Synthesis and structural analysis of bis(2-hydroxyphenyl) phenylamine, PhN(o-C6H4OH)2:: Comparison with tris(2-hydroxyphenyl)amine N(o-C6H4OH)3

The molecular structures of N(o-C6H4OH)(3), PhN(o-C6H4OH)(2), andp-TolN(o-C6H4OMe)(2) have been determined by X-ray diffraction, thereby indicating several structural differences. For example, whereas the nitrogen in N(o-C6H4OH)(3) is pyramidal with Sigma(C-N-C) = 348.3 degrees, the nitrogen atoms in PhN(o-C6H4OH)(2) andp-TolN(o-C6H4OMe)(2) are trigonal planar with Sigma(C-N-C) = 359.9 degrees and Sigma(C-N-C) = 360.0 degrees, respectively. The phenyl andp-tolyl groups of PhN(o-C6H4OH)(2) andp-TolN(o-C6H4OMe)(2) lie close to the trigonal plane, while theo-C6H4OH ando-C6H4OMe groups are almost orthogonal to this plane. The coplanar and orthogonal orientations of the aryl groups of PhN(o-C6H4OH)(2) andp-TolN(o-C6H4OMe)(2) are in marked contrast to those of the phenyl groups within Ph3N, which exhibit dihedral angles in the range 38-52 degrees and approximateD(3) symmetry. The observed structures of PhN(o-C6H4OH)(2) andp-TolN(o-C6H4OMe)(2) may be rationalized in terms of maximizing delocalization of the nitrogen lone pair into the phenyl andp-tolyl groups, while minimizing unfavorable overlap with theo-C6H4OH ando-C6H4OMe groups due to the presence of pi-donatingortho-substituents; the orthogonal orientation of theo-C6H4OH ando-C6H4OMe groups is also one that minimizes unfavorable steric interactions between theortho-substituents.