From Alkyne and Cyclopropene Complexes

Alkynes react readily with a variety of transition metal complexes under thermal or photochemical conditions to form the corresponding 7t-complexes. With terminal alkynes the corresponding 7t-complexes can undergo thermal or chemically-induced isomerization to vinylidene complexes [128,130,132,133,547,556-569]. With mononuclear rj -alkyne complexes two possible mechanisms for the isomerization to carbene complexes have been considered, namely (a) oxidative insertion of the metal into the terminal C-Fl bond to yield a hydrido alkynyl eomplex, followed by 1,3-hydrogen shift from the metal to Cn [570,571], or (b) eoneerted formation of the M-C bond and 1,2-shift of H to Cp [572]. 

Vinylidene complexes are valuable intermediates for the preparation of heteroatom-substituted earbene eomplexes (Seetion 2.1.5) and other organometallic compounds, including non-heteroatom-substituted earbene eomplexes [573,574]. Examples of further transformations of vinylidene complexes include addition reac- 

Similar to alkynes, cyclopropenes also readily form transition metal 7i-complexes which can isomerize to carbene complexes thermally, photochemically, or che- 

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