Platinum(II)-Catalyzed Cyclization Sequence of Aryl Alkynes via C(sp3)?H Activation: A DFT Study

摘要

The mechanism and intermediates of hydroalkylation of aryl alkynesnvia C(sp3)−H activation through a platinum(II)-centered catalyst are investigatednwith density functional theory at the B3LYP/[6-31G(d) for H, O, C; 6-31+G(d,p)nfor F, Cl; SDD for Pt] level of theory. Solvent effects on reactions were explorednusing calculations that included a polarizable continuum model for the solventn(THF). Free energy diagrams for three suggested mechanisms were computed: (a)none that leads to formation of a Pt(II) vinyl carbenoid (Mechanism A), (b) anothernwhere the transition state implies a directed 1,4-hydrogen shift (Mechanism B), andn(c) one with a Pt-aided 1,4-hydrogen migration (Mechanism C). Results suggest thatnthe insertion reaction pathway of Mechanism A is reasonable. Through 4,5-hydrogenntransfer, the Pt(II) vinyl carbenoid is formed. Thus, the stepwise insertionnmechanism is favored while the electrocyclization mechanism is implausible.nElectron-withdrawing/electron-donating groups substituted at the phenyl and benzylnsp3 C atoms slightly change the thermodynamic properties of the first half of Mechanism A, but electronic effects cause ansubstantial shift in relative energies for the second half of Mechanism A. The rate-limiting step can be varied between the 4,5-nhydrogen shift process and the 1,5-hydrogen shift step by altering electron-withdrawing/electron-donating groups on the benzylnC atom. Additionally, NBO and AIM analyses are applied to further investigate electronic structure changes during thenmechanism.