Chemical Bonding Topology of Metal-Centered Polygonal Wheels: Two-Dimensional Analogues of Metallaboranes Related to Benzene and Cyclopentadienide

[Image: see text] 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.