Ligand-Controlled CO2 Activation Mediated by Cationic Titanium Hydride Complexes, [LTiH](+) (L=Cp-2, O)

摘要

CO2 activation mediated by [LTiH](+) (L=Cp-2, O) is observed in the gas phase at room temperature using electrospray-ionization mass spectrometry, and reaction details are derived from traveling wave ion-mobility mass spectrometry. Wheresas oxygen-atom transfer prevails in the reaction of the oxide complex [OTiH](+) with CO2, generating [OTi(OH)](+) under the elimination of CO, insertion of CO2 into the metal-hydrogen bond of the cyclopentadienyl complex, [Cp2TiH](+), gives rise to the formate complex [Cp2Ti(O2CH)](+). DFT-based methods were employed to understand how the ligand controls the observed variation in reactivity toward CO2. Insertion of CO2 into the TiH bond constitutes the initial step for the reaction of both [Cp2TiH](+) and [OTiH](+), thus generating formate complexes as intermediates. In contrast to [Cp2Ti(O2CH)](+) which is kinetically stable, facile decarbonylation of [OTi(O2CH)](+) results in the hydroxo complex [OTi(OH)](+). The longer lifetime of [Cp2Ti(O2CH)](+) allows for secondary reactions with background water, as a result of which, [Cp2Ti(OH)](+) is formed. Further, computational studies reveal a good linear correlation between the hydride affinity of [LTi](2+) and the barrier for CO2 insertion into various [LTiH](+) complexes. Understanding the intrinsic ligand effects may provide insight into the selective activation of CO2.