Experimental and Computational Studies of Dinitrogen Activation and Hydrogenation at a Tetranuclear Titanium Imide/Hydride Framework.

Author(s) Shima, T.; Luo, G.; Hu, S.; Luo, Y.; Hou, Z.
Journal J Am Chem Soc
Date Published 2019 Feb 13

The activation of N by a tetranuclear titanium(III) diimide/tetrahydride complex, [(Cp'Ti)(μ-NH)(μ-H)] (1) (Cp' = CMeSiMe), which was obtained by the reaction of the Cp'-ligated titanium trialkyl complex Cp'Ti(CHSiMe) with H and N, was investigated in detail by experimental and density functional theory studies. The reaction of 1 in the solid state with N (1 atm) at 180 °C gave the dinitride/diimide complex [(Cp'Ti)(μ-N)(μ-NH)] (2) through the incorporation, cleavage, and partial hydrogenation of one molecule of N and release of two molecules of H. At 130 °C, the formation of 2 was not observed, but instead, dehydrogenation of 1 took place through cleavage of the N-H bond in an imide ligand, followed by deprotonation of the other imide ligand with a hydride ligand, affording the dinitride/tetrahydride complex [(Cp'Ti)(μ-N)(μ-H)] (3). Upon heating under N (1 atm) at 180 °C, 3 was quantitatively converted to the dinitride/diimide complex 2. This transformation was initiated by migration of a hydride ligand to a nitride ligand to give one imide unit, followed by N coordination to a Ti atom and H release through the reductive elimination of two hydride ligands. The other imide ligand in 2 was formed by hydride migration to one of the two nitride ligands generated through the cleavage of the newly incorporated N unit. The hydrogenation of 2 with H (100 atm) at 180 °C afforded the tetraimide complex [(Cp'Ti)(μ-NH)] (4). This reaction was initiated by σ-bond metathesis between H and a titanium-nitride bond, followed by migration of the resulting hydride ligand to the remaining nitride ligand. In all of these transformations, the interplay among the hydride, imide, and nitride ligands, including the reversible dehydrogenation/hydrogenation of imide and nitride species, at the multimetallic titanium framework has a critically important role.

DOI 10.1021/jacs.8b13341
ISSN 1520-5126
Citation J Am Chem Soc. 2019;141(6):27132720.

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