DFT Investigation of a Nonclassical Oxidative Addition-Reductive Elimination Pathway in the Pd(0)/Pd(II)/Pd(0) Cycle...

Density functional theory calculations were conducted to investigate the Pd-catalyzed dual hydroamination of cycloheptatriene leading to tropene formation. The results reveal a nonclassical oxidative addition-reductive elimination mechanism operating within the Pd(0)/Pd(II)/Pd(0) catalytic cycle. In this mechanism, the Pd(0) to Pd(II) transformation occurs via an outer-sphere protonation-oxidation process, while the reverse Pd(II) to Pd(0) transformation proceeds through nucleophilic attack-induced reductive coupling. The major product, tropene, is formed through the energetically favorable outer-sphere protonation-oxidation pathway, whereas the byproduct, 1,2-dihydroquinoline, arises from a less favorable inner-sphere pathway, with an energy difference of 3.1 kcal/mol. This energy aligns well with the experimentally observed product ratio of 80:12. Moreover, the formation of the η³-allyl-Pd(II) intermediate is identified as the rate-determining step, with an associated energy barrier of 18.8 kcal/mol. These findings provide mechanistic insights into Pd-catalyzed hydroamination and offer guidance for the design of more selective catalytic systems.