MeO-Biphep and Binap Ligands as Six-Electron Donors to Ruthenium(II). X-ray and NMR Studies on Cp-, Pyrrole-, and Indole-Derived Complexes

Ru(II) complexes of the chiral ligands Binap and MeO-Biphep containing six-electron hydrocarbon donors, such as Cp, a deprotonated pyrrole, or the benzene ring of indole, attain the 18-electron configuration by complexing a proximate biaryl double bond. The solid-state structures for two of these, [RuCp( 2 )]BF 4 and [Ru(indole)( 2 )](BF 4 ) 2 ( 2 = (6,6‘-dimethoxybiphenyl-2,2‘-diyl)bis(bis(3,5-di- tert -butylphenyl)phosphine)), have been determined by X-ray diffraction. They reveal that a biaryl double bond, immediately adjacent to one P-donor, coordinates to the ruthenium, thus making the chelating ligand a six-electron donor. The double bonds remain coordinated in solution as shown by HMBC 13 C, 1 H long-range correlation spectroscopy. However, 2-D NMR exchange spectroscopy suggests that the biaryl double bond is weakly coordinated since the two halves of the C 2 -symmetric Binap (or MeO-Biphep) ligands are in slow exchange at ambient temperature.