Temperature Dependence of the Ring Opening of Cyclopropene Imines on Thorium Metallocenes.

The reactions of two highly strained cyclopropenimine ligands and ( = -tetraisopropyl-3-iminocycloprop-1-ene-1,2-diamine, = -tetracyclohexyl-3-iminocycloprop-1-ene-1,2-diamine) with three thorium precursors CpThCl, CpTh(Cl)(CH), and CpTh(CH) were studied. At -20 °C, and react with CpThCl to form ( = CpThCl(L1H)) and ( = CpThCl(L2H)), respectively, where the neutral ligand coordinates to the thorium metal center. Coordination of the ligand to the thorium metal center introduces aromaticity at the cyclopropene ring of the ligand. Reaction at room temperature results in the ring opening of the ligand to form ( = CpThCl(()-2,3-bis(diisopropylamino)acrylonitrile) and ( = CpThCl(()-2,3-bis(dicyclohexylamino)acrylonitrile), where the cyclopropenimine converts into a nitrile and coordinates to the thorium metal center. Reaction of and with CpTh(Cl)(CH) and/or CpTh(CH) at -20 °C results in a rapid methanolysis reaction and forms CpTh(L1/L2)(CH/Cl)-type complexes ( = CpTh(L1)(CH)), ( = CpTh(L2)(CH), ( = CpTh(L1)(Cl), and ( = CpTh(L2)(Cl). On the other hand, at room temperature, these reactions result in a ring opening of the ligand. Room-temperature reaction of and with CpTh(CH) results in ( = CpTh(CH)(()-3-imino--tetraisopropylbut-1-ene-1,2-diamine) and ( = CpTh(CH)(()-3-imino--tetracyclohexylbut-1-ene-1,2-diamine). Similarly, at room temperature, and react with CpTh(Cl)(CH) to form ( = CpTh(Cl)(()-3-imino- -tetraisopropylbut-1-ene-1,2-diamine) and ( = Cp*Th(Cl)(()-3-imino--tetracyclohexylbut-1-ene-1,2-diamine). The ring-opening reaction is assisted by the nucleophilic attack of the thorium-coordinated methyl group to the highly strained cyclopropene imine carbon.