazidopyrimidine (II), and 2,4,6-triazidopyridine (III) and its products were studied by DSC, mass spectrometry, IR spectroscopy, and electron microscopy. The thermal transformations of I gave planar nets formed by polyconjugated C–N bonds arranged into bundle aggregates. The thermolysis product of III consists of low-molecular compounds and has globular morphology. The thermolysis of II resulted in a mixture of products of both types, among which the planar nets were dominant. The relationship between the structure of the products of the thermal transformations of I, II, and III and the kinetic characteristics of these processes was discussed.     

EPR Studies on Branched High‐Spin Arylnitrenes

The UV (λ>305 nm) photolysis of triazide 3 in 2‐methyl‐tetrahydrofuran glass at 7 K selectively produces triplet mononitrene 4 (g=2.003, D_T=0.92 cm^?1, E_T=0 cm^?1), quintet dinitrene 6 (g=2.003, D_Q=0.204 cm^?1, E_Q=0.035 cm^?1), and septet trinitrene 8 (g=2.003, D_S=?0.0904 cm^?1, E_S=?0.0102 cm^?1). After 45 min of irradiation, the major products are dinitrene 6 and trinitrene 8 in a ratio of ～1:2, respectively. These nitrenes are formed as mixtures of rotational isomers each of which has slightly different magnetic parameters D and E. The best agreement between the line‐shape spectral simulations and the experimental electron paramagnetic resonance (EPR) spectrum is obtained with the line‐broadening parameters Γ(E_Q)=180 MHz for dinitrene 6 and Γ(E_S)=330 MHz for trinitrene 8 . According to these line‐broadening parameters, the variations of the angles Θ in rotational isomers of 6 and 8 are expected to be about ±1 and ±3°, respectively. Theoretical estimations of the magnetic parameters obtained from PBE/DZ(COSMO)//UB3LYP/6‐311+G(d,p) calculations overestimate the E and D values by 1 and 8 %, respectively. Despite the large distances between the nitrene units and the extended π systems, the zero field splitting (zfs) parameters D are found to be close to those in quintet dinitrenes and septet trinitrenes, where the nitrene centers are attached to the same aryl ring. The large D values of branched septet nitrenes are due to strong negative one‐center spin–spin interactions in combination with weak positive two‐center spin–spin interactions, as predicted by theoretical considerations.     

The Lifetime and Reactivity of Singlet Tetrachloropyridyl-4-nitrene

The principal direction in the photolytic decomposition of 4-azidotetrachloropyridine in methylene chloride solution involves the intermediate formation of singlet tetrachloropyridyl-4-nitrene, the lifetime of which amounts to 50 nsec. The nitrene reacts readily with the pyridine (k _pyr = 2.67·10⁷ mole^-1·sec^-1) with the formation of the corresponding pyridinium ylide, which has a characteristic absorption band in the UV spectrum with a maximum at 406 nm.     

Quantum chemical study of the nature of regioselectivity in reactions of 2,4,6-triazidopyridines withtert-butylphosphaacetylene

We have performed PM3 calculations for 2,4,6-triazido-3,5-dicyanopyridine and 2,4,6-triazido-3-chloro-5-cyanopyridine, and also the cycloadducts of these compounds with one and two tert-butylphosphaacetylene molecules. We have established that the selectivity of addition of a phosphaacetylene molecule at the -azido group of triazidopyridines is due to the specifics of the electronic properties and geometry of these groups, characterized by enhanced electrophilicity of the terminal nitrogen atoms, a greater contribution from atomic orbitals to the LUMO (lowest unoccupied molecular orbital), and greater bending of the chain of N–N–N atoms. The cycloaddition itself corresponds to the dipole-LUMO-controlled reaction type, and sequential addition of phosphaacetylene molecules at the azido groups of pyridines leads to formation of cycloadducts having lower LUMO energies. Nevertheless, the -azido groups of the triazidopyridines can remain stronger dipoles than the azide groups of the cycloadducts when the difference between the LUMO energies in the triazidopyridines and cycloadducts is no greater than 10 kcal/mole.Institute of Chemical Physics at Chernogolovka, Russian Academy of Sciences, Chernogolovka 142432. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 676–686, May, 1997.     

Selective Thermolysis of Azide Groups in 2,4,6-Triazidopyridines

When refluxed in 1,4-dichlorobenzene, the compound 2,4,6-triazido-3,5-dichloropyridine and its 3,5-dicyano derivative undergo selective thermolysis of the -azide groups, forming the corresponding 4-amino-2,6-diazidopyridines in high yields. According to quantum-chemical calculations, the selectivity of thermolysis of the -azide groups in triazides is due to the weaker bonding interactions between the N₍₎ and N₍₎ atoms in these azide groups.     

