Aromaticity of metal acetylacetonates and a Möbius chelate of a cadmium(II) complex of an N4 helical ligand

Abstract

Interaction of a benzene C–H tip with a metallacycle of various metal acetylacetonates are studied by means of DFT calculations at M062X/LanL2DZ and M062X/6-311++G(2d,p) levels. It is concluded that an angular interaction with a tilt angle θ of the C–H tip is diagnostic of aromaticity of a chelate ring in a metal acetylacetonate. Larger the θ value, the more aromatic is the probed molecule. This finding is supported by the known X-ray crystal structure of bis(acetylacetonato)platinum(II)-benzene. Acetylacetonate anion has 6 π electrons fulfilling Hückel’s 4n+2 rule for aromaticity. A thirteen membered 12 π electron chelate ring in a cadmium(II) complex of a helical N4 ligand is shown to be aromatic by establishing it as a Möbius object.