N–H Activation of Ammonia by [{M(μ-OMe)(cod)}<sub>2</sub>] (M = Ir, Rh) Complexes: A DFT Study

In this work, a computational study at the DFT level is carried out to determine the reaction mechanism for the N–H bond activation of ammonia by dinuclear [{M­(μ-OMe)­(cod)}<sub>2</sub>] complexes (M = Ir, Rh) to yield amido species [{M­(μ-NH<sub>2</sub>)­(cod)}<sub>2</sub>] reported experimentally by Mena et al. (<i>Angew. Chem., Int. Ed.</i> <b>2011</b>, <i>50</i>, 11735–11738). A stepwise mechanism is proposed for the replacement of μ-OMe bridging ligands considering associative or dissociative approaches for NH<sub>3</sub> coordination to the metal. Reaction pathways for the homolytic and heterolytic N–H σ-bond cleavage of ammonia, such as oxidative addition through M<sup>III</sup> species or hydrogen transfer to the ligand, are investigated. The energetically preferred mechanism involves the participation of both metallic centers through the formation of and intermediate bearing M<sub>1</sub>-NH<sub>3</sub> and M<sub>2</sub>-OMe moieties followed by heterolytic hydrogen transfer of the amino ligand to the methoxo ligand. A bonding analysis on the metallacycle [M<sub>2</sub>X<sub>2</sub>] core (M = Ir, Rh; X = μ-OMe, μ-NH<sub>2</sub>) is performed, showing that the amido bridging complex is stabilized due to the presence of metal–metal bonding interactions.