Ligand properties of boryl ligands in bis-boryl rhodium(iii) complexes: a case study

The oxidative addition of five diborane(4) derivatives, symmetrical and unsymmetrical, to [Rh(PMe3)(3)Cl] was studied. Only for the more electron poor diboron derivatives, B(2)cat(2), B(2)pin(2) and catB-Bpin the resulting octahedral bis-boryl complexes [(PMe3)(3)Rh(boryl)(2)Cl] were obtained, while for the more electron rich congeners only the equilibrium oxidative addition (catB-Bdmab) or no significant reaction (pinB-Bdmab) was observed (pin = (OCMe2)(2), cat = 1,2-O2C6H4, dmab = 1,2-(NMe)(2)C6H4). By abstraction of the chlorido ligand with NaBArF (BArF = tetrakis-[3,5-bis-(trifluormethyl)-phenyl]-borat) in the presence of a neutral ligand (L = PMe3, MeCN, MeNC) the corresponding cationic octahedral complexes [(PMe3)(3)Rh(boryl)(2)L](+) were obtained. All isolated complexes were fully characterised including single crystal X-ray diffraction and heteronuclear, temperature dependent NMR spectroscopy. Whilst the complexes [(PMe3)(3)Rh(boryl)(2)Cl] and [(PMe3)(3)Rh(boryl)(2)L](+) show many similarities, their detailed structural and spectroscopic properties depend crucially on the properties of both boryl ligands.