EaStChem, University of Edinburgh, Joseph Black Building, David Brewster Road, Edinburgh EH9 3FJ, U.K.
J Am Chem Soc. 2022 Aug 24;144(33):15372-15382. doi: 10.1021/jacs.2c06831. Epub 2022 Aug 15.
The Ni/Ir-photocatalyzed coupling of an aryl bromide (ArBr) with an alkyl bromide (RBr) has been analyzed using LED-F NMR spectroscopy. Four components (light, [ArBr], [Ni], [Ir]) are found to control the rate of ArBr consumption, but not the product selectivity, while two components ([(TMS)SiH], [RBr]) independently control the product selectivity, but not the rate. A major resting state of nickel has been identified as ArNi(L)Br, and C-isotopic entrainment is used to show that the complex undergoes Ir-photocatalyzed conversion to products (Ar-R, Ar-H, Ar-solvent) in competition with the release of ArBr. A range of competing absorption and quenching effects lead to complex correlations between the Ir and Ni catalyst loadings and the reaction rate. Differences in the Ir/Ni Beer-Lambert absorption profiles allow the rate to be increased by the use of a shorter-wavelength light source without compromising the selectivity. A minimal kinetic model for the process allows simulation of the reaction and provides insights for optimization of these processes in the laboratory.
采用 LED-F NMR 光谱法分析了 Ni/Ir 光催化芳基溴化物（ArBr）与烷基溴化物（RBr）偶联。发现有四个组分（光、[ArBr]、[Ni]、[Ir]）控制着 ArBr 消耗的速率，但不控制产物的选择性，而两个组分（[(TMS)SiH]、[RBr]）独立地控制着产物的选择性，但不控制速率。镍的主要休眠状态已被确定为 ArNi(L)Br，并利用 C 同位素跟踪表明，该配合物在 Ir 光催化下与 ArBr 的释放相竞争，转化为产物（Ar-R、Ar-H、Ar-溶剂）。一系列竞争的吸收和猝灭效应导致 Ir 和 Ni 催化剂负载与反应速率之间存在复杂的相关性。Ir/Ni 的 Beer-Lambert 吸收曲线的差异允许使用更短波长的光源来提高速率，而不会影响选择性。该过程的最小动力学模型允许对反应进行模拟，并为在实验室中优化这些过程提供了深入的见解。
