The synthesis, spectroscopic observation and chemical reactivity of N-(2,2,6,6-tetramethylpiperidyl)nitrene

Citation

Hinsberg, William Dinan, III (1980) The synthesis, spectroscopic observation and chemical reactivity of N-(2,2,6,6-tetramethylpiperidyl)nitrene. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/3R32-XC97. https://resolver.caltech.edu/CaltechTHESIS:07252016-112114482

Abstract

1,1-Dialkyldiazenes (aminonitrenes, N-nitrenes) unlike their more stable 1,2-dialkyldiazetle isomers (azo compounds) have not yet been isolated or detected by spectroscopic methods, but rather are assumed intermediates based on a substantial body of chemical evidence. The first direct observation of a 1,1- dialkyldiazene is described here. The visible spectrum at -78° of N-(2,2,6,6-tetramethylpiperidyl)nitrene (33) (λ_max = 541 nm) provides experimental evidence on (1) the energy required for the n + π* electronic transition, and (2) the vibrational spacing of the first electronically excited state. The infrared spectrum at -78° (¹⁴N=¹⁴N stretch at 1595 cm^-1; ¹⁴N=¹⁵N stretch at 1569 cm^-1) provides evidence that the 1,1- diazene has considerable N=N double bond character in the ground state.

The first kinetic study of the thermal decomposition of a 1,1-dialkyldiazene is described. The temperature dependence of the unimolecular rate (k₁) of fragmentation of 33 was examined in three different solvents and kinetic evidence for a direct bimolecular pathway for the formation of 1,1 "-azo-2,2,6,6-tetra- methylpiperidine 41 from 33 is provided. The activation parameters for the unimolecular fragmentations are log A = 11.6 ± 0.5, Ea = 16.9 ± 0.7 in n-hexane, log A = 13.7 ± 0.3, Ea = 20.0 ± 0.4 in Et₂0, log A= 13.6 ± 0.3, Ea = 20.1 ± 0.4 kcal/mole in THF. Using computer simulation it is found that the curved portions of the tn A vs. time plots may be modelled as competitive unimolecular and bimolecular reactions (k_obs = k₁ + k₂[33]). In Et₂0 at -16°, k₁ = 5.03 x 10^-4 sec^-1 and k₂ = 5.0 x 10^-2 liter/mole-sec.

Also reported are proton and carbon-13 nuclear magnetic resonance data for 33, along with the results of a preliminary study of its photoreactivity.

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