Synthesis,Structure, and Complexation of an S-Shaped Double Azahelicene with Inner-Edge Nitrogen Atoms

An S-shaped double azahelicene ( 1 ) was synthesized in excellent yield by a palladium-catalyzed double dehydrogenative C−H coupling reaction. The stereochemistry of 1 was confirmed to be dl by single-crystal X-ray diffraction analysis. Selective formation of dl- 1 was attributed to the isomerization of the kinetically controlled product (meso- 1 ) into the more thermodynamically stable dl- 1 under the applied reaction conditions. dl- 1 can coordinate to palladium(II) in a bidentate trans-chelating fashion, which was confirmed by X-ray absorption fine structure (XAFS) as well as by X-ray photoelectron spectroscopy (XPS), diffuse reflectance (DR) UV/Vis, and far-infrared (FIR) absorption spectroscopy. Theoretical calculations of palladium complex 16 revealed a weak attractive interaction between palladium and carbon atoms on the central dimethoxynaphthalene core, which could facilitate a disproportionation between a trans-chelating (dl- 1 ) ⋅ PdCl₂ complex and PdCl₂ to form 16 .