The versatility of the boronyl ligand in binuclear cyclopentadienylrhodium derivatives

Density functional theory predicts the chemistry of the binuclear cyclopentadienylrhodium boronyls Cp2Rh2(BO)n (n = 4, 3, 2) derivatives to be considerably more complicated than that of the related cyclopentadienylrhodium carbonyls Cp2Rh2(CO)n owing to the greater variety of BO coordination modes in energetically competitive structures. In this connection, the Cp2Rh2(BO)n structures resemble to a certain extent the previously studied isoelectronic cyanide complexes Cp2Rh2(CN)n. All of the energetically low-lying Cp2Rh2(BO)n structures prefer coaxial geometries with terminal Cp rings and bridging BO groups. By considering the bridging BO groups as neutral ligands, both one-electron donor bridging μ-BO groups bonded to the Rh atoms exclusively through their B atoms and three-electron donor η2–μ-BO groups bonded to the Rh atoms through both their B and O atoms are found in low energy structures. The three-electron donor bridging η2-μ-BO groups exhibit longer B–O distances and lower ν(BO) frequencies than their one-electron donor bridging μ-BO counterparts. The thermodynamic stabilities predicted for the binuclear Cp2Rh2(BO)n derivatives suggest them as possible synthetic objectives.

Graphical abstractThe energetically low-lying Cp2Rh2(BO)n structures (n = 4, 3, 2) prefer coaxial geometries with terminal Cp rings and bridging BO groups. Both one-electron donor bridging μ-BO groups and three-electron donor η2-μ-BO groups bonded to the Rh atoms through both their B and O atoms are found in these structures.Figure optionsDownload full-size imageDownload as PowerPoint slide