Preparation of Imidazolium Ion Functionalized HG-II Chiral Ruthenium Catalysts and Their Catalytic Performance in Asymmetric Olefin Metathesis

The yield and stereoselectivity of the ruthenium-catalyzed olefin metathesis reaction are mainly determined by the nature of the ligands. In this study, two chiral HG-II ruthenium catalysts with imidazolium ion functionalized Hoveyda ligands were prepared, and their activity and stereoselectivity in the symmetric ring-closure metathesis (ARCM) and asymmetric ring-opening cross-olefin metathesis (AROCM) reactions were investigated. The results show that the modification of the Hoveyda ligands by ionic functional group produced no significant effect on ARCM reaction. For AROCM reaction, the ionic modification of the Hoveyda ligands shows an obvious improvment on both the E/Z selectivity and ee value for some products. Therefore, in the AROCM reaction, the Hoveyda ligands modified with imidazolium ion can be considered as a means to improve the stereoselectivity of the reaction.