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X-Ray Identification and Characterization of Azobenzene Palladacycles Obtained by Solid- State C–H Bond Activation

Cyclopalladated complexes or palladacycles are successfully applied in many areas of material science and biological chemistry. Their preparation is usually performed in solution but number of reports on the solid-state synthesis of these organometallic complexes is steadily growing. Recently, our group reported a successful solid-state synthesis of azobenzene palladacycles in a ball mill that was followed by a detailed mechanistic study of C–H bond activation in azobenzene by various palladium (Pd) precursors, i.e. polymeric PdCl2, monomeric [PdCl2(MeCN)2], trimeric [Pd(OAc)2]3 and ionic [Pd(MeCN)4][BF4]2. Herein we report on X-ray diffraction identification and characterization of palladacycles obtained by C–H bond activation in 4-chloro-4’-(N, N- dimethylamino)azobenzene by various Pd(II) precursors in a ball mill (Figure 1). Each type of the employed Pd(II) precursor afforded a structurally different mono- and/or dipalladated complex. Structural analysis shows that all monopalladated products have a palladated p-(N, N-dimethylamino)phenyl ring, which agrees with a regioselective solid- state reaction. Reactions with acetate and chloride Pd(II) precursors afford dimeric and monomeric dicyclopalladated complexes, respectively. Obtained results show a strong influence of the ancillary ligands on the molecular structure of the analyzed palladacycles and support the proposed mechanistic scheme for double palladation of azobenzenes in a ball mill by various Pd(II) precursors.

X-Ray analysis ; palladium ; organometals ; C-H bond activation ; mechanism

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