Molybdenum and Tungsten Alkylidene Complexes That Contain a 2‑Pyridyl-Substituted Phenoxide Ligand

In the interest of preparing molybdenum and tungsten alkylidene complexes for olefin metathesis that are longer-lived at high temperatures (∼150 °C or above), we synthesized complexes that contain a phenoxide ligand with a 2-pyridyl in one ortho position and a mesityl (Mes) or 2,4,6-i-Pr3­C6H2 (Trip) in the other ortho position ([Mes­ON]− or [Trip­ON]−, respectively). The alkylidene (neophylidene) complexes that were prepared include W­(O)­(CHC­Me2Ph)­(Me2­Pyr)­(RON) (R = Mes or Trip), Mo­(NC6F5)­(CHC­Me2Ph)­(RON)­Cl, Mo­(N-2,6-Me2­C6H3)­(CHC­Me2Ph)­(RON)­Cl, Mo­(N-t-Bu)­(CHC­Me2Ph)­(RON)­Cl, and M­(N-2,6-i-Pr2­C6H3)­(CHC­Me2Ph)­(TripON)­(OTf) (M = Mo or W). The reaction between Mo­(NAr)­(CHC­Me2Ph)­(TripON)­(OTf) and ethylene yielded an ethylene complex, Mo­(NAr)­(C2H4)­(TripON)­(OTf)­(ether). All neophylidene complexes were essentially unreactive toward terminal olefins at 22 °C and showed modest homocoupling activity (at 80 or 100 °C) and alkane metathesis activity (at 150 and 200 °C). W­(O)­(CHC­Me2Ph)­(Me2Pyr)­(MesON) also stereoselectively polymerized several substituted norbornadienes at 100 °C.