Phosphoranes, alkylidene transfer

The most common method for the generation of the metal alkylidene species seems to be a-elimination from an intermediate dialkyl-metal species. This procedure gives the most active catalysts. Above we mentioned the addition of other carbene precursors, which leads to active catalysts. Other methods to generate the metal alkylidene species involve alkylidene transfer from phosphoranes [16] or ring-opening of cyclopropenes [17], In Chapter 16.4 we will describe a few compounds that are active by themselves as metathesis catalysts. 

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.

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

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