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Intermetallic species in the Negishi coupling and their involvement in inhibition pathways

机译：根岸英一耦合和金属间化合物的物种参与抑制途径

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摘要

The formation of M-Zn-intermetallic species (M = Ni, Pd) in the course of the Negishi reaction in THF solvent and their potential impact on in situ catalyst inhibition were investigated by DFT calculations carried out at two levels of theory. The solvent coordination to the transition metal centers was explicitly accounted for in the calculations. Two model PR3 ligands (PR3 = PMe3 and PPh3), as well as a model NHC-type ligand (1,3-diisopropylimidazol-2-ylidene), were selected. The formation of the intermetallic species during the catalytic process effectively removes the key in-cycle cross-coupling intermediates M(0)L-2, cis-[L2PhM(ii)X], and trans-[L2PhM(ii)X] from the main Negishi catalytic cycle. The reaction between the ZnX2 by-product of the cross-coupