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

Abstract

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 Ag2O. An X-ray crystal and molecular structure analysis of the monoclinic single crystal with space group Cc showed that it has neither C3 symmetry nor zwitterionic quinonoid structure. An EPR spectrum in MTHF solution at room temperature consisted of seven lines (aN = 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-meth...