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

A series of rhodaboratranes [{<i>o</i>(Ph₂P)­C₆H₄}₃BRhH_<i>n</i>(CO)]^<i>m</i> (<b>1</b>, <i>n</i> = 1, <i>m</i> = 0; <b>4</b>, <i>n</i> = 0, <i>m</i> = +1; <b>5</b>, <i>n</i> = 0, <i>m</i> = −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 <b>1</b> and <b>5</b> are attributed to these properties.