Deprotonation of Cationic Tungsten(IV) Aqua−Oxo−Alkyne Complexes To Form Dioxo−Vinyl Tungsten(VI) Complexes

Chiral tungsten(IV) aqua−oxo−alkyne complexes, [Tp‘W(O)(H2O)(RC⋮CR)][OTf] (R = H (1); R = Me (2));
(Tp‘ = hydridotris(3,5-dimethylpyrazolyl)borate; OTf = trifluoromethanesulfonate), have been prepared by halide
abstraction from iodide precursors. These cationic complexes have been characterized with triflate as the
counteranion. The tautomeric dihydroxo isomer has not been observed. The neutral triflate adduct Tp‘W(O)(OTf)(HC⋮CH) (3) has also been isolated. Cationic complexes 1 and 2 undergo deprotonation and isomerization
when exposed to Al2O3 to give the dioxo−vinyl compounds Tp‘W(O)2(CHCH2) (6) and Tp‘W(O)2[C(Me)C(H)(Me)] (7), reflecting the conversion of the WIV(OH)(RC⋮CR) fragment to WVI(O)(RCCHR). The
presumed intermediates, neutral oxo−hydroxo compounds Tp‘W(O)(OH)(RC⋮CR) (R = H (9); R = Me (10)),
can be accessed by deprotonation of 1 or 2 with NaOH. Conversion of 9 to 6 was achieved thermally upon
heating at 100 °C for 2 days. X-ray structural data have provided solid-state structures of both the cationic aqua
complex 2 and the dioxo−vinyl complex 6.