Tris[p-(N-oxyl-N-tert-butylamino)phenyl]amine, -methyl, and -borane Have Doublet, Triplet, and Doublet Ground States, Respectively

N, N, N -Tris[ p -( N -oxyl- tert -butylamino)phenyl]amine ( N ) was obtained as dark violet plates by lithiation of tris(4-bromophenyl)amine, followed by reaction with 2-methyl-2-nitrosopropane and oxidation of the resulting tris(hydroxyamine) with Ag 2 O. An X-ray crystal and molecular structure analysis of the monoclinic single crystal with space group Cc showed that it has neither C 3 symmetry nor zwitterionic quinonoid structure. An EPR spectrum in MTHF solution at room temperature consisted of seven lines ( a N = 4.06 G (3N) at g = 2.0058). The temperature dependence of the magnetic susceptibility data on N in the range 2−300 K was analyzed in terms of a triangular coupling model for three S = 1/2 spins to give a set of best-fit parameters which placed a doublet state as the ground state with a quartet state lying 559 K (= 1.11 kcal mol - 1 ) above it. B3LYP/6-31G*//B3LYP/6-31G computations were performed on both spin states of a model molecule ( N ‘) in which all three N - tert -butyl groups in N were replaced with N -methyl groups. The doublet state was found to be more stable than the quartet state by 0.84 kcal mol - 1 . Tris[ p -( N -oxyl- tert -butylamino)phenyl]methyl ( C ) gave a monoclinic single crystal with space group Cc (no. 9) and has been shown to have a benzoquinoneimine N -oxide type diradical structure. Temperature dependence of its magnetic susceptibility showed that C has a triplet ground state with a singlet state lying 410 K above the triplet. Reactions of the corresponding organolithium compounds with BF 3 ·OEt 2 were not applicable to give tris[4-( N -oxyl- tert -butylamino)phenyl]borane ( B ) but its 2,2‘,2‘ ‘,6,6‘,6‘ ‘-hexamethyl derivative ( B ‘). In the trigonal crystal with space group R 3̄ (no. 148), the three benzene rings are tilted by 49.2° with respect to the valence plane of the boron atom. The magnetic susceptibility data on B ‘ were consistent with a doublet ground state with an energy gap to a quartet state by 9.9 K (= 0.0197 kcal mol - 1 ). All the results together with ab initio MO studies are consistent with a picture that the ground spin states of title compounds N, C, and B are doublet, triplet, and doublet, respectively. The electronic structures are explained qualitatively by p -( N -oxyl- tert -butylamino)phenyl homologues of (•H 2 C) 3 X in which X = N, C·, and B atoms, and two, one, and no π-electrons are contained, respectively.