We have previously reported that Ti-catalyzed multicomponent carboamination of alkynes with alkenes and azobenzene can yield either an a,b-unsaturated imine or cyclopropyl imine. These two different products share a common azatitanacyclehexene intermediate, and are proposed to be formed via either a b-H elimination or an a,g-coupling pathway, respectively. Herein, we report the synthesis of a model azatitanacyclohexene complex through the ring opening of a cyclopropyl imine with Cp2Ti(BTMSA) (BTMSA = bis(trimethylsilyl)acetylene). This complex readily undergoes thermal or reductant-catalyzed ring contraction to an azatitanacyclopentene, analogous to the formation of a,b-unsaturated imine in the catalytic reaction. We also observed that a cyclopropyl imine and an unsaturated imine were re-formed from the azatitanacyclohexene and azatitanacyclopentene, respectively, through azobenzene interchange. These transformations have been analyzed through Eyring analysis and substituent effect studies in order to understand thermodynamic and kinetic properties, such as activation enthalpy, entropy, KIE and rate order. Oxatitanacyles and oxazirconacycles analogues have also been synthesized and analyzed to compare their characteristics.

Cp2TiII mediated rearrangement of cyclopropylimines: Models for alkyne carboamination

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