Time-Resolved Resonance Raman Study of Triplet Arylnitrenes and Their Dimerization Reaction

Abstract

Time-resolved resonance Raman spectra for triplet 4-methoxyphenyl nitrene and 4-ethoxyphenyl nitrene and their dimerization reaction to form azo dimer products in acetonitrile solution on the nanosecond time scale are reported. As the 4-methoxyphenyl nitrene and 4-ethoxyphenyl nitrene Raman bands decay, the Raman bands for the azo dimer products increase in intensity. The triplet 4-methoxyphenyl nitrene and 4-ethoxyphenyl nitrene species and their reaction to produce azo products are compared to a recent study of the 2-fluorenyl nitrene species and its reaction to form dehydroazepine ring-expansion products. The properties of the singlet and triplet arylnitrenes and their reaction mechanisms to form azo dimer and ring-expansion products are briefly discussed.

Time‐resolved resonance Raman and density functional theory investigation of the 4‐biphenylnitrene dimerization reaction

“…All the data for 4-methoxyphenylnitrene and its azo dimer product presented here are based on our previous results. 56 The C-N bond of triplet 4-methoxyphenylnitrene is 1.3296Å. The C-N bond of triplet 4-methoxyphenylnitrene is longer than that of triplet 4-biphenylnitrene.…”

“…The N N bond of the azo dimer product with the 4-methoxyphenyl (1.2791Å) substituent 56 is longer than that for the 4-biphenyl (1.2778Å) substituent (see Fig. 2).…”

“…From a previous study, it was found that the singlet 4methoxyphenyl-and 4-ethoxyphenylnitrenes undergo a very fast ISC process to give triplet nitrenes. 56 Hence it is of interest to compare them with the 4-biphenylnitrenes studied here. Since the 4-methoxyphenyl-and 4-ethoxyphenylnitrenes have similar imino/cyclohexadienyl characters (in which the 4-methoxyphenylnitrene has a slightly larger imino/cyclohexadienyl character than the 4-ethoxyphenylnitrene), 4methoxyphenylnitrene will be used as a representative 4alkoxyphenylnitrene for comparison with 4-biphenylnitrene.…”

“…In our previous study on alkoxyphenyl nitrenes, the TR 3 spectra for triplet 4alkoxyphenylnitrenes and their azo dimer products were observed. 56 Hence it is of interest to compare their structures and properties in order to understand better p-phenyl substitution effects on arylnitrenes and azo dimer products.…”

A Laser Flash Photolysis Study of Azo-Compound Formation from Aryl Nitrenes at Room Temperature

“…Phenyl nitrene, with an E ST of 14.6 kcal/mol (B3LYP/6-311+G(2df,p) level of theory), lies between these species, but its room temperature chemistry is dominated by that of the singlet nitrene. Para-substitution with strongly electron donating groups provides access to triplet species with similar E ST , 12 and a resonance Raman study by Phillips et al 40 suggests that p-methoxy-and p-ethoxyphenyl azide yield their respective azo-dimers following laser photolysis, although the kinetics of formation were not unambiguously established.…”