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

作者：Mueller Carsten; Koch Rainer; Doye Sven

来源：Chemistry - A European Journal, 2008, 14(33): 10430-10436.

DOI：10.1002/chem.200801445

• alkenes
• amines
• hydroamination
• reaction mechanisms
• titanium

Three mechanistic pathways for the [Ind(2)TiMe(2)]-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-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-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-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 kJmol(-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.

• 出版日期2008