Synthesis, characterization, redox behavior and hydrogenation catalytic activity of bis(<i>N</i>-aryl-3, 5-Bu<i><SUP>t</SUP></i>₂-salicylaldiminato)palladium(II) complexes

Abstract

The synthesis, spectroscopic (H-1 NMR, IR, UV-Vis), electron-transfer properties and catalytic reactivity of new palladium(II) complexes, with N-aryl-3,5-Bu-2(t)-salicylaldimines prepared from 3,5-Bu-2(t)-salicylaldehyde and o-,p-substituted anilines (X-C6H4NH2, X = H. F. Cl, Br, CH3, OCH3, t-Bu, 5,6-benzo) are reported. Cyclic voltammetry studies of the complexes exhibit an irreversible anodic peak that corresponds to the phenoxide/phenoxyl oxidation. The chemical oxidation of the complexes with (NH4)(2)Ce(NO3)(6) in CHCl3, besides relatively stable Pd-II-phenoxyl radical complexes (g = 2.0083-2.0114), also generate nitroxide radicals exhibiting strongly anisotropic spectra (g(parallel to) = 2.0061, g(perpendicular to) = 2.0072, A(parallel to) = 37.5, A(perpendicular to) = 5.38 G) typical for immobilized nitroxide radicals. It has been found that the introduction of t-Bu groups on the salicylic ring increases catalytic activity of towards hydrogenation of nitrobenzene in DMF at room temperature. (C) 2004 Elsevier Ltd. All rights reserved.