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(PMe 3 ) 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 [(PMe 3 ) 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 = (OCMe 2 ) 2 , cat = 1,2-O 2 C 6 H 4 , dmab = 1,2-(NMe) 2 C 6 H 4 ). By abstraction of the chlorido ligand with NaBArF (BArF = tetrakis-[3,5-bis-(trifluormethyl)-phenyl]-borat) in the presence of a neutral ligand (L = PMe 3 , MeCN, MeNC) the corresponding cationic octahedral complexes [(PMe 3 ) 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 [(PMe 3 ) 3 Rh(boryl) 2 Cl] and [(PMe 3 ) 3 Rh(boryl) 2 L] + show many similarities, their detailed structural and spectroscopic properties depend crucially on the properties of both boryl ligands.