Reactions of an amphoteric terminal tungsten methylidyne complex

Treatment of [Tp ' (CO)(2)W equivalent toC-PPh3] [PF6] (Tp ' = hydridotris(3,5-dimethylpyrazolylborate)) with Na[HBEt3] in THF forms the methylidyne complex Tp ' (CO)(2)W equivalent toC-H via formyl and carbene intermediates Tp ' (CO)(C(O)H)W equivalent toC-PPh3 and Tp ' (CO)(2)W=C(PPh3)(H), respectively. Spectroscopic features reported for Tp ' (CO)(2)W equivalent toC-H include the W equivalent toC stretch (observed by both IR and Raman spectroscopy) and the W-183 NMR signal (detected by a H-1, W-183 2D HMQC experiment). Protonation of the Tp ' (CO)(2)W equivalent toC-H methylidyne complex with HBF4. Et2O yields the cationic alpha -agostic methylidene complex [Tp ' (CO)(2)W=CH2] [BF4]. The methylidyne complex Tp ' (CO)(2)W equivalent toC-H can be deprotonated with alkyllithium reagents to provide the anionic terminal carbide Tp ' (CO)(2)W equivalent toC-Li; a downfield resonance at 556 ppm in the C-13 NMR spectrum has been assigned to the carbide carbon. The terminal carbide Tp ' (CO)(2)W equivalent toC-Li adds electrophiles at the carbide carbon to generate Tp ' (CO)(2)W equivalent toC-R (R = CH3, SiMe3, I, C(OH)Ph-2, CH(OH)Ph, and C(O)Ph) Fischer carbynes. A pK(a) of 28.7 was determined for Tp ' (CO)(2)W equivalent toC-H in THF by titrating the terminal carbide Tp ' (CO)(2)W equivalent toC-Li with a-benzylpyridine and monitoring its conversion to Tp ' (CO)(2)W equivalent toC-H with in situ IR spectroscopy. Addition of excess Na[HBEt3] to neutral Tp ' (CO)(2)W equivalent toC-H generates the anionic methylidene complex [Na][Tp ' (CO)(2)W=CH2], The synthetic methodology for generating an anionic methylidene complex by hydride addition to neutral Tp ' (CO)(2)W equivalent toC-H contrasts with routes that utilize a-hydrogen abstraction or hydride removal from neutral methyl precursors to generate methylidene complexes. Addition of PhSSPh to the anionic methylidene complex in solution generates the saturated tungsten product Tp ' (CO)(2)W(eta (2)-CH2-SPh) by net addition of the SPh+ moiety.