Liu Yanxiao, Liu Ruozhuang, Ding Wanjian, Wang Dongqi
Key Laboratory of Theoretical and Computational Photochemistry, Ministry of Education, College of Chemistry, Beijing Normal University, Beijing 100875, China.
Multidisciplinary Initiative Center, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China.
J Phys Chem A. 2020 Apr 2;124(13):2683-2693. doi: 10.1021/acs.jpca.0c00724. Epub 2020 Mar 20.
The functionalization of CO mediated by a series of U(IV) mixed-sandwich compounds, (COT)CpUR (R = -CH, -CHPh, -CHTMS, -CH(TMS), -NHPh, -OPh, -SPh, -SePh; COT = CH(SiPr-1,4); Cp = CMe; TMS = SiMe), was investigated by the density functional theory method. A two-step mechanism was revealed, in which the insertion of CO into the U-C bond was identified as the rate-determining step via a transition state featured by a four-membered ring with a free-energy barrier of 18.8 kcal/mol to the reaction of the (COT)Cp*UCH system. The whole reaction was strongly exothermic by 45.0 kcal/mol. Substitution effect was discussed, including the bulkiness of the R group and the nature of the ligating atom, and steric hindrance and electrostatic interactions were found to be responsible for the observed variation in reactivity. The reactivity of U(III) and U(IV) complexes in CO functionalization was also compared and discussed. The results were consistent with experimental studies and complemented with molecular level of understanding on the mechanisms of CO functionalization promoted by tetravalent U complexes.
