98268-71-4Relevant academic research and scientific papers
Preparation of di-tert-butoxytungsten(VI) alkylidene complexes by protonation of tri-tert-butoxytungsten(VI) alkylidene complexes
Freudenberger, John H.,Schrock, Richard R.
, p. 1937 - 1944 (2008/10/08)
W(CCMe3)(OCMe3)3 reacts with 2 equiv of HX (X = Cl, Br, MeCO2, PhCO2, OPh, OC6F5, O-p-C6H4Cl) to give trigonal-bipyramidal neopentylidene complexes of the type W(CHCMe3)(OCMe3)2X2. Octahedral complexes of the type W(CHCMe3)(OCMe3)2X2(py) (X = Cl, Br, I, O2CCF3) in general are more stable than five-coordinate species. A six-coordinate propylidene complex, W(CHEt)(OCMe3)2Cl2(py), can be prepared but analogous five-coordinate species, W(CHEt)(OCMe3)2X2 (X = phenoxide, Cl, Br), evidently are too unstable to isolate. Addition of carboxylic acids to W(CEt)(OCMe3)3 yields unstable complexes of the type W(CHEt)(OCMe3)2(O2CR′)2 that rearrange to propylene complexes W(propylene)(OCMe3)2-(O2CR′)2 in a reaction that is second order in W. The rearrangement is relatively fast when catalyzed by added R′CO2H. It is proposed that the α-carbon atom of the alkylidene ligand is protonated to give an alkyl ligand which subsequently loses a proton from the β-carbon atom to give the olefin. Addition of only 1 equiv of R′CO2H to W(CR″)(OCMe3)3 (R″ = Me, Et) yields relatively stable alkylidene complexes of the type W(CHR″)(OCMe3)3(O2CR′).
