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 ciscyclooctene 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.

Synthesis and Application of Robust Spiro [Fluorene 9] CAAC Ruthenium Alkylidene Complexes to the „One-Pot“ Conversion of Allyl Acetate to Butane-1,4-diol

“…An important aspect of the ruthenium alkylidene CAAC complexes is the rotation of the CAAC ligand over the Cl2Rualkylidene plane. [44][45][46] As indicated by the 1 H and nOe NMR measurements, no dynamic behavior was observed in case of complexes 6a and 6d at room temperature. While the CAAC ligands of complexes 6b and 6c appear to rotate along the Ru-CCAAC bond at similar condition.…”

“Inverted” Cyclic(Alkyl)(Amino)Carbene (CAAC) Ruthenium Complex Catalyzed Isomerization Metathesis (ISOMET) of Long Chain Olefins to Propylene at Low Ethylene Pressure

“…Just by changing the N aryl group from DEP (2,6diethylphenyl, free rotation at RT) to DIPP (2,6diisopropylphenyl, frozen around Ru‐C CAAC bond at RT) or utilizing cyclohexyl group as R’ instead of phenyl, the fluxionality of the complexes and the thermodynamics of syn and anti ‐isomers were significantly affected. To date only a handful N alkyl substituted CAAC ruthenium metathesis catalysts were described, [ 24 , 27 ] despite the number of potential N alkyl carbene precursor salts known in the literature. [ 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 ] As expected, replacing the N aryl substituents to N alkyl groups caused significant shift in the stability of different rotamers and the fluxionality of the Ru‐C CAAC bond compared to the above‐mentioned examples.…”

“…Some additional chiral N ‐alkyl substituted CAAC‐Ru complexes exhibiting inverted structure have recently been reported by Cramer, Hong and Lee (Scheme 1 ). [ 24 , 27 ] In our presenet work, we have synthesized a wide range of latent N ‐alkyl CAAC‐Ru complexes showing inverted geometry. In these complexes, the N ‐alkyl groups are not only oriented on the opposite side to Ru = CHR but they show a non‐dynamic behavior as well.…”