Aminolysis of Dicationic Ruthenium Thiophene Complexes

Dicationic sandwich complexes containing thiophene, 2-methylthiophene, 2,5-dimethylthiophene, and tetramethylthiophene react with ammonia to give salts of the formula [(ring)Ru(SC₄R₄NH₂)]X where ring = C₆Me₆ or cymene. The thiophene, 2-methylthiophene, and 2,5-dimethylthiophene complexes undergo C-S cleavage to give iminium-thiolato derivatives. In the case of the 2,5-dimethylthiophene complex, a kinetic isomer was isolated which slowly isomerized to a thermodynamic isomer. The ammonia adducts of the tetramethylthiophene complexes [(cymene)Ru(C₄Me₄S)]²⁺ and [(C₅Me₅)Rh(C₄Me₄S)]²⁺ do not undergo C-S cleavage. These 2-NH₂C₄Me₄S complexes react with protic acids to regenerate the starting dication [(ring)M(C₄Me₄S)]²⁺. The aniline adducts of thiophene, 2-methylthiophene, and 2,5-dimethylthiophene are similar to the ammonia derivatives. The structures of the kinetic isomer of [(C₆Me₆)Ru(SC₃H₂MeCHNHPh)]PF₆ and the thermodynamic isomer of [(cymene)Ru(SC₃H₂MeCMeNHPh)]OTf were established by single-crystal X-ray diffraction. The crystallographic study proves that the isomerization in this family of compounds arises from the relative configuration at the terminal carbon of the alkenyl thiolate ligand Bond distance data indicate an interaction between the iminium carbon center and the Ru atom in the kinetic isomer.