The present report describes the first isolation of monomeric N-alkoxyarylaminyls and their chemical and magnetic properties. Reaction of the corresponding lithium amides of 2,4-diaryl-6-tert-butylanilines, 2,6-diaryl-4-tert-butylanilines, or 2,4,6-triarylanilines with tert-butyl peroxybenzoate in THF at -78 degrees C yielded quite persistent N-tert-butoxy-2,4-diaryl-6-tert-butylphenylaminyls (1), N-tert-butoxy-2,6-diaryl-4-tert-butylphenylaminyls (2), and N-tert-butoxy-2,4,6-triarylphenylaminyls (3), respectively, which were isolated in the monomeric form in 17-25% yields. All radicals prepared were oxygen insensitive and thermally very stable. X-ray crystallographic analyses were carried out for two radicals, and it was shown that the N and O atoms are coplanar with the anilino benzene ring. The ESR spectra of 1-3 gave a(N) = 0.984-1.05 and a(H) (anilino meta) = 0.158-0.170 mT (g = 2.0041-2.0043), indicating that the unpaired electron mainly resides on the nitrogen and anilino benzene ring. Magnetic susceptibility measurements for 1 and 3 showed that one radical revealed a weak ferromagnetic interaction and an analysis by the Curie-Weiss law gave 0.3 K as theta. The other radicals examined showed weak antiferromagnetic interactions and theta's were determined to be -0.3 to -1.5 K.
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.
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