Oligounsaturated Five‐Membered Carbocycles – Aromatic and Antiaromatic Compounds in the Same Family

Abstract

Most compounds containing oligounsaturated five-membered carbocycles ranging from cyclopentadiene to C 20 fullerene display interesting electronic and structural properties. This chapter describes recent developments in this area, starting with stabilized cyclopentadienyl cations, then discusses several fulvenes as well as spiroannelated cyclopentadiene derivatives and eventually linearly as well angularly fused oligocyclic five-membered ring systems. Among these oligounsaturated di-, tri-, and oligoquinanes, the features of the rather unstable pentalene and acepentalene are discussed with respect to their generation and electronic ground states. Structural properties, including those of the stable dilithium diides as well as several metal complexes are presented. Finally, the generation and characterization of the highly unstable C 20 fullerene, which sets a new benchmark for this class of molecules, are highlighted. 2.1