Theoretical Studies on Organic Catalysis: N-Heterocyclic Carbene Catalyzed Ring-Opening Polymerization and Initiation of Z-selective Olefin Metathesis with Ruthenium Catalysts
- Author(s): Dong, Xiaofei
- Advisor(s): Houk, Kendall N
- et al.
The mechanism of NHC catalyzed ring-opening polymerization of lactide and the factors controlling the reactivities of photoswitchable NHC catalysts have been investigated with the DFT method. The general base mechanism is favored comparing to the nucleophilic mechanism for the ring-opening polymerization of lactide catalyzed by NHC. The reactivities of the NHC catalysts are determined by their electrophilicities. The NHCs which are highly electrophilic form adducts in the presence of alcohol. These mechanistic studies will help the design of novel multifunctional catalysts.
The initiation mechanism of Z-selective ruthenium catalysts and the effects of anionic ligands on the initiation rates are studied with DFT calculation. The dissociative pathway is favored for the initiation and the metallacyclobutane cycloreversion is the rate determining step. Catalysts with more steric bulk and less nucleophilic ligands have higher initiation rates because of the structural differences between the precatalyst and the transition state.