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

A series of rhodaboratranes [{o(Ph2P)­C6H4}3BRhHn(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.