Olefin Metathesis Catalysts Containing N,N′-Diamidocarbenes

A series of Ru-based olefin metathesis catalysts containing N,N′-diamidocarbenes (DACs) were synthesized and studied. X-ray crystallographic analysis revealed that the Ru−Ccarbene distances (1.938(5)−1.984(4) A) measured in the DAC-supported complexes were relatively short, particularly in comparison to the range of Ru−Ccarbene distances typically observed in analogous N-heterocyclic carbene (NHC) supported complexes (1.96−2.03 A). While the Tolman electronic parameters (TEP) of various DACs (2056−2057 cm−1) were calculated to be similar to that of PCy3 (2056 cm−1), the ring-closing metathesis (RCM) of diethyl diallylmalonate facilitated by DAC-supported Ru complexes proceeded at a relatively slow rate. However, unlike the phosphine-containing complexes, the DAC analogues catalyzed the RCM of diethyl dimethallylmalonate to its respective tetrasubstituted olefin. A series of electrochemical experiments revealed that the Ru complexes bearing a DAC ligand underwent oxidation at significantly higher potential...