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 Cp ₂Rh₂(BO)_n structures resemble to a certain extent the previously studied isoelectronic cyanide complexes Cp ₂Rh₂(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.