4 years ago

Seleniranium Ions Undergo π-Ligand Exchange via an Associative Mechanism in the Gas Phase

Seleniranium Ions Undergo π-Ligand Exchange via an Associative Mechanism in the Gas Phase
Jonathan M. White, E.J. Bieske, Michael S. Scholz, Michael Rathjen, S. Fern Lim, Gabriel da Silva, Brian D. Adamson, Daniel Stares, George N. Khairallah, Neville J. A. Coughlan, Benjamin L. Harris, Richard A. J. O’Hair, Philippe Maître
Collision-induced dissociation mass spectrometry of the ammonium ions 4a and 4b results in the formation of the seleniranium ion 5, the structure and purity of which were verified using gas-phase infrared spectroscopy coupled to mass spectrometry and gas-phase ion-mobility measurements. Ion–molecule reactions between the ion 5 (m/z = 261) and cyclopentene, cyclohexene, cycloheptene, and cyclooctene resulted in the formation of the seleniranium ions 7 (m/z = 225), 6 (m/z = 239), 8 (m/z = 253), and 9 (m/z = 267), respectively. Further reaction of seleniranium 6 with cyclopentene resulted in further π-ligand exchange giving seleniranium ion 7, confirming that direct π-ligand exchange between seleniranium ion 5 and cycloalkenes occurs in the gas phase. Pseudo-first-order kinetics established relative reaction efficiencies for π-ligand exchange for cyclopentene, cyclohexene, cycloheptene. and cyclooctene as 0.20, 0.07, 0.43, and 4.32. respectively. DFT calculations at the M06/6-31+G(d) level of theory provide the following insights into the mechanism of the π-ligand exchange reactions; the cycloalkene forms a complex with the seleniranium ion 5 with binding energies of 57 and 62 kJ/mol for cyclopentene and cyclohexene, respectively, with transition states for π-ligand exchange having barriers of 17.8 and 19.3 kJ/mol for cyclopentene and cyclohexene, respectively.

Publisher URL: http://dx.doi.org/10.1021/acs.joc.7b00877

DOI: 10.1021/acs.joc.7b00877

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