Highly Diastereoselective Preparation of Ruthenium Bis(diimine) Sulfoxide Complexes: New Concept in the Preparation of Optically Active Octahedral Ruthenium Complexes

Abstract

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 (73−76% de). Stereochemistry at the metal center for the major isomer was determined by X-ray study of [Ru(bpy)2(dmbpy)]·2PF6, 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 Δ-7 (major isomer) revealed the presence of two intramolecular interactions, oxygen−hydrogen interaction and π−π stacking of the pyridyl−tolyl rings, while the structural analysis of Δ-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)2Cl2] with (R)-(+)-methyl p-tolyl sulfoxide, which gave, in acetonitrile, the complex cis-[Ru(2,9-dimethyl-1,10-phenanthroline)2(CH3CN)2]·2PF6, 10. Oxygen−hydrogen and π−π interactions are used to explain both the reactivity of cis-[Ru(diimine)2Cl2] with the sulfoxide and the stability of the major isomer when enantiomerically pure sulfoxide was used.