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 a 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 calculation of palladium complex  16  was revealed a weak attractive interaction between a palladium and carbon atoms on the central dimethoxynaphthalene core, which could facilitate a disproportionation between a trans-chelating ( dl - 1 ) · PdCl 2 complex and PdCl 2  to form  16 .