Synthesis, Spectroscopy, X-ray Structure and Redox Behaviors of 4-(N-R-salicylideneimine)-2,6-diphenylphenols

Abstract

A series of sterically hindered 4- (N-R-salicylaidimine)-2,6-diphenylphenols (X), where R = H (1), 3-CH3 (2), 5-CH3 (3), 3-OCH3 (4), 4-OCH3 (5), 5-OCH3 (6), 3-Bu-t (7), 5-Bu-t (8), 3,5-Bu-t(2)(9) and 5,6-benzo(10), were synthesized and their structure as well as redox behavior studied by analytical, spectroscopic [H-1, (C-13) NMR, IR, UV-vis and mass spectrometry] and cyclic voltammetric (CV) techniques. Single crystal X-ray diffraction studies of 7 evidenced its existence as non-planar enol-imine tautomer structure, in which the phenol ring of the molecule is twisted around C-N single bond by 21.5(2)degrees. The packing structure of 7 is stabilized by C-H center dot center dot center dot pi(Ph) and O center dot center dot center dot O and C center dot center dot center dot O intermolecular short contact interactions. The CV of X display rate is dependent on irreversible and quasi-reversible redox waves in the anodic and cathodic regions due to oxidation and reduction of phenolic and iminic groups, respectively. As evidenced by ESR and UV-vis study, chemical oxidation of X by PbO2 and (NH4)(2)Ce(NO3)(6) in MeCN and CHCl3 generates stable phenoxyl radicals [(g similar to 2.005 and lambda similar to 450 nm (1600-8200 M-1 cm(-1))]. (C) 2007 Elsevier B.V. All rights reserved.