1,3-Metal-carbon bonding predicts rich chemistry at the edges of aromatic hydrocarbons

The existence of a hitherto unrecognized 1,3-metal-carbon bond (1,3-MC bond) in particular types of transition-metal complexes is proposed using evidence from CCD X-ray structure analysis and DFT calculations. The name "edge complex" is suggested for the molecules, because the metal is coordinated at the V-shaped edges of olefinic and aromatic hydrocarbon moieties. Several edge complexes of group 4 metals have been identified from inspection of CCD data. The 1,3-MC bond is due to a d_π-p_π interaction between the metal and a β-carbon in the four-membered metallacycle region. The 1,3-MC-bonded metallacycle exhibits significant planar tetracoordinate character of the C_β atom. Moreover, the metallacycle possesses a catastrophic ring critical point (rcp) in AIM analysis, where the highest eigenvalue of the rcp exhibits a linear correlation with the M-C_β distance. The formation of hitherto unknown 1,3-MC-bonded multinuclear edge complexes of polycyclic aromatic hydrocarbons is predicted. Their electronic properties are attractive for the design of optoelectronic materials.