Higman, C.S.; Rufh, S.A.; McDonald, R.; Fogg, D.E. “Synthesis and Dynamic Behavior of a Dimeric Ruthenium Benzylidene Complex Bearing a Truncated N-Heterocyclic Carbene Ligand” J. Organomet. Chem. 2017, Advance Article. DOI: 10.1016/j.jorganchem.2017.03.033
As the use of metathesis catalysts has become more prevalent in industry, understanding the decomposition pathway is crucial. The Fogg group at the University of Ottawa has been studying the decomposition ruthenium metathesis catalysts and have reported insights into the pathways for decomposition. One such pathway for decomposition can occur through the undesired C-H activation of the NHC ligand found on 2nd generation Grubbs catalysts. In this report, Fogg and co-workers use a “slimmed down” NHC ligand (IMe4) to suppress any C-H activation.
Treating 1st Generation Grubbs catalyst with the smaller NHC ligand, IMe4, resulted in a dimeric ruthenium species (Figure 1) with a surprisingly complex NMR spectra. Initial crystal structure elucidation showed the dimeric species to be ruthenium dimer (1), which was undergoing rapid rotation around the Ru=CHPh bond. These Ru=CHPh rotamers were the source of the complexity in the NMR spectrum. Furthermore, the catalyst was tested for metathesis activity and shown to be slow, but active in the presence of HCl or amberlyst.
Figure 1. Synthesis of ruthenium dimeric complex 1
As this report demonstrates there is still much to be discovered in the reactivity and formation of new ruthenium complexes. Undoubtedly as more variations of catalysts are synthesized doors to other applications may open.