Synthesis, spectroscopy, X-ray structure and redox behaviors of 4-( N- R-salicylideneimine)-2,6-diphenylphenols

A series of sterically hindered 4-( N- R-salicylaldimine)-2,6-diphenylphenols ( X), where R = H ( 1), 3-CH 3 ( 2), 5-CH 3 ( 3), 3-OCH 3 ( 4), 4-OCH 3 ( 5), 5-OCH 3 ( 6), 3- t Bu ( 7), 5- t Bu ( 8), 3,5- t Bu 2( 9) and 5,6-benzo( 10), were synthesized and their structure as well as redox behavior studied by analytical, spectroscopic [ 1H, ( 13C) 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)°. The packing structure of 7 is stabilized by C–H⋯π(Ph) and O⋯O and C⋯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 PbO 2 and (NH 4) 2Ce(NO 3) 6 in MeCN and CHCl 3 generates stable phenoxyl radicals [( g ∼ 2.005 and λ ∼ 450 nm (1600–8200 M −1 cm −1)].