Photochemical magnetism of crystalline 2,4,6-triazido-3,5-dichloropyridine

The magnetic properties and the buildup kinetics of the photolysis products of crystalline 2,4,6-triazido-3,5-dichloropyridine at temperatures of 2–300 K were studied with the use of a superconducting quantum interference device (SQUID). Under UV irradiation, the azide groups of the triazide decompose to afford high-spin nitrenes. The diamagnetic sample is converted into a paramagnetic with an average spin of 1.8 after 30 min of irradiation. The rate of triazide photolysis increases with a decrease in temperature down to 2 K.     

15N NMR spectra and reactivity of 2,4,6‐triazidopyridines, 2,4,6‐triazidopyrimidine and 2,4,6‐triazido‐s‐triazine

2,4,6‐Triazido‐s‐triazine, 2,4,6‐triazidopyrimidine and six different 2,4,6‐triazidopyridines were studied by ¹⁵N NMR spectroscopy. The assignment of signals in the spectra was performed using the gauge‐independent atomic orbital (GIAO)–Tao‐Perdew‐Staroverov‐Scuseria exchange‐correlation functional (TPSS)h/6‐311+G(d,p) calculations on the M06‐2X/6‐311+G(d,p) optimized molecular geometries. The Truhlar and coworkers' continuum solvation model called SMD was applied to treat solvent effects. With this approach, the root mean square error in estimations of the ¹⁵N chemical shifts for the azido groups was just 1.9 ppm. It was shown that the different reactivity of the α‐ and γ‐azido groups in pyridines correlates well with the chemical shifts of the N_α signals of these groups. Of two nonequivalent azido groups of azines, the azido group with the most shielded N_α signal is the most electron‐deficient and reactive toward electron‐rich reagents. By contrast, the azido group of azines with the most deshielded N_α signal is the most reactive toward electron‐poor reagents. Copyright © 2013 John Wiley & Sons, Ltd.     

The assignment of signals in the EPR spectra of axially symmetrical quintet dinitrenes

Fine structure levels in an external magnetic field and angular dependences of resonance magnetic fields on the direction of an external magnetic field were calculated for two axially symmetrical quintet dinitrenes with the zero-field splitting parameters D _q = 0.260 cm^?1, E _q = 0.000 and D _q = 0.243 cm^?1, E _q = 0.003 cm^?1. The EPR spectra of such dinitrenes contained lines of only three xy transitions (xy ₁, xy ₂, and xy ₄), two Δm _s = ±2 transition lines between the W _?2 and W ₀ sublevels, and three additional lines from noncanonically oriented molecules whose magnetic axis Z made an angle of 12°–16° or 52°–54° with an external magnetic field.     

Stereo- and regioselective cycloaddition of norbornene to 2,4,9-triazidopyridine

4-(3-Azatricyclo[3.2.1.0]oct-3-yl)-2,6-diazido-3,5-dicyanopyridine has been obtained by the reaction of 2,4,6-triazido-3,5-dicyanopyridine with an equimolar quantity of norbornene. The product reacted readily at room temperature with an excess of norbornene giving the corresponding trisazatricyclooctane cycloadduct. An analogous trisadduct was obtained in the reaction of 4-(3-azatricyclo[3.2.1.0]oct-3-yl)-1,6-diazido-3-chloro-5-cyanopyridine with norbornene on boiling in CCl₄, and also in ether at room temperature in the presence of the complexes Rh₂(OAc)₄ and Cu(AcAc)₂. The cycloaddition proceeds stereoselectively in all cases with the exclusive formation of exo-conformers. Calculations have been carried out using the PM3 and RHF/3-21G^* methods on 2,4,6-triazido-3-chloro-5-cyanopyridine and on 2,4,6-triazido-3,5-dicyanopyridine and also on the cycloadducts of these compounds with one or two molecules of norbornene. It was established that the addition of norbornene at the azide groups of pyridine is a dipole-LUMO controlled type of reaction and leads to the formation of cycloadducts having higher LUMO energy than the initial azides. The energy of the LUMO is increased to a lesser extent as a result of the addition of norbornene to a triazide containing identical substituents in the β positions of the pyridine ring, and is due to the special features of the symmetry of the LUMO of the cycloadducts formed. Institute of Chemical Physics in Chernogolovka, Russian Academy of Sciences, Chernogolovka 142432. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1521–1532, November, 1997.     

Regioselective and Regiospecific Cycloaddition of Acetylenes to 2,4,6-Triazidopyridine

The cycloaddition of tert-butylacetylene to 2,4,6-triazido-3,5-dicyanopyridine and 2,4,6-triazido-3-chloro-5-cyanopyridine occurs regioselectively and regiospecifically at the azide group in position 4 of the pyridine ring leading to the formation of the corresponding 4-(4'-tert-butyl-1H-1,2,3-triazolyl)pyridines as the sole products. Analogous reactions with the less sterically hindered n-butylacetylene are characterized by less regiospecificity and give a mixture of the isomeric 4'- and 5'-n-butyl-substituted triazoles at ratios of 96 : 4 and 91 : 9 respectively for the two different triazides. The interaction energies of the pyridine - and -azide groups with the acetylene molecules, and the energies of the transition states for these reactions have been calculated by the PM3 method. It was established that the high reactivity of the -azide group of the triazidopyridines in relation to the! ace tylenes is caused by the anomalously low distribution of bonding orbital density on these groups, leading to substantially lower activation energies in 1,3-dipolar cycloaddition reactions.     

Photochemical synthesis and properties of quintet pyridyl-2,6-dinitrenes

The structures and properties of quintet pyridyl-2,6-dinitrenes formed by low-temperature photolysis of 2,6-diazidopyridines were studied by ESR and quantum chemical (B3LYP/6-31G^*) methods. The synthesized dinitrenes represent a new type of quintet tetraradicals for which the ratio of zero-field splitting parameters is | E _q|/|D _q| = 1/3. This ratio is characteristic of quintet molecules in which the vector angle between two biradical centers is close to 114.5°. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1536–1540, September, 2006.     

Low-temperature photolysis of azidostyrylquinolines

Low-temperature photolysis of 2-and 4-(4′-azidostyryl)quinolines and azidohemicyanine dye, 1-methyl-4-(4′-azidostyryl)quinolinium iodide, was studied in an ether-ethanol matrix at 77 K and a methyltetrahydrofuran matrix at 5 K by means of electronic absorption spectroscopy and ESR technique. The formation of corresponding triplet nitrenes with absorption bands at 380–440 nm and zero-field splitting parameters of |D/h _cl = 0.781–0.790 cm^?1 and E = 0 was detected. It was found that the introduction of the positive charge into the azidostyrylquinoline molecule resulted in a bathochromic shift of the nitrene absorption band by ～40 nm and a decrease in the D by 0.005 cm^?1 due to charge transfer from the nitrene center to the quinoline moiety.     

Synthesis,structure, and characterization of high-energy 4,6-diazido-N-(4,6-diazido-1,3,5-triazin-2-yl)-1,3,5-triazin-2-amine

Chemistry of Heterocyclic Compounds - The high-energy compound 4,6-diazido-N-(4,6-diazido-1,3,5-triazin-2-yl)-1,3,5-triazin-2-amine was obtained in high yield by azidation of...