The functionalization of CO₂ mediated by a series of U(IV) mixed-sandwich compounds, (COT^TIPS2)Cp*UR (R = −CH₃, −CH₂Ph, −CH₂TMS, −CH(TMS)₂, −NHPh, −OPh, −SPh, −SePh; COT^TIPS2 = C₈H₆(SiⁱPr₃-1,4)₂; Cp* = C₅Me₅; TMS = SiMe₃), was investigated by the density functional theory method. A two-step mechanism was revealed, in which the insertion of CO₂ 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^TIPS2)Cp*UCH₃ 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 CO₂ functionalization was also compared and discussed. The results were consistent with experimental studies and complemented with molecular level of understanding on the mechanisms of CO₂ functionalization promoted by tetravalent U complexes.

中文翻译：

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密度泛函理论评价四价铀配合物介导的CO ₂功能化的影响因素

CO的官能₂由一系列U（IV）混合夹心化合物，（COT介导^TIPS2）的Cp * UR（R = -CH ₃，-CH ₂ PH，-CH ₂ TMS，-CH（TMS）₂， -NHPh，-OPh，-SPh，-SePh; COT ^TIPS2 = C ₈ H ₆（Si ⁱ Pr ₃ -1,4）₂ ; Cp * = C ₅ Me ₅ ; TMS = SiMe ₃）功能理论方法。揭示了一个两步机制，其中CO ₂的插入通过过渡态的速率决定步骤是确定进入UC键的步骤，该过渡态的特征是四元环具有18.8 kcal / mol的自由能垒，对（COT ^TIPS2）Cp * UCH ₃系统的反应。整个反应以45.0kcal / mol强烈放热。讨论了取代作用，包括R基团的庞大性和连接原子的性质，发现空间位阻和静电相互作用是所观察到的反应性变化的原因。还比较和讨论了U（III）和U（IV）配合物在CO ₂功能化中的反应性。结果与实验研究一致，并且对CO ₂机理的分子水平有补充。 四价U配合物促进了功能化。