Contribution to the chemistry of metal complexes with stereogenic metal centers: Diastereoselective formation of ruthenium half-sandwich complexes

The chiral half-sandwich complexes 3 and 4 are formed with high diastereose lectivities in the reaction of cyclopentadienides 2a,b, bearing tethered ph osphaferrocene donor moieties with planar chirality, and [(PPh3)(3)RuCl2] i n toluene at 90 degreesC. The diastereoisomers of the Cp complex 3 are obta ined in a 95:5 ratio, whereas for the Cp* derivative 4 only one isomer is d etectable, the structure of which has been determined by X-ray diffraction. Substitution of the chloride ligand in 4 by other anionic (H-, I-) or neut ral (H-2, py) ligands proceeds stereospecifically in all cases. In contrast , conversion of the chlorides 3a,b (95:5) to the respective hydrides 9a,b p roceeds with complete epimerization at Ru. In CHCl3 the 1:1 mixture of hydr ides 9a,b is reconverted to the chlorides to give a kinetically controlled 4:1 mixture of isomers 3a,b. Equilibration of this mixture in toluene at 90 degreesC restores the original ratio of isomers of 95:5, which we therefor e believe to reflect the thermodynamically controlled value. The cationic H -2 complex 7, generated via Cl abstraction from 4 in the presence of Hz, wa s characterized to be a eta (2)-dihydrogen complex by measuring the T-1 val ue of the coordinated H-2 ligand.