title: Platinum(II)-catalyzed cyclization sequence of aryl alkynes via C(sp3)-H activation: a DFT study.
abstract: The mechanism and intermediates of hydroalkylation of aryl alkynes via C(sp(3))-H activation through a platinum(II)-centered catalyst are investigated with density functional theory at the B3LYP/[6-31G(d) for H, O, C; 6-31+G(d,p) for F, Cl; SDD for Pt] level of theory. Solvent effects on reactions were explored using calculations that included a polarizable continuum model for the solvent (THF). Free energy diagrams for three suggested mechanisms were computed: (a) one that leads to formation of a Pt(II) vinyl carbenoid (Mechanism A), (b) another where the transition state implies a directed 1,4-hydrogen shift (Mechanism B), and (c) one with a Pt-aided 1,4-hydrogen migration (Mechanism C). Results suggest that the insertion reaction pathway of Mechanism A is reasonable. Through 4,5-hydrogen transfer, the Pt(II) vinyl carbenoid is formed. Thus, the stepwise insertion mechanism is favored while the electrocyclization mechanism is implausible. Electron-withdrawing/electron-donating groups substituted at the phenyl and benzyl sp(3) C atoms slightly change the thermodynamic properties of the first half of Mechanism A, but electronic effects cause a substantial shift in relative energies for the second half of Mechanism A. The rate-limiting step can be varied between the 4,5-hydrogen shift process and the 1,5-hydrogen shift step by altering electron-withdrawing/electron-donating groups on the benzyl C atom. Additionally, NBO and AIM analyses are applied to further investigate electronic structure changes during the mechanism.
authors: MOE Key Laboratory of Bioinorganic and Synthetic Chemistry/KLGHEI of Environment and Energy Chemistry, School of Chemistry and Chemical Engineering, Sun Yat-Sen University, Guangzhou 510275, People's Republic of China.
authors: Zhi-Feng
authors: ZF
authors: Li
authors: Yanzhong
authors: Y
authors: Fan
authors: Nathan J
authors: NJ
authors: DeYonker
authors: Xiting
authors: X
authors: Zhang
authors: Cheng-Yong
authors: CY
authors: Su
authors: Huiying
authors: H
authors: Xu
authors: Xianyan
authors: X
authors: Xu
authors: Cunyuan
authors: C
authors: Zhao
mesh_terms: D000478:Alkylation; D000480:Alkynes / Q000737:chemistry*; D002384:Catalysis; D003500:Cyclization; D007192:Indenes / Q000138:chemical synthesis* / Q000737:chemistry; D015394:Molecular Structure; D010984:Platinum / Q000737:chemistry*; D011789:Quantum Theory; D013816:Thermodynamics
chemical_list: D000480:Alkynes; D007192:Indenes; D010984:Platinum