SURPRISING DIFFERENCES IN THE CYCLOADDITION REACTIONS OF CUMULENES AND HETEROCUMULENES TO VINYLIDENETITANOCENE - FORMATION OF 4-MEMBERED OR 5-MEMBERED TITANACYCLES

Liberation of ethylene from titaniumcyclobutane 1 generates the corresponding metallaallene, Cp2*Ti = C = CH2, which surprisingly behaves differently in trapping reactions with various compounds. In the presence of carbon dioxide, ketenes, and isocyanates the four-membered titanacycles 2 (X = 0, CR2, and NR, respectively) form, whereas with metal carbonyls [L(n)MCO] the products are the Fischer carbene complexes 3, which have a planar metallacyclopentene unit. Cp* = eta5-C5Me5.(~)[GRAPHICS]