Get access

Mechanism of the Intramolecular Hydroamination of Alkenes Catalyzed by Neutral Indenyltitanium Complexes: A DFT Study



Three mechanistic pathways for the [Ind2TiMe2]-catalyzed intramolecular hydroamination of alkenes have been investigated by employing density functional theory calculations on the possible intermediates and transition states. The results indicate that the reaction cycle proceeds via a Ti–imido–amido complex as the catalytically active species. However, at the moment, the question as to whether this imido–amido complex is involved in a [2+2]-cycloaddition with the alkene or a newly proposed insertion of the alkene into a Ti[BOND]N single bond cannot be answered; the calculated barriers of both the insertion mechanism and the [2+2]-cycloaddition mechanism are similar (143 vs. 136 kJ mol−1), and both pathways are in accordance with the experimentally observed rate law (first-order dependence on the aminoalkene concentration). Interestingly, the newly proposed insertion mechanism that takes place by an insertion of the alkene moiety into the Ti[BOND]N single bond of an imido–amido complex seems to be much more likely than a mechanism that involves an alkene insertion into a Ti[BOND]N single bond of a corresponding trisamide. The latter mechanism, which has been proposed in analogy to rare-earth-metal-catalyzed hydroamination reactions, can be ruled out for two reasons: a surprisingly high activation barrier (164 kJ mol−1) and the fact that the rate-limiting insertion step is independent of the aminoalkene concentration. This is in sharp contrast to the experimental findings for indenyltitanium catalysts.

Get access to the full text of this article