C4-Symmetric Bowl-Shaped Diruthenium Tetracarboxylate Catalysts for Enantioselective C–H Functionalization Using Donor/Acceptor Carbenes

Cationic diruthenium (II,III) tetracarboxylate catalysts have been shown to catalyze selective intermolecular C-H functionalization reactions using donor/acceptor carbenes in high yield and with high levels of enantioselectivity. The diruthenium catalysts were compared to the analogous dirhodium (II,II) tetracarboxylate and showed similar levels of enantioselectivity for most reactions. A distinctive feature of the diruthenium catalysts is a greater preference for C-H functionalization over cyclopropanation compared to the corresponding dirhodium catalysts. Also, the diruthenium catalysts have a greater preference for sterically more accessible sites compared with their dirhodium counterparts. These studies show that the diruthenium catalysts are generally effective catalysts for enantioselective intermolecular C-H functionalization, but further optimization would be needed for them to match the dirhodium catalysts in terms of functional group compatibility, turnover frequency, and turnover numbers.