Elimination and 1.1-insertion involving alkylidene ligands

Since transition metal carbene complexes serve as efficient catalysts for im- 

Transition metal alkyls having o -hydrogen(s) may undergo the a-hydrogen elimination process as shown in Eq. 7.25. 

The process is reversible and the hydrido-alkylidene species may not be observed when the a-alkyl species is thermodynamically more stable. However, when a route allowing the removal of the hydride, for example reductive elimination with another alkyl ligand as shown in Eq. 7.26, is provided, a stable alkylidene species can be isolated. 

The alkylidene complex, called Schrock type carbene complex, was first isolated in an attempt of synthesis of pentakis(neopentyl)tantalum(V) (Eq. 7.27) 

Further a-hydrogen elimination giving an alkylidyne complex was induced by addition of PMes to an alkylidene complex (Eq. 7.28). 

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