B(C6F5)3 Activation of Oxo Tungsten Complexes That Are Relevant to Olefin Metathesis

We have found that coordination of B(C6F5)(3) to an oxo ligand in tungsten oxo alkylidene bis(aryloxide) complexes, where the aryloxide is O-2,6-(mesityl)(2)C6H3 (HMTO) or 2,6-diadamantyl-4-methylphenoxide (dAdPO), accelerates the formation of metallacyclobutane complexes from alkylidenes as well as the rearrangement of metallacyclobutane complexes. In contrast, a tungstacyclopentane complex, W(O)(C4H8)(OHMT)(2), is relatively stable toward rearrangement in the presence of B(C6F5)(3). A careful balance of steric factors allows a single isomer of W(O)(trans-4,4-dimethylpent-2-ene)(dAdPO)(2) to be formed from W(O)(CH-t-Bu)(dAdPO)(2) in the presence of both ethylene and B(C6F5)(3).