Reactivity of Acetylenes toward the Titanocene Vinylidene Fragment [Cp*2Ti=C=CH2]. Formation of Methylenetitanacyclobutenes and Vinyltitanium Acetylides. Crystal and Molecular Structures of Cp*2TiCR'=CR''C=CH2 (R ' = R'' = CH3; R' = SiMe3, R'' = C6H5) and

R. Beckhaus , J. Sang, T. Wagner, B. Ganter 
Organometallics 1996, 15, 1176-1187

The titanocenevinylidene intermediate [Cp*2Ti=C=CH2] reacts with symmetrical and unsymmetrical alkynes, giving methylenemetallacyclobutenes Cp*2Ti-CR=CR-C=CH2. When using unsymmetrical alkynes, different regioisomers can be isolated. With acidic acetylenes, vinyltitaniumacetylides are formed. X-ray structures and reactivities of both complex types are discusssed. The regioselectivity of the formation of methylenetitanacyclobutenes when using unsymmetrically substituted acetylenes is attributed to the polarity of the CC-bond, based on 13C-NMR data. Selective insertion reactions with isonitriles are observed.

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