Anorganische Chemie - Beckhaus

Methylidenetitanacyclobutane vs. Titanocene-Vinylidene - Versatile Building Blocks

D. Enders, H.-J. Gais, W. Keim (Hrsg.), Vieweg Verlag, Braunschweig 1993, 131 - 149
Organic Synthesis via Organometallics (OSM 4), Proceedings of the Fourth Symposium in Aachen, July 15th to 18th, 1992,

R. Beckhaus

The reaction of vinyllithium with Cp*2TiCl2 (Cp* = [C5(CH3)5]) in a molar ratio of 2:1 quantitatively yields the unexpected titanacyclobutane derivative Cp*2TiC(=CH2)CH2CH2 2. The isolated complex 2 has been characterized by spectroscopic methods and by X-ray structure determination. The chemical reactivity of 2 is characterized by the splitting of the four membered ring at higher temperatures, forming a titanocene fragment {Cp*2Ti=C=CH2} (6) and ethylene. This cycloreversion is confirmed by the fragmentation behavior in the mass spectrometer, and some aspects of it have been studied by Extended Hckel Model calculation. The system titanacyclobutane 2 and titanocenevinylidene 6 can be used in a large scale of different organometallic reactions. So 2 exhibits typical properties of an alkyl complex and undergoes insertion reactions with isonitriles or ketenes, forming 5- and 6-membered metallacycles. On the other hand cycloreversion products can be prepared due to the typical vinylidene character of 6. By reaction of 6 with metal carbonyls, followed by a vinylidene-acetylene rearrangement, 5-membered cyclic FISCHER-Carbene complexes can be isolated in high yield.