Cross-Multicarrousel Mechanism and Kinetics of Mn-PNP Catalyzed Diamide Formation from the Dehydrogenation of Alcohols and Diamines.

Herein, a density functional theory based mechanistic and kinetics study of experimentally reported pincer metal complex catalyzed homogenous dehydrogenation of methanol and diamine into diamide is explored. The reaction proceeds through dehydrogenation and hydrogenation reactions for the reversible interconversion between methanol and diamine. The mechanism proceeds via a step-by-step formation of aldehyde, amide, and diamide complexes. The generated formaldehyde reacts with ethylenediamine in the second cycle to make monoamide, which reacts with formaldehyde from the first cycle to produce diamide. The complete diamide formation reaction follows a cross-multicarrousel type mechanism. The turnover-determining transition state is the formation of the first amide bond, where the addition of amine and metal aldehyde takes place. The alternative reaction of metal aldehyde and alcohol via an ester formation reaction is a minor path. The rate equation is derived from the most feasible path. From the dissociation dynamics simulations, the dehydrogenation reaction of metal hydride is found to be favorable, and a strong Mn and H2 interaction is present during the H2 release, which may facilitate the hydrogenation reaction. Diamide dissociation is more challenging than amide dissociation, and a high temperature is required for diamide dissociation dynamics.