Highly diastereoselective preparation of ruthenium bis(diimine) sulfoxide complexes:: New concept in the preparation of optically active octahedral ruthenium complexes

Microwave irradiation of racemic cis-[Ru(bpy)(2)(Cl)(2)] (bpy = 2,2'-bipyridine) or racemic cis[Ru(phen)(2)(Cl)(2)] (phen phenanthroline) with either (R)-(+)- or (S)-(-)-methyl p-tolyl sulfoxide yielded the ruthenium bis(diimine) sulfoxide complexes with a high level of asymmetric induction (13-76% de). Stereochemistry at the metal center for the major isomer was determined by X-ray study of [Ru(bpy)(2)(dmbpy)]. 2PF(6), obtained by reaction of complex 3 with 4,4'-dimethyl-2,2'-bipyridine and confirmed by X-ray study of the complex 7. The absolute configuration at the metal center for the minor isomer was established by X-ray study of the minor isomer derived from the reaction of cis-[Ru(bpy)(2)(Cl)(2)] with (S)-(-)-methyl p-tolyl sulfoxide. Structural analysis of Delta-7 (major isomer) revealed the presence of two intramolecular interactions, oxygen-hydrogen interaction and pi-pi stacking of the pyridyl-tolyl rings, while the structural analysis of Delta-5 (minor isomer) showed only the presence of the oxygen-hydrogen interaction. The importance of these interactions in this transformation was confirmed by the reaction of cis-[Ru(2,9-dimethyl-1,10-phenanthroline)(2)Cl-2]with (R)-(+)-methyl p-tolyl sulfoxide, which gave, in acetonitrile, the complex cis-[Ru(2,9-dimethyl-1,10-phenanthroline)(2)(CH3CN)(2)]. 2PF(6), 10. Oxygen-hydrogen and pi-pi interactions are used to explain both the reactivity of cis-[Ru(diimine)(2)Cl-2] with the sulfoxide and the stability of the major isomer when enantiomerically pure sulfoxide was used.