Stability of Second Generation Grubbs' Alkylidenes to Primary Amines: Formation of Novel Ruthenium-Amine Complexes

The stability of second generation Grubbs’ alkylidenes to primary amines relative to the first generation derivatives is investigated. For both Grubbs’ alkylidene derivatives, the tricyclohexylphosphine (PCy3) ligand is displaced by n‐butylamine and diethylenetriamine. However, while displacement of PCy3 in first generation Grubbs’ alkylidene derivatives results in decomposition of the catalyst, the N‐heterocyclic carbene (NHC) ligand in second generation derivatives is not displaced by primary amines present in up to 100 equivalents. The result is the formation of new stable ruthenium‐amine complexes. These complexes are characterized and their catalytic activity is evaluated in ring‐closing metathesis (RCM) and ring‐opening metathesis (ROMP) reactions. While the amine complexes evaluated were minimally active in RCM reactions, the ruthenium‐butylamine complex was significantly active in ROMP and exhibited an initiation rate constant that was at least an order of magnitude greater than that of the second generation Grubbs’ alkylidene from which it was synthesized.