Gas-phase ion-molecule reactions of copper hydride anions [CuH2]- and [Cu2H3]-
Zavras, A and Ghari, H and Ariafard, A and Canty, AJ and O'Hair, RAJ, Gas-phase ion-molecule reactions of copper hydride anions [CuH2]- and [Cu2H3]-, Inorganic Chemistry, 56, (5) pp. 2387-2399. ISSN 0020-1669 (2017) [Refereed Article]
Gas-phase reactivity of the copper hydride anions [CuH2]– and [Cu2H3]– toward a range of neutral reagents has been examined via multistage mass spectrometry experiments in a linear ion trap mass spectrometer in conjunction with isotope labeling studies and Density Functional Theory (DFT) calculations. [CuH2]– is more reactive than [Cu2H3]–, consistent with DFT calculations, which show it has a higher energy HOMO. Experimentally, [CuH2]– was found to react with CS2 via hydride transfer to give thioformate (HCS2–) in competition with the formation of the organometallic [CuCS2]– ion via liberation of hydrogen; CO2 via insertion to produce [HCuO2CH]–; methyl iodide and allyl iodide to give I– and [CuHI]–; and 2,2,2-trifluoroethanol and 1-butanethiol via protonation to give hydrogen and the product anions [CuH(OCH2CF3)]− and [CuH(SBu)]−. In contrast, the weaker acid methanol was found to be unreactive. DFT calculations reveal that the differences in reactivity between CS2 and CO2 are due to the lower lying π* orbital of the former, which allows it to accept electron density from the Cu center to form the initial three-membered ring complex intermediate, [H2Cu(η2-CS2)]−. In contrast, CO2 undergoes the barrierless side-on hydride transfer promoted by the high electronegativity of the oxygen atoms. Side-on SN2 mechanisms for reactions of [CuH2]– with methyl iodide and allyl iodide are favored on the basis of DFT calculations. Finally, the DFT calculated barriers for protonation of [CuH2]– by methanol, 2,2,2-trifluoroethanol, and 1-butanethiol correlate with their gas-phase acidities, suggesting that reactivity is mainly controlled by the acidity of the substrate.
gas-phase ion-molecule reactions, copper, density functional theory (DFT)