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.