A Transition-Metal−η⁴-Diene Cation Can Undergo Nucleophilic Addition at the Internal Carbon

Treatment of CpW(CO)₂(η⁴-cyclohexadiene)BF₄ with RMgBr (R = methylvinyl, phenyl, naphthyl) in cold THF (−78 °C) afforded the CpW(CO)₂[(1,2,4-η)-1-CO-2-R-cyclohexene] complex as the major product; this result provides an example of a nucleophile attacking the internal carbon of a cationic η⁴-diene fragment.