Group VI terminal carbyne complexes

Treatment of [Tp′(CO)₂W≡C-PPh ₃][PF₆] (Tp′ = hydridotris(3,5-dimethylpyrazolylborate) with Na[HBEt₃] in THF forms the methylidyne complex Tp′ (CO)₂W≡C-H via formyl and carbene intermediates Tp ′(CO)(C(O)H)W≡C-PPh₃ and Tp′(CO) ₂W=C(PPh₃)(H), respectively. Protonation of the Tp ′(CO)₂W≡C-H methylidyne complex with HBF ₄·Et₂O yields the cationic α-agostic methylidene complex, [Tp′(CO)₂W=CH₂][BF ₄]. The terminal carbide Tp′(CO)₂W≡C-Li adds electrophiles at the carbide carbon to generate Tp′(CO) ₂W≡C-R (R = CH₃, SiMe₃, I, C(OH)Ph ₂, CH(OH)Ph, and C(O)Ph) Fischer carbynes. Addition of excess Na[HBEt ₃] to neutral Tp′(CO)₂W≡C-H generates the anionic methylidene complex [Na][Tp′(CO)₂W=CH ₂]. Addition of PhSSPh to the anionic methylidene complex in solution generates the saturated tungsten product Tp′(CO) ₂W(η2-CH₂SPh) by net addition of the SPh + moiety. Phosphonium carbyne complexes of the type [Tp′ (CO)₂W≡CPMe₂Ph]+ add PhCH ₂MgCl and C₃H₅MgCl at C_α to generate Tp′(CO)₂W=C(CH₂R)(PMe₂Ph) zwitterionic carbenes as reactive intermediates which lose PMe₂Ph to form neutral Tp′(CO)₂W≡CCH₂ R (R = Ph, C₂H₃) complexes. Deprotonation of these alkyl carbyne complexes with strong base occurs at C_β to form vinylidene anions [Tp′(CO)₂W=C=C(H)(R)] −. Phenylvinylidene anion [Tp′(CO) ₂W=C=C(H)(Ph)]− has multiple resonance contributors, but electrophilic additions occur exclusively at C_β. Addition of n-BuLi to chiral carbyne derivative Tp′(CO)₂ W≡CC(H)(CH₃)(Ph) generates a methyl substituted phenylvinylidene anion which also adds Me+ at C_β to form Tp ′(CO)₂W≡C(CH₃)₂Ph. Vinylvinylidene anion [Tp′(CO)₂W=CCHCH=CH₂] − adds MeI at C_β to generate Tp′ (CO)₂W≡CC(CH₃)(H)CH=CH₂). Treatment of methylvinylcarbyne with n-BuLi generates the anion [Tp′(CO) ₂W=C=C(CH₃)CH=CH₂]−,$$ which adds MeI primarily at C_β to form Tp′ (CO)₂W≡CC(CH₃)₂CH=CH₂ ; some methylation at C_δ to generate Tp′ (CO)₂W≡CC(CH₃)=C(H)(CH₂CH ₃) is observed. Isomerization of the allyl carbyne complex to a 4:1 mixture of E:Z vinyl carbyne Tp′(CO) ₂W≡CC(H)=C(H)(CH₃) isomers was achieved through base catalyzed conversion by NEt₃ and protonation of the vinylvinylidene using water as the H+ source. Deprotonation of Tp′ (CO)₂W≡CCH₂CH=CHC=W(CO)₂Tp ′ with strong base forms the symmetric [Tp...