Novel 1,2-Binaphthyl-tethered closo-Rhodacarborane: Synthesis, Structure and Catalytic Applications

Carboranes are noted for their three-dimensional aromaticity and exceptional stability. Their partially deboronated derivative, the nido-dicarbollide anion, serves as an analog of the cyclopentadienyl ligand, forming metallacarboranes with potential in catalysis and materials science. However, the application of such complexes in homogeneous catalysis remains largely underexplored. This work reports the synthesis and crystal structure of a novel binaphthylene-bridged closo-rhodacarborane complex, μ-1,2-[(CH₂)₂C₂₀H₁₂]-3-(η³-C₈H₁₃)-3,1,2-closo-RhC₂B₉H₉ (6), and its ligand precursor μ-1,2-C₂₀H₁₂(CH₂)₂-1,2-closo-C₂B₁₀H₁₀ (4).
The structures of compounds 4 and 6 were fully characterized by single-crystal X-ray diffraction, high-resolution mass spectrometry, infrared spectroscopy, and NMR. Crystallographic analysis of 6 reveals a unique exo-polyhedral agostic C–H···Rh interaction, along with a network of intra- and intermolecular noncovalent interactions, including intramolecular C–H···π, and intermolecular C–Cl···π, C–H···π, C–H···H–B, and C–H···H–C contacts. In the crystal lattice of compound 4, significant intermolecular B–H···π and C–H···H–B interactions are observed. These weak interactions are crucial for understanding the solid-state packing and stability of these molecules.
Preliminary catalytic studies demonstrate that complex 6 acts as a well-defined Rh(III) catalyst. It exhibits high activity at low loadings in selective cyclopropanation, epoxidation, C–H insertion, and Curtius-type rearrangement reactions under mild conditions. This work provides a new molecular prototype for crystal engineering and the design of catalytic materials based on metallacarboranes.