X-ray structure and electrophilic reactivity of a cationic, chiral tungsten(II) methylene complex

The structure of a tungsten(II) methylene complex, [Tp′(CO)(PhCCMe)WCH2][BAr′4] (2a), was obtained by taking advantage of the stabilizing, weakly coordinating counterion, BAr′4−, to form X-ray quality single crystals. The electrophilic reactivity of [Tp′(CO)(PhCCMe)WCH2][PF6] (2b) was surveyed with both neutral nucleophiles (triphenylphosphine and pyridine) and anionic nucleophiles (formed by deprotonation of phthalimide, diethyl malonate, t-butyl acetoacetate, and acetophenone) to give derivatives of the form [Tp′(CO)(PhCCMe)WCH2Nu]+,0. Crystal structures obtained for the phthalimide (5) and diethyl malonate (6) adducts are compatible with attack of the nucleophile from along the metal CO axis. The stereochemistry of the t-butyl acetoacetate adduct was determined by 2-D NOESY-NMR. Reaction of methylene carbene 2b with cyclohexene sulfide results in sulfur atom transfer to form a rare π-bound thioformaldehyde complex (9).