H–H and N–H Bond Cleavages of Dihydrogen and Ammonia by a Bifunctional Imido (NH)-Bridged Diiridium Complex: A DFT Study

The
mechanisms of H–H and N–H bond cleavages of dihydrogen
and ammonia mediated by the diiridium μ2-imido complex
[(Cp*Ir)2(μ2-H)­(μ2-NH)]+ (A; Cp* = η5-C5Me5) were theoretically investigated with the density functional
theory (DFT) method. Both oxidative addition and metal–ligand
cooperation modes have been studied for H–H and N–H
bond cleavages, respectively. The H–H bond cleavage most likely
occurs through competitive oxidative addition and metal–ligand
cooperation, and both cleavage modes have similar overall free energy
barriers (24.3 and 25.7 kcal/mol, respectively). The ligand-assisted
N–H bond heterolytic cleavage mechanism is proposed for the
NH3 reaction, and the general oxidative addition pathway
can be reasonably ruled out, as it is kinetically unfavorable.