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)]BF4 and [Ru(indole)(2)](BF4)(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 C-13,H-1 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.