Synthesis of Rhodaboratranes Bearing Phosphine-Tethered Boranes: Evaluation of the Metal–Boron Interaction

A series of rhodaboratranes [{o(Ph₂P)­C₆H₄}₃BRhH_n(CO)]^m (1, n = 1, m = 0; 4, n = 0, m = +1; 5, n = 0, m = −1) with different electron charges ranging from −1 to +1 have been synthesized. X-ray diffraction, IR, NMR, and DFT calculation studies have demonstrated that the σ-acceptor borane ligand produces a unique electron distribution in these systems and significantly weakens the Rh–L bond (L = CO, PR₃) trans to the boron. The reversible CO/PR₃ (R = Me or Ph) substitution reactions of 1 and 5 are attributed to these properties.