Zavras Athanasios, Ghari Hossein, Ariafard Alireza, Canty Allan J, O'Hair Richard A J
School of Chemistry and Bio21 Molecular Science and Biotechnology Institute, University of Melbourne , 30 Flemington Road, Parkville, Victoria 3010, Australia.
Department of Chemistry, Faculty of Science, Central Tehran Branch, Islamic Azad University , Shahrak Gharb, Tehran, Iran.
Inorg Chem. 2017 Mar 6;56(5):2387-2399. doi: 10.1021/acs.inorgchem.6b02145. Epub 2017 Feb 10.
Gas-phase reactivity of the copper hydride anions [CuH] and [CuH] 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. [CuH] is more reactive than [CuH], consistent with DFT calculations, which show it has a higher energy HOMO. Experimentally, [CuH] was found to react with CS via hydride transfer to give thioformate (HCS) in competition with the formation of the organometallic [CuCS] ion via liberation of hydrogen; CO via insertion to produce [HCuOCH]; 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(OCHCF)] and [CuH(SBu)]. In contrast, the weaker acid methanol was found to be unreactive. DFT calculations reveal that the differences in reactivity between CS and CO 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, [HCu(η-CS)]. In contrast, CO undergoes the barrierless side-on hydride transfer promoted by the high electronegativity of the oxygen atoms. Side-on S2 mechanisms for reactions of [CuH] with methyl iodide and allyl iodide are favored on the basis of DFT calculations. Finally, the DFT calculated barriers for protonation of [CuH] 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.
通过线性离子阱质谱仪中的多级质谱实验，结合同位素标记研究和密度泛函理论（DFT）计算，研究了氢化铜阴离子[CuH]和[CuH]对一系列中性试剂的气相反应活性。[CuH]比[CuH]更具反应活性，这与DFT计算结果一致，DFT计算表明其具有更高能量的最高占据分子轨道（HOMO）。实验发现，[CuH]与CS通过氢化物转移反应生成硫代甲酸酯（HCS），同时与通过释放氢形成有机金属[CuCS]离子相互竞争；与CO通过插入反应生成[HCuOCH]；与碘甲烷和烯丙基碘反应生成I和[CuHI]；与2,2,2-三氟乙醇和1-丁硫醇通过质子化反应生成氢和产物阴离子[CuH(OCHCF)]和[CuH(SBu)]。相比之下，发现酸性较弱的甲醇没有反应活性。DFT计算表明，CS和CO反应活性的差异是由于前者较低的π*轨道，这使得它能够接受来自铜中心的电子密度，形成初始的三元环络合物中间体[HCu(η-CS)]。相比之下，CO则通过氧原子的高电负性促进无势垒的侧基氢化物转移。基于DFT计算，[CuH]与碘甲烷和烯丙基碘反应的侧基S2机制更受青睐。最后，DFT计算得出的[CuH]被甲醇、2,2,2-三氟乙醇和1-丁硫醇质子化的势垒与其气相酸度相关，这表明反应活性主要由底物的酸度控制。
