Optically Active Ortho-Metalated Half-Sandwich Ruthenium Complexes: Solid-State NMR as a Convenient Tool To Analyze Mixtures of Diastereomers

Bulk solid samples of various ratios of the cyclometalated arene ruthenium diastereomers (S)Ru- and (R)Ru-[(η6-C6H6)Ru(C6H4-2-(R)-CH(Me)NMe2)PMe2Ph]+PF6- (3a/3b), of which the configurational stability at the metal
center has been established by classical solution techniques, have been analyzed by the 13C cross-polarization
magic angle spinning (CP-MAS) and 31P MAS NMR. The spectra obtained allowed us to detect both isomers and
to estimate their respective proportions by 31P spectra. This technique was applied to a bulk solid sample of the
diastereomers (S)Ru- and (R)Ru-[(η6-C6H6)Ru(C6H4-2-(R)-CH(Me)NMe2)NCMe]+PF6- (1a/1b), which were shown
to be configurationally labile by classical solution experiments. Detection of isomer 1a only in the resulting 13C
CP-MAS NMR spectrum demonstrated that there has been epimerization of 1b to 1a during crystallization, thus
confirming the configurational lability at the metal center.