Nitrenes matrix photochemistry

Morawietz, J. Sander, W. Photochemistry of fluorinated phenyl nitrenes matrix isolation of fluorinated azirines, J. Org. Chem. 1996, 61,4351-4354. 

Platz, M.S., Leyva. E., Haider, K. (1991), Selected Topics in the Matrix Photochemistry of Nitrenes, Carbenes, and Excited Triplet States, Org. Photochem. (Padwa, A., Ed.) 11, 367. 

As discussed by Bally [33], matrix photochemistry has obtained excellent results, provided that back reaction is not overwhelming. This is a problem with radicals, much less for carbenes and nitrenes when formed by elimination reactions from diazo compounds and respectively azides. In the latter case, N2 is eliminated with no significant alteration of the matrix. There are exceptions, however, as is the case of parent carbene, the identification of which has long been hindered by the efficient recombination occurring, and finally demonstrated by exchange [42]. 

The matrix photochemistry of phenyl nitrenes becomes more complex when substituents are present that can take an active part in the reactions. For instance, irradiation of azide 79 in Ar matrices gave a product (80) from nitrene insertion into an adjacent CH bond as well as the ring-expanded ketenimine 81. The nitrene center can also react by attack on oxygen. Thus, the photolysis of 2-(methoxycarbo-nyljphenyl azide (82) in Ar matrices gave rise to at least five major products nitrene 83, cycKc ketenimine 84, the two geometrical isomers of ketene-oxime 86, and N-methoxyazetinone 87 (Scheme 10). Products... 

Fig. 5. Chemistry of cyclized mbbei—bis-a2ide negative acting resist, (a) Preparation of cyclized mbber resin from polyisoprene (b) photochemistry of aromatic bis-a2ide sensiti2ers. The primary photoproduct is a highly reactive nitrene which may combine with molecular oxygen to form oxygenated products, or may react with the resin matrix by addition or insertion to form polymer—polymer linkages.

Reiser followed the photochemistry of this azide in organic glasses at 77 K [20], After brief photolysis the UV-VIS spectrum of the triplet nitrene was observed. Upon warming and recooling the matrix, the spectrum of the triplet nitrene disappeared and was replaced by that of carbazole. 

The formation of highly strained bridgehead imines was observed on the irradiation of a series of matrix-isolated bridgehead azides.The photochemistry of matrix-isolated 1-azidonorbornane (6) was studied using monochromatic irradiation IR, UV, and ESR spectroscopy and trapping with methanol and CO. The azide photochemistry was very complicated, and the formation of two types of imines (7 and 8) and triplet nitrene 9 were observed. 

In order to determine experimentally the multiplicity and the structure of the lowest state of benzoylnitrene (25), a study of the photochemistry of benzoyl azide (24) was performed in an Ar matrix at 12 K. The formation of two species was observed upon exposure of 24 to 254 nm light. One of these species has an IR spectrum, which is consistent with that expected for phenyl isocyanate (45). The IR and UV spectrum of the second intermediate are in very good agreement with the calculated spectra of singlet nitrene in the A state (25). This intermediate undergoes isomerization to isocyanate (45) upon further exposure of the sample to 313-nm light. 

Tetrazoles tautomeric with azides and their (selective) photochemistry in matrix are a favorite topic of mechanistic investigation (see the chapter by Fausto in Vol. 39 of this series)." Recent reports concern tetrazolyl-1,2.4-triazoles, and a tetrazolylethanol." On the other hand, preliminary data about the photochemistry of the 2-azido analogue of 2 -deoxyuridine (that exists as the tetrazole tautomer) have been reported, showing the formation of the corresponding amine." Non nitrene paths can also be followed, as in the case of some phenyltetrazolethione that cleave forming an open-chain diradical that in turn loses a sulfur atom (Scheme 15). ... 

The photochemistry of HN3 in the argon and nitrogen matrices was studied for the first time by J. Pimentel et al. and the IR spectra of triplet nitrene NH and radical NH2 were recorded. A series of studies of matrix isolated NH (in ground triplet and excited singlet A states) and its deutero-substitute analogue (ND) were later performed using UV and luminescence spectroscopy. " The spectroscopy and relaxation of the lowest excited singlet state of NH / ND ( A) were studied in detail in Ne, Ar, Kr and Xe matrices... 

Since there is no evidence of nitrene intermediates in the solution photochemistry of alkyl azides, attempts were made to detect triplet alkylnitrenes in matrix photochemical experiments. Photolysis of CH3N3 or CD3N3 at cryogenic temperatures in Ar, N2 and CO2 matrices fails to produce an IR spectrum attributable to triplet methylnitrene. The IR spectrum of imine CH2=NH (or CD2=ND) is observed instead. 

Tomioka, H., Ichikawa, N., and Komatsu, K., Photochemistry of 2-(methoxycarbonyl)phenyl azide studied by matrix-isolation spectroscopy. A new sHppery energy surface for phenyl nitrene, /. Am. Chem. Soc., 115, 8621,1993. 

The photochemistry of azidotriazines depends on substitution. Photolysis of 2-azido-4,6-dichloro-1,3,5-triazine 108, matrix-isolated in Ar at 10 K, led to formation of both triplet nitrene 109 and didehydrotetrazepine 110, which could be interconverted photochemically. Extended photolysis, however, resulted in the formation of an unidentified ring-opened product." Laser flash photol) is experiments indicate that both 109 and 110 are formed at ambient temperature." ... 

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