The Synthesis, Spectroscopic Observation and Chemical Reactivity of N-(2,2,6,6-Tetramethylpiperidyl)Ni trene

Author: Hinsberg, William Dinan, III

Year: 1980

Degree: Dissertation (Ph.D.)

Advisor: Dervan, Peter B.

Committee Member: Unknown, Unknown

Option: Chemistry

DOI: 10.7907/3R32-XC97

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) (λmax = 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 (kobs = 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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