First Structure Analysis and Photoelectron Spectroscopic Investigation of an Azete and an Azete‐Cobalt Complex

The antiaromatic 2,3-ditert-butyl-4-mesityl axete 1 exists in the crystal only as the valence isomer 1A. The four-membered ring has the structure of a distorted rectangle, and the interplanar angle between the aromatic and antiaromatic rings is 70°. The valence isomer 1B participates to at most 5% in an equilibrium (13C NMR). In contrast, the bond lengths in the four-membered ring are almost equal in the azete-cobalt complex 2 because of electron delocalization.