Synthesis of 2-pyridyl-substituted derivatives of 7-benzyl-5,6,7,8-tetra-hydropyrido[3,4-<Emphasis Type="Italic">d</Emphasis>]pyrimidine

A method has been developed for the synthesis of 2-pyridyl-substituted derivatives of 7-benzyl-5,6,7,8-tetrahydropyrido[3,4-d]pyrimidine based on the condensation of ethyl 1-benzyl-3-oxopiperidine-4-carboxylate with pyridyl-2-, pyridyl-3-, and pyridyl-4-carboxamidines and subsequent reactions of 7-benzyl-2-pyridyl-5,6,7,8-tetrahydro-3H-pyrido[3,4-d]pyrimidin-4-ones with trifluoromethanesulfonic anhydride and secondary amines. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, 1556–1561, October, 2007.     

Cine-substitution in reactions of dichloro-1,4-benzoquinones with pyrrolidine

Products ofcine-substitution are formed in reactions of 2,5- and 2,6-dichloro-1,4-benzoquinones with pyrrolidine. The main reason for amination of chloroquinones by pyrrolidinevia the mechanism ofcine-substitution is the high basicity of this amine. A high degree of localization of the -bond in the molecules of the starting chloroquinones and the strong conjugation of the amino group with the quinone ring in the molecules of the intermediate monoaminoquinones are two other factors that favor an increase in yields of the products ofcine-substitution.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2702–2709, November, 1996.     

Photochemical synthesis and ESR spectra of quintet meta-phenylenedinitrenes

Relationships between the molecular structures and zero-field splitting parameters of quintet m-phenylenedinitrenes formed during the photolysis of 1,3-diazidobenzenes in 2-methyltetrahydrofuran solutions frozen at 77 K were studied by ESR spectroscopy and B3LYP/6-31G* calculations. Simulations of the W₋₂/W₋₁, W₊₂/W₊₁, W₋₁/W₀, W₊₁/W₀, and W₊₂/W₀ (Δm _s = 2) transitions were performed for the first time and all signals in the ESR spectra of quintet m-phenylenedinitrenes were unambiguously assigned. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1085–1089, July, 2006.     

13C and 15N NMR spectra of high‐energy polyazidocyanopyridines

¹³C and ¹⁵N NMR spectra of high‐energy 2,4,6‐triazidopyridine‐3,5‐dicarbonitrile, 2,3,5,6‐tetraazidopyridine‐4‐carbonitrile and 3,4,5,6‐tetraazidopyridine‐2‐carbonitrile are reported. The assignment of signals in the spectra was performed on the basis of density functional theory calculations. The molecular geometries were optimized using the M06‐2X functional with the 6‐311+G(d,p) basis set. The magnetic shielding tensors were calculated by the gauge‐independent atomic orbital method with the Tao–Perdew–Staroverov–Scuseria hybrid functional known as TPSSh. In all the calculations, a polarizable continuum model was used to simulate solvent effects. This approach provided accurate predictions of the ¹³C and ¹⁵N chemical shifts for all the three compounds despite complications arising due to non‐coplanar arrangement of the azido groups in the molecules. It was found that the ¹⁵N chemical shifts of the N_α atoms in the azido groups of 2,4,6‐triazidopyridines correlate with the ¹³C chemical shifts of the carbon atoms attached to these azido groups. Copyright © 2016 John Wiley & Sons, Ltd.     

EPR spectroscopy of multicomponent,multispin molecular system obtained by the photolysis of 2,4,6-triazido-3-cyano-5-fluoropyridine in solid argon

Complex multicomponent, multispin molecular system, consisting of a septet trinitrene, two quintet dinitrenes, and three triplet mononitrenes, was obtained by the photolysis of 2,4,6-triazido-3-cyano-5-fluoropyridine in solid argon. To identify these paramagnetic products, electron paramagnetic resonance spectroscopy in combination with line-shape spectral simulations and density functional theory calculations was used. The products of the photolysis was found to be triplet 2,4-diazido-3-cyano-5-fluoropyridyl-6-nitrene (D_T = 1.000 cm⁻¹, E_T = 0), triplet 2,4-diazido-3-cyano-5-fluoropyridyl-2-nitrene (D_T = 1.043 cm⁻¹, E_T = 0), triplet 2,6-diazido-3-cyano-5-fluoropyridyl-4-nitrene (D_T = 1.128 cm⁻¹, E_T = 0 cm⁻¹), quintet 4-azido-3-cyano-5-fluoropyridyl-2,6-dinitrene (D_Q = 0.211 cm⁻¹, E_Q = 0.0532 cm⁻¹), quintet 2-azido-3-cyano-5-fluoropyridyl-4,6-dinitrene (D_Q = 0.208 cm⁻¹, E_Q = 0.0386 cm⁻¹), and septet 3-cyano-5-fluoropyridyl-2,4,6-trinitrene (D_S = −0.1017 cm⁻¹, E_S = −0.0042 cm⁻¹) in a 38:4:7:22:14:4 ratio, respectively.