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.