Abstract
The anion [Au@Ru(5)(CO)(15)(μ-CO)(4)](-) has a pentagonal wheel structure that can be derived from a hypothetical pentagonal ruthenium carbonyl cluster Ru(5)(CO)(20) by insertion of a gold atom in the center, thereby splitting the original Ru(5) pentagon in Ru(5)(CO)(20) into five AuRu(2) triangles. The six electrons used to form 3c-2e bonds in three of the five AuRu(2) triangles suggest a relationship to the aromatic sextet of the likewise pentagonal cyclopentadienide anion. Furthermore, the pentagonal wheel framework of [Au@Ru(5)(CO)(15)(μ-CO)(4)](-) can be derived from a pentagonal bipyramid, such as that found in the deltahedral borane anion B(7)H(7)(2-), by bringing the two C(5) axial vertices together at the center of the equatorial pentagon. Similarly, the hexagonal wheel complexes Ni@P(6)R(6) and Pd@Pd(6)(μ-N═CtBu(2))(6) with six triangular faces can be derived from a hexagonal bipyramid, such as that found in the dirhenaborane (η(5)-Me(5)C(5))(2)Re(2)B(6)H(4)Cl(2), by bringing the two C(6) axial vertices together at the center of the equatorial hexagon. A reasonable chemical bonding model for the hexagonal wheel complexes has three-fold symmetry with 3c-2e bonds in three of these six triangular faces analogous to the C═C double bonds in a Kekulé structure of benzene.