Synthesis, Characterization, Redox Behavior and Hydrogenation Catalytic Activity of Bis(n-Aryl Palladium(II) Complexes

Abstract

The synthesis, spectroscopic (1H NMR, IR, UV-Vis), electron-transfer properties and catalytic reactivity of new palladium(II) complexes with N-aryl-3,5-Bu2t-salicylaldimines prepared from 3,5-Bu2t-salicylaldehyde and o-,p-substituted anilines (X-C<inf>6</inf>H <inf>4</inf>NH<inf>2</inf>, X = H, F, Cl, Br, CH<inf>3</inf>, OCH<inf>3</inf>, 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 (NH<inf>4</inf>) <inf>2</inf>Ce(NO<inf>3</inf>)<inf>6</inf> in CHCl<inf>3</inf>, besides relatively stable PdII-phenoxyl radical complexes (g = 2.0083-2.0114), also generate nitroxide radicals exhibiting strongly anisotropic spectra (g<inf>∥</inf> = 2.0061, g<inf>⊥</inf> = 2.0072, A <inf>∥</inf> = 37.5, A<inf>⊥</inf> = 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. © 2004 Elsevier Ltd. All rights reserved.