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X-Ray Analysis of Intermediates and Products Involved in Solid-State C-H Bond Activation by Pd(II) Chloride Precoursors

C–H bond activation is often the first step in metal-catalyzed functionalization of the organic compounds usually performed using palladium (Pd) catalysts. Number of reports on successful solid state C–H bond functionalization by ball milling is growing, but no deeper insight into their mechanism has been obtained. Recently, a detailed mechanistic study of the solid-state activation of two C–H bonds in an asymmetric azobenzene substrate by Pd(II) chloride precursors, e.g. PdCl2 and PdCl2(MeCN)2, has been elucidated using in situ collected Raman spectra and ex situ spectroscopic and synthetic experiments. Results support a regioselective two-step reaction in which each step involves a coordination of the substrate to the Pd(II) precursor forming an adduct that then undergoes the C–H bond cleavage. Herein we report single- crystal X-ray diffraction experiments that allowed for structural identification of the azobenzene reactant as well as reaction intermediates and products of the double C–H bond activation in the solid state (Figure 1). Structural analysis proved as a key step toward determination of the reaction course and supported the proposed mechanism of the C–H bond activation in the azobenzene substrate, which was found analogous to the proposed mechanism for these reactions in solution.

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

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