N-tert-Butoxy-1-aminopyrenyl Radicals. Isolation, Electronic Structure, and Magnetic Characterization¹

Abstract

N-tert-Butoxy-2,7-di-tert-butyl-1-pyrenylaminyl (4), N-tert-butoxy-2-tert-butyl-1-pyrenylaminyl (5), and N-tert-butoxy-7-tert-butyl-1-pyrenylaminyl (6) free radicals were generated by the reaction of the lithium amides of the corresponding 1-aminopyrenes with tert-butyl peroxybenzoate in THF at -78 degrees C. Although 6 could not be isolated due to the gradual decomposition in solution, 4 and 5 were quite persistent and could be isolated as monomeric radical crystals. The X-ray crystallographic analyses for the isolated free radicals were successfully carried out, indicating that the N and O atoms are almost coplanar with the pyrene ring. The ESR spectra of 4 and 5 were very complex due to the presence of many magnetically unequivalent protons. Therefore, the proton hyperfine coupling (hfc) constants were determined by (1)H ENDOR/TRIPLE resonance spectroscopy. To assign the hfc constants for the pyrene ring protons, a partially deuterated radical, 4-d(4), was prepared and the ENDOR and ESR spectra were measured. To discuss the spin density distribution for 4 and 5 ab initio molecular orbital calculations were performed by the DFT UBecke 3LYP method, using the STO 6-31G basis set. Magnetic susceptibility measurements were carried out for 4 and 5 with a SQUID magnetometer. For 4 a weak antiferromagnetic interaction was observed, and for 5 a very strong antiferromagnetic interaction was observed. The antiferromagnetic interactions were explained by their crystal structures.

Tetramethoxypyrene-Based Biradical Donors with Tunable Physical and Magnetic Properties

“…To the best of our knowledge, only C1-substituted pyrene-based (Scheme ) neutral monoradicals are known; nonetheless, no pyrene-based biradical has been reported to date. Pyrene is a unique example of polyaromatic hydrocarbons with a nodal plane passing through the 2,7 positions .…”

Electrochemical study of stable N-alkoxyarylaminyl radicals

“…Although N-alkoxyaminyl radicals were extensively studied by ESR spectroscopy over a long time [1][2][3][4][5][6][7][8][9][10], the first isolation of N-alkoxyaminyls by our group was quite recent [11][12][13][14][15][16][17]. We obtained isolable N-alkoxyarylaminyls by two methods.…”

“…We obtained isolable N-alkoxyarylaminyls by two methods. One method involves the reaction of the lithium salts of 2,4,6-tri-substituted anilines with tert-alkyl peroxybenzoates [11][12][13][14][15] and the other involves the reaction of 2,4-diaryl-6-tert-butylnitrosobenzenes with azo compounds [16,17]. Interestingly, the isolated N-alkoxyarylaminyls are stable in the presence of oxygen even in solution and, although they were heated at 80 • C in benzene for 10 days, 80% of the radical survived.…”

Isolation and Magnetic Properties of Heterocycle-Carrying N-Alkoxyarylaminyl Radicals1

“…However, quite recently, the first isolation of N -alkoxylaminyls was accomplished by our group. The isolated N -alkoxyaminyls are N - tert -butoxy-2,4,6-triaryl-, N - tert -butoxy-2- tert -butyl-4,6-diaryl-, and N - tert -butoxy-4- tert -butyl-2,6-diarylphenylaminyls and N - tert -butoxy-2- tert- butyl- and N - tert -butoxy-2,6-di- tert -butyl-1-pyrenylaminyls, which are sterically protedted . Interestingly, the isolated N -alkoxyaminyls were shown to be oxygen-insensitive, even in solution.…”

“…Radicals 1 and 2 were prepared by the reaction of the lithium salts ( 6 and 10 ) of 2,6-diaryl-4-(4-pyridyl)phenylanilines ( 5 ) or 2,6-diaryl-4-(1 H -imidazol-1-yl)phenylanilines ( 9 ) with tert -butyl peroxybenzoate in THF at −78 °C. ,, The preparation of 5 and 9 is shown in Schemes and . When a THF solution of tert -butyl peroxybenzoate was added to a solution of 6 or 10 in THF, the resultant mixtures immediately showed a characteristic red color.…”