B(C<sub>6</sub>F<sub>5</sub>)<sub>3</sub> Co-Catalyst\nPromotes Unconventional Halide Abstraction from Grubbs I to Enhance\nReactivity and Limit Decomposition

Ruthenium based Grubbs metathesis has become a commonplace\nreaction\nfor synthetic chemists. Development of new generations of catalysts\nevolving from Grubbs I (GI) have led to greater stability, functional\ngroup compatibility, and superior reactivities. However, these advancements\nlead to increased costs. To this end, we report here how the addition\nof the commercially available tris(pentafluorophenyl)borane Lewis\nacid, which has become a common place catalyst in its own right, leads\nto enhanced reactivity of GI. Moreover, the increased reactivity arises\nvia halide abstraction rather than traditional phosphine dissociation,\nproviding ring-opening metathesis polymerization products that are\ndivergent from those synthesized without the Lewis acid cocatalyst.