Chiral and achiral recyclable ruthenium-based metathesis catalyst.

摘要

Chapter 1. After the unexpected discovery of an internal oxygen chelated Ru-based metathesis catalyst, a more highly active complex was synthesized by substituting the phosphine ligand with a N-heterocyclic carbene. This new ligand greatly enhances the reactivity and stability of recyclable metathesis catalyst allowing for the ring-closing metathesis of more sterically demanding substrates and allowing for the synthesis of cis olefins. To further improve on the catalysts recycling strategy, the complex was attached to a dendrimer, which offered the advantage of being more readily isolable by the increased polarity. By taking advantage of the minor chemical shift difference for the carbene proton signals of the dendritic and monomeric catalyst, a metal cross over experiment was conducted that gave substantial evidence for the release-return mechanism.; Chapter 2. Chiral variant Ru-catalyst was synthesized and studied. The synthesis included a novel diastereoselective ligand substitution. The air-stable bidentate complex was found to be recyclable and stereogenic at the Ru center, however, less active than the parent complex. Despite the lower reactivity, chiral complex catalyzes selected ring-opening/cross metathesis reactions in good to excellent selectivities (80--96% ee).; Chapter 3. Steric and electronic alterations were made on the original chiral catalyst and the catalytic activities were compared. The findings revealed that the steric modification had the largest effect by increasing reactivity >100 times higher. This allows for efficient asymmetric ring-opening and ring-closing metathesis that cannot by performed by the parent chiral complex. Preliminary mechanistic investigations have also given some insight to the activity differences.