Olefin metathesis (OM) is a powerful and versatile method to form C-C double bonds. The three major categories of this process are ring-opening metathesis (ROM), ring-closing metathesis (RCM), and cross-metathesis (CM). While this process is taking place, degenerate results can often occur, meaning that the starting material is regenerated as a product of the metathesis reaction. In industrial settings, olefin metathesis is utilized to produce propylene and linear α-olefins, which are used to produce more complex compounds like plastics and detergents. Unproductive metathesis has applications in isotope labeling, which is useful for the pharmaceutical industry. The most used and well-known catalysts for metathesis are made with relatively rare and difficult to mine transition metals Ru, Mo, and W. Vanadium, being more abundant in the earth's crust, is a cost-effective and greener alternative. Additionally, new reactivity can be found while exploring vanadium catalysis. <br/>The most studied reactions employing vanadium catalysts focus on their ability to catalyze ring-opening metathesis polymerization (ROMP) of norbornene, like those of the Nomura group. These compounds have limited activity in the metathesis of acyclic olefins. Our lab recently synthesized complexes with varying imido groups and neutral ligands that were found to be active to RCM of several dicrotyl compounds containing different functional groups. However, synthesized catalysts quickly decompose in the presence of ethylene (a byproduct of the catalysis reaction) which leads to low productivity in RCM involving terminal dienes.  <br/>To improve stability towards ethylene, iMes-NHC (N-heterocyclic carbene) was found to be an effective replacement for the phosphine as a neutral ligand because of its increased capabilities as a σ-bond donor and its bulky size that sterically hinders bimolecular degradation. This decreases the favorability of β-hydride elimination to take place, the proposed main pathway for decomposition. The new catalyst containing this NHC ligand has shown increased activity and has achieved the highest TON yet. Our group has recently discovered vanadium oxo catalysts that are highly reactive towards unproductive olefin metathesis reactions, which we are exploring currently. My research focuses on the synthesis of V alkylidenes to improve catalysts' productivity for RCM and unproductive metathesis.

Synthesis of vanadium alkylidenes for productive and unproductive olefin metathesis

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