Syntheses and Applications of Indol-2-ylidene-Ligated Ruthenium-Based Olefin Metathesis Catalysts

Abstract

Ru-based catalysts bearing ambiphilic carbenes exhibit exceptionally high turnover numbers (TONs) in olefin metathesis reactions. However, the syntheses of these catalysts are still challenging because of the strong ambiphilicities of the carbenes. Herein, we prepared a family of indol-2-ylidene (IdY)-ligated Ru-based (Ru–IdY) olefin metathesis catalysts and obtained two X-ray crystal structures of Ru–IdY complexes showing a distinct conformation of the ruthenium centers. An exceptional stability of the complexes was demonstrated by a decomposition test conducted in deuterated benzene at 40 °C, indicating that approximately 98% of the most stable Ru–IdY catalyst was retained even after 3 weeks. The catalytic activities of Ru–IdY catalysts were investigated for ring-closing metathesis, ring-opening metathesis polymerization (ROMP), and ethenolysis. The most sterically accessible Ru–IdY catalyst, 2e, exhibited the best catalytic activity for ethenolysis (TON 61200 and selectivity for methyl oleate 95%; TON 53200 and selectivity for cis-cyclooctene 70%), whereas the sterically demanding catalyst 2f demonstrated the most efficient catalytic activity for ROMP in comparison to the other Ru–IdY catalysts, achieving a complete conversion in 2 min.