Fast "Wittig-Like" Reactions As a Consequence of the Inorganic Enamine Effect.

The tungsten alkylidyne [CF3-ONO]W ≡CC(CH3)3(THF)2 (3) {where CF3-ONO = (MeC6H3[C- (CF3)2O] )2N3-} supported by a trianionic pincer-type ligand demonstrates enhanced nucleophilicity in unusually fast "Wittig-like" reactions. Experiments are designed to provide support for an inorganic enamine effect that is the origin of the enhanced nucleophilicity. Treating complex 3 with various carbonyl-containing substrates provides tungsten-oxo-vinyl complexes upon oxygen atom transfer. The rates of reactivity of 3 are compared with the known alkylidyne (DIPP)3W ≡CC(CH3)3 (DIPP = 2,6-diisopropylphenoxide). In all cases (except acetone), complex 3 exhibits significantly faster overall rates than (DIPP)3W ≡ CC(CH3)3. New oxo-vinyl complexes are characterized by NMR, combustion analysis and single crystal X-ray diffraction. Treating 3 with acid chlorides provides the tungsten oxo chloride species [CF3-ONO]W(0)Cl (4) and disubstituted alkynes. In the case of acetone the oxo-vinyl complex results in two rotational isomers 10syn and 10anti( The rate of isomerization was determined for the forward and reverse directions and was complimented with DFT calculations. [ABSTRACT FROM AUTHOR]