π-Complexation of Post-Transition Metals by Neutral Aromatic Hydrocarbons: The Road from Observations in the 19th Century to New Aspects of Supramolecular Chemistry

Compounds of the elements in the three triads of post-transition metals, Ga−In−Tl, Ge−Sn−Pb, and As−Sb−Bi, form in their low-valence states a variety of stable complexes with neutral hydrocarbons. This chemistry is reviewed starting from the early discoveries in the 19th century and including the most recent contributions.