σ-Aromaticity in polyhydride complexes of Ru, Ir, Os, and Pt†
Transition-metal hydrides represent a unique class of compounds, which are essential for catalysis, organic synthesis, and hydrogen storage. In this work we study IrH5(PPh3)2, (RuH5(PiPr3)2)−, (OsH5(PiPr3)2)−, and OsH4(PPhMe2)3 polyhydride complexes, inspired by the recent discovery of the σ-aromatic PtZnH5− cluster anion. The distinctive feature of these molecules is that, like in the PtZnH5− cluster, the metal is five-fold coordinated in-plane, and holds additional ligands at the axial positions. This work shows that the unusual coordination in these compounds indeed can be explained by σ-aromaticity in the pentagonal arrangement, stabilized by the atomic orbitals on the metal. Based on this newly elucidated bonding principle, we additionally propose a new family of polyhydrides that display a uniquely high coordination. We also report the first indications of how aromaticity may impact the reactivity of these molecules.
- This article is part of the themed collection: Electron delocalization and aromaticity: 150 years of the Kekulé benzene structure