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

Abstract

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.