Ethene Elimination during Thermolysis of Bis(3-butenyltetramethylcyclopentadienyl)dimethyltitanium

Thermolysis of [TiMe25-C5Me4(CH2CH2CHCH2)}2] (1) in toluene at 120 °C for 4 h resulted in the formation of the cyclopentadiene ring-tethered titanacyclobutane [TiIV5-C5Me4CH2CH2CH(κ-CH)}2CH2] (2) in virtually quantitative yields. Thermolysis in an NMR tube at 100 °C revealed that initial elimination of methane is followed by addition of one 3-butenyl double bond to a titanocene−methylidene moiety. The formed titanacyclobutane intermediate [Ti{η5-C5Me4(CH2CH2CHCH2)}{η5-C5Me4CH2CH2CH(κ-CH)CH2CH2(κ-CH2)}] (4) then underwent a metathesis reaction with the pendant 3-butenyl to give 2 and free ethene. Cleavage of Ti−C bonds of 2 with HCl afforded stable ansa-[TiCl25-C5Me4(CH2)7η5-C5Me4}] (3). Sunlight photolysis of 1 gave rise to the cyclopentadiene ring-tethered titanacyclopentane [TiIV5-C5Me4(CH2CH2CH(κ-CH)CH2}2] (5), the known product of cycloaddition reactions following the removal of chlorine atoms from [TiCl25-C5Me4(CH2CH2CHCH2)}2] with magnesium (as found by Horaček, M. Chem. Eur. J. 2000, 6, 2397).