Three-Bladed Molecular Propellers: Design of Fluxional and Aromatic MB ₁₀ O ₁₀ – (M = Tc, Re) Clusters

Single-molecule nanorotors based on boron clusters often suffer from a trade-off between dynamic fluxionality and chemical stability. Herein, we extend our design strategy beyond the previously reported “ballet rotor” to its heavier group 7 congeners, technetium and rhenium. Through a comprehensive computational exploration, we identify the global minimum (GM) structures of MB10O10– (M = Tc, Re) as pyramidal clusters with the structural formula [(OB)3–M©B7O7]−, featuring a (BO)3 cap on one side of a B7O7 ring, resembling a three-bladed molecular propeller. Molecular dynamics simulations confirm the ultrafast, nearly barrierless rotation of the (BO)3 unit around the molecular axis. Remarkably, these fluxional clusters exhibit exceptional stability, with large HOMO–LUMO gaps (6.09–6.10 eV) and high vertical detachment energies (VDEs) (5.36–5.37 eV). Chemical bonding and nucleus-independent chemical shift (NICS) analyses reveal that the stability originates from a σ + π + δ triple aromaticity within the MB10 core, while the delocalized bonding also acts as a “lubricant” enabling free rotation. These triply aromatic molecular propellers represent a new, robust class of nanoscale rotors with promising potential for molecular machinery.