Alkylidene complexes phosphoranes

Thermolysis of ()) -cyclopentadienyl)bis(neopentyl)(tri-methylphosphine)vanadium(I) (82) in the presence of 1,2-bis(dimethylphosphuio)ethane leads to the formation of the Schrock-type see Schrock-type Carbene Complexes) alkylidene vanadium complex (83), which is supported by X-ray crystallographic analysis (Scheme 45). " The imido vanadium complex (84) is converted to the corresponding alkylidene complex (86) on treatment with ben-zylidene(triphenyl)phosphorane (85) via substitution of the phosphine ligand (Scheme 46). ... 

Another attractive route to the synthesis of highly reactive tungsten carbene complexes involves alkylidene transfer from phosphoranes. Arylimido tungsten... 

Scheme 5.3 Synthesis of a tungsten alkoxyimidoalkylidene complex by alkylidene transfer from a phosphorane to a tungsten imide.

Some systems behave in a way compatible with (I) and have been included in this chapter. In contrast, the Wittig reaction of stable alkyliden-phosphoranes with carbonylic compounds has been shown to conform to a more complex mechanism , of the following type... 

Scheme 3. Sjmthesis of a Tungsten Alkoxyimidozilkylidene Complex by Alkylidene Transfer from a Phosphorane to a Tungsten Imide...

---