Dynamic Structural Fluxionality in a Planar Tetracoordinate Carbon Cluster Stabilized by Boron Ligands

• Published in: Chemistry : a European journal Vol. 30; no. 51; pp. e202402132 - n/a
• Main Authors: Jin, Bo, Wang, Zai‐Ran, Yan, Miao, Feng, Lin‐Yan, Miao, Chang‐Qing, Wang, Ying‐Jin
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 11.09.2024
• Subjects: Atomic properties; Atomic structure; Boron; Boron cluster; Carbon; Chemical bonds; Clusters; Covalent bonds; Double aromaticity; Dynamic fluxionality; Dynamic structural analysis; Electronic structure; Global minimum; Ligands; Molecular machines; Planar tetracoordinate carbon; Rotors; Boron cluster; Global minimum; Dynamic fluxionality; Planar tetracoordinate carbon; Double aromaticity
• ISSN: 0947-6539; 1521-3765; 1521-3765
• DOI: 10.1002/chem.202402132

The design of boron‐based molecular rotors stems from boron‐carbon binary clusters containing multiple planar hypercoordinate carbons (phCs, such as C2B8). However, the design of boron‐coordinated phCs is challenging due to boron's tendency to occupy hypercoordinate centers more than carbon. Although this challenge has been addressed, the designed clusters of interest have not exhibited dynamic fluxionality similar to that of the initial C2B8. To address this issue, we report a σ/π doubly aromatic CB2H5+ cluster, the first global minimum containing a boron‐coordinated planar tetracoordinate carbon atom with dynamic fluxionality. Dynamics simulations show that two ligand H atoms exhibit alternate rotation, resulting in an intriguing dynamic fluxionality in this cluster. Electronic structure analysis reveals the flexible bonding positions of the ligand H atoms because they do not participate in π delocalized bonding nor bond to any other non‐carbon atom, highlighting this rotational fluxionality. Unprecedentedly, the fluxional process involves not only the usual conversion of the number of bonding atoms, but also the type of bonding (3c π bonds ↔4c σ bonds), which is an uncommon fluxional mechanism. The cluster represents an effort to apply phC species to molecular machines. We reported a molecular compasses CB2H5+ with a planar tetracoordinate carbon (ptC) atom, two ligand hydrogen atoms attached to the carbon rotate alternately. This is the first global minimum for boron‐coordinated ptC clusters with dynamic fluxionality.