Synthesis and Characterization of 1,1-Di-Tert-Butyldiazene

Citation

McIntyre, Daniel Keith (1983) Synthesis and Characterization of 1,1-Di-Tert-Butyldiazene. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/y54d-s069. https://resolver.caltech.edu/CaltechTHESIS:12022013-142422017

Abstract

The synthesis and direct observation of 1,1-di-tert-butyldiazene (16) at -127°C is described. The absorption spectrum of a red solution of 1,1-diazene 16 reveals a structured absorption band with λ_max at 506 nm (Me₂O, -125°C). The vibrational spacing in S₁ is about 1200 cm^-1. The excited state of 16 emits weakly with a single maximum at 715 nm observed in the fluorescence spectrum (Me₂O:CD₂Cl₂, -196°C). The proton NMR spectrum of 16 occurs as a singlet at 1.41 ppm. Monitoring this NMR absorption at -94⁰ ± 2°C shows that 1,1-diazene 16 decomposes with a first-order rate of 1.8 x 10^-3 sec^-1 to form isobutane, isobutylene and hexarnethylethane. This rate is 10⁸ and 10³⁴ times faster than the thermal decomposition of the corresponding cis and trans 1,2-di-tert-butyldiazene isomers. The free energy of activation for decomposition of 1,1-diazene 16 is found to be 12.5 ± 0.2 kcal/mol at -94°C which is much lower than the values of 19.1 and 19.4 kcal/lmole calculated at -94°C for N-(2,2,6,6-tetramethylpiperidyl)nitrene (3) and N-(2,2,5,5-tetramethylpyrrolidyl)nitrene (4), respectively. This difference between 16 and the cyclic-1,1-diazenes 3 and 4 can be attributed to a large steric interaction between the tert-butyl groups in 1,1-diazene 16.

In order to investigate the nature of the singlet-triplet gap in 1,1-diazenes, 2,5-di-tert-butyl-N-pyrrolynitrene (22) was generated but was found to be too reactive towards dimerization to be persistent. In the presence of dimethylsulfoxide, however, N-pyrrolynitrene (22) can be trapped as N-(2,5-di-tert-butyl-N'-pyrrolyl)dimethylsulfoximine (38). N-(2,5-di-tert-butyl-N'-pyrrolyl)-d⁶-dimethylsulfoximine (38-d⁶) exchanges with free dimethylsulfoxide at 50°C in solution, presumably by generation and retrapping of pyrrolynitrene 22.

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