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

Thermolysis of [TiMe₂{η⁵-C₅Me₄(CH₂CH₂CHCH₂)}₂] (1) in toluene at 120 °C for 4 h resulted in the formation of the cyclopentadiene ring-tethered titanacyclobutane [Ti^IV{η⁵-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-[TiCl₂{η⁵-C₅Me₄(CH₂)₇η⁵-C₅Me₄}] (3). Sunlight photolysis of 1 gave rise to the cyclopentadiene ring-tethered titanacyclopentane [Ti^IV{η⁵-C₅Me₄(CH₂CH₂CH(κ-CH)CH₂}₂] (5), the known product of cycloaddition reactions following the removal of chlorine atoms from [TiCl₂{η⁵-C₅Me₄(CH₂CH₂CHCH₂)}₂] with magnesium (as found by Horaček, M. Chem. Eur. J. 2000, 6, 2397).