title: Isolation of planar four-membered aromatic systems by using confined spaces of cobalt pentaaryl[60]fullerene complexes.
abstract: As a new class of neutral closed-shell aromatic four-membered ring systems, CoE(3) (E = S, Se) was constructed inside the bowl-shaped space of pentaaryl[60]fullerene. X-ray crystallographic analysis of CoS(3)(η(5)-C(60)Ar(5)) revealed that the CoS(3) unit is planar, and DFT calculations suggested an aromatic 6π-electron system. Steric protection by the pentaaryl[60]fullerene ligand is critical for isolation and characterization of the aromatic hetero cobaltacyclobutane. Unique reactivity of the CoS(3) unit was demonstrated by disruption of 6π-conjugation with abstraction of the sulfur atom, affording a dimer, [CoS(2)(η(5)-C(60)Ar(5))](2). This work provides new insight into the aromaticity of four-membered ring systems and advances the understanding of aromatic organometallic compounds.
authors.affiliation: Department of Chemistry, The University of Tokyo, Hongo, Tokyo 113-0033, Japan.
authors.forename: Masashi
authors.initials: M
authors.lastname: Maruyama
authors.forename: Jing-Dong
authors.initials: JD
authors.lastname: Guo
authors.forename: Shigeru
authors.initials: S
authors.lastname: Nagase
authors.forename: Eiichi
authors.initials: E
authors.lastname: Nakamura
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Matsuo