Optical Resolution of π-Thiophene Complexes (C₆Me₆)Ru(2-RC₄H₃S)²⁺and Related Studies

Abstract

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 (−)-9kin, which isomerized to (+)-9therm 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.