Effect of spin density on the photochemical stability of aromatic nitrenes

Чапышев, С. В.

doi:10.1070/mc2003v013n02abeh001722

Cited by 23 publications

(8 citation statements)

References 19 publications

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“…Matrix photolysis of 2-azido-4,6-dichloroazido- s -triazine (eq ) yields the nitrene 306 , the tetraazacycloheptatetraene 307 , the diaazo compound 308 (type I ring opening), possibly the carbene 309 , and finally diisocyanodichloromethane. , …”

Section: Azidessupporting

confidence: 53%

Flash Vacuum Pyrolysis of Azides, Triazoles, and Tetrazoles

2017

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Flash vacuum pyrolysis (FVP) of azides is an extremely valuable method of generating nitrenes and studying their thermal rearrangements. The nitrenes can in many cases be isolated in low-temperature matrices and observed spectroscopically. NH and methyl, alkyl, aralkyl, vinyl, cyano, aryl and N-heteroaryl, acyl, carbamoyl, alkoxycarbonyl, imidoyl, boryl, silyl, phosphonyl, and sulfonyl nitrenes are included. FVP of triazoloazines generates diazomethylazines and azinylcarbenes, which often rearrange to the energetically more stable arylnitrenes. N elimination from monocyclic 1,2,3-triazoles can generate iminocarbenes, 1H-azirines, ketenimines, and cyclization products, and 1,2,4-triazoles are precursors of nitrile ylides. Benzotriazoles are preparatively useful precursors of cyanocyclopentadienes, carbazoles, and aza-analogues. FVP of 5-aryltetrazoles can result in double N elimination with formation of arylcarbenes or of heteroarylcarbenes, which again rearrange to arylnitrenes. Many 5-substituted and 2,5-disubstituted tetrazoles are excellent precursors of nitrile imines (propargylic, allenic, or carbenic), which are isolable at low temperatures in some cases (e.g., aryl- and silylnitrile imines) or rearrange to carbodiimides. 1,5-Disubstituted tetrazoles are precursors of imidoylnitrenes, which also rearrange to carbodiimides or add intramolecularly to aryl substituents to yield indazoles and related compounds. Where relevant for the mechanistic understanding, pyrolysis under flow conditions or in solution or the solid state will be mentioned. Results of photolysis reactions and computational chemistry complementing the FVP results will also be mentioned in several places.

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Section: Azidessupporting

confidence: 53%

Flash Vacuum Pyrolysis of Azides, Triazoles, and Tetrazoles

2017

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“…The UDFT calculations significantly overestimate the magnitude of D and underestimates the ratio E/D for trinitrene S-1. By contrast, the CASCI (12,12)/SVP calculations demonstrate excellent agreement with the experimental data. The analysis of the SS and SOC parts of the tensor D ̂shows that both methods predict essentially the same negative parameters D SS representing typical values for most of the septet trinitrenes.…”

Section: Methodsmentioning

confidence: 77%

“…High-spin nitrenes are highly reactive intermediates of the photolysis and thermolysis of aromatic polyazides, the spectral studies of which are possible only in cryogenic matrixes. These nitrenes have the largest zero-field splitting (ZFS) parameters D among all organic polyradicals and are of considerable interest as models for investigation of magnetism in molecular multispin systems. , Because the ZFS parameters of high-spin nitrenes strongly depend on spin densities on the nitrene units, the mutual orientation of these units, and the type of atoms in molecules, the studies of such nitrenes provide an unique opportunity to examine in detail the effect of subtle structural changes on magnetic characteristics of open-shell molecules. − The first electron spin resonance (ESR) spectra of quintet and septet nitrenes stabilized in frozen organic solutions were reported more than 40 years ago. , In the next 4 decades, dozens of various quintet dinitrenes and septet trinitrenes were investigated with X-band ESR spectroscopy in frozen organic solutions. , Unfortunately, many of the high-spin nitrenes appeared to be very reactive toward the organic solution molecules and could not be characterized with X-band ESR spectroscopy. − An important breakthrough in ESR studies of high-spin nitrenes took place only recently owing to the use of the matrix isolation of high-spin nitrenes in solid inert gases. Using this technique, such previously elusive septet trinitrenes as 1 – 4 , as well as many other high-spin nitrenes, were successfully stabilized in solid inert gases and characterized with X-band ESR spectroscopy (Scheme ). − Moreover, the use of the matrix-isolation technique made possible the registration of high-resolution X-band ESR spectra of high-spin nitrenes, which is of paramount importance in analysis of very complex spectra representing a superposition of ESR spectra of several high-spin species.…”

Section: Introductionmentioning

confidence: 99%

Heavy Atom Effect on Magnetic Anisotropy of Matrix-Isolated Monobromine Substituted Septet Trinitrene

et al. 2014

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The heavy atom effect on the magnetic anisotropy of septet trinitrenes is reported. Septet 1-bromo-3,5-dichloro-2,4,6-trinitrenobenzene (S-1) was generated in a solid argon matrix by ultraviolet irradiation of 1,3,5-triazido-2-bromo-4,6-dichlorobenzene. This trinitrene displays an electron spin resonance (ESR) spectrum that drastically differs from ESR spectra of all previously studied septet trinitrenes. The zero-field splitting (ZFS) parameters, derived from the experimental spectrum, show the parameter |D| = 0.1237 cm(-1) and the unprecedentedly large ratio of E/D = 0.262 that is close to the rhombic limit E/D = 1/3 for high-spin molecules. The CASCI (based on state-averaged CASSCF) and DFT methods were applied to calculate the ZFS tensor focusing on the heavy (bromine) atom effects on the spin-orbit term. These calculations show that the multiconfigurational ab initio formalism and the CASCI method are the most successful for accurate predictions of the spin-orbit term in the ZFS tensor of high-spin nitrenes containing heavy bromine atoms. Due to the presence of the bromine atom in S-1, the contribution of the spin-orbit term to the total parameter D is dominant and responsible for the unusual orientation of the easy Z-axis lying in the molecular plane perpendicular to the C-Br bond. As a result, the principal values D(XX), D(YY), and D(ZZ) of the total tensor D̂(Tot) have such magnitudes and signs for which the ratio E/D is close to the rhombic limit, and the total parameter D is large in magnitude and positive in sign.

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“…Furthermore, Chapyshev has investigated the matrix photolysis of azido- s -triazine 29 and suggested the ring-opening of tetraazacycloheptatetraene 31 (1951 cm –1 ) to the isocyano diazo compound 32 (2087 cm –1 ) (eq ) …”

Section: Resultsmentioning

confidence: 99%