BIS-(PI-PENTAMETHYLCYCLOPENTADIENYL) (2-M ETHYLIDENE) TITANACYCLOBUTANE - SELECTIVE INSERTION OF ISONITRILES AND DIPHENYLKETENE - FORMATIONOF 5-MEMBERED AND 6-MEMBERED METALLACYCLES

The reaction of isonitriles or diphenylketene with the titanacyclobuta ne derivative Cp(2)(star)TiC(=CH2)CH2CH2 (2) (Cp(star)=[C-5(CH3)(5)]) at room temperature afforded the five- and six-membered metallacycles Cp(2)(star)TiC(=CH2)CH2CH2C(=NR) (R = C6H11, 7a; C(CH3)(3), 7b) and Cp (2)(star)TiC(=CH2)CH2CH2C(=C(PH2)O (11), respectively, whose structure s have been characterized by spectral data and X-ray analysis. By usin g other cumulene type molecules instead of Ph(2)C=C=O, e.g. carbon dio xide or isocyanates, no insertion reaction is observed. Only monoinser tions in the Ti-C(sp)3 bond of 2 are found, without further subsequent reactions. The insertion of a second isonitrile or ketene molecule is prevented by the absence of a free coordination site on the metal com plexes 7 and 11. X-ray structure determination of 7a revealed that the heterocycle has an eta(1)-iminoacyl structure (Ti-N distance 3.080(3) Angstrom).