Tantalum alkylidene complexes arise by treating trialkyltantalum dichloride with alkyl lithium reagents.  This reaction initially forms a thermally unstable tetraalkyl-monochloro-tantalum complex, which undergoes α-hydrogen elimination, followed by alkylation of the remaining chloride.               
Tantalum alkylidene complexes are nucleophilic. They effect a number of reactions including: olefinations, olefin metathesis, hydroaminoalkylation of olefins, and conjugate allylation of enones.  
Ethylene, propylene, and styrene react with tantalum alkylidene complexes to yield olefin metathesis products.