PI-FACIAL SELECTIVITIES IN THE COORDINATION OF AN OPTICALLY PURE FUSED CYCLOPENTADIENYL LIGAND TO ARENE RUTHENIUM MOIETIES - NMR SPECTRAL AND STRUCTURAL CHARACTERIZATION OF A SINGLE DIASTEREOMER OF [(PCP)RU(ME6C6)]PF6

Optically pure thallium 9,9-dimethyltricyclo[6.1.1.0(2,6)]deca-2,5-die nide (TlPCp) reacts with [(eta6-ar-ene)RuCl2]2 (arene = C6H6, MeC6H5, p-MeC6H4CHMe2, Me6C6) and NH4PF6 to form two isomers of the complexes [(eta5-PCp)Ru(eta6-arene)]PF6. The pi-facial stereoselectivity for coo rdination of PCp is a function of the steric bulk of the arene increas ing from a 1:1 (C6H6) to a 14:1 (Me6C6) exo/endo isomer ratio. New com plexes were characterized by elemental analyses, physical properties, differential pulse voltammetry and H-1 and C-13{H-1} one-and two-dimen sional NMR spectroscopy. The structure of [(eta5-PCp)Ru(eta6-Me6C6)]PF 6 was confirmed by X-ray crystallography. This compound crystallized i n the acentric space group C222(1) in a unit cell with the following d imensions: a = 11.451(4), b = 13.426(5), c = 31.249(3) angstrom, V = 4 804(3) angstrom3, Z= 8. Refinement converged to R(F) = 0.056 for 1723 independent observed (I > 3sigma(I)) reflections. Ruthenium coordinate s to the less sterically hindered exo face of the PCp ligand, anti to the gem-dimethyl group, and is closer to the arene (Ru-ring centroid = 1.73 angstrom) than to the PCp ligand (Ru-ring centroid = 1.79 angstr om).