Synthesis and Characterization of Cationic Tungsten(V) Methylidynes

Cationic tungsten(V) methylidynes [L4W(X)⋮CH]+[B(C6F5)4]- [L = PMe3, 0.5dmpe (dmpe = Me2PCH2CH2PMe2),
X = Cl, OSO2CF3] have been prepared in high yield by a one-electron oxidation of the neutral tungsten(IV)
methylidynes L4W(X)⋮CH with [Ph3C]+[B(C6F5)4]-. The ease and reversibility of the one-electron oxidation of
L4W(X)⋮CH were demonstrated by cyclic voltammetry in tetrahydrofuran (E1/2 ≈ −0.68 to −0.91 V vs Fc). The
paramagnetic d1 (S = 1/2) complexes were characterized in solution by electron spin resonance (g = 2.023−2.048,
quintets due to coupling to 31P) and NMR spectroscopy and Evans magnetic susceptibility measurements (μ =
2.0−2.1 μB). Single-crystal X-ray diffraction showed that the cationic methylidynes are structurally similar to the
neutral precursor methylidynes. In addition, the neutral (PMe3)4W(Cl)⋮CH was deprotonated with a strong base at
the trimethylphosphine ligand to afford (PMe3)3(Me2PCH2)W⋮CH, a tungsten(IV) methylidyne complex that features
a (dimethylphosphino)methyl ligand.