Optical resolution of π-thiophene complexes (C₆Me₆)Ru(2-RC₄H₃S)²⁺ and related studies

Diastereomeric iminium thiolato complexes were prepared by the addition of S-(-)-α-methylbenzylamine to the π-thiophene complexes [(C₆Me₆)Ru(2-RC₄H₃S)]²⁺, where R = Me (1²⁺), CH₂OH (3²⁺), and 2-C₄H₃S (6²⁺). After chromatographic separation, the diastereomers were treated with HOTf to generate optically pure π-thiophene complexes. The absolute configuration of [(C₆Me₆)RuSCMeC₂H₂(CHNHCHMePh)]OTf, (-)-2(OTf), was determined by a single-crystal X-ray diffraction; the monohydrate crystallized in the acentric space group P2₁2₁2₁. Acetone solutions of (-)-1²⁺ and (-)-3²⁺ are optically stable for days in solution (25°C), while the bithiophene complex was unstable with respect to dissociation of the bithiophene ligand. Optical resolution of [(cymene)Os(2-MeC₄H₃S)](OTf)₂ was not possible due to the instability of the iminium thiolato. Base hydrolysis of (-)-1²⁺ gave the formyl thiolato complex (-)-9_kin, which isomerized to (+)-9_therm with inversion of configuration at Ru, as indicated by circular dichroism measurements. The methyl ester of the amino acid (L)-phenylalanine was shown to add to (C₆Me₆)Ru(C₄H₄S)²⁺ to give a 2:1 mixture of diastereomeric iminium thiolato complexes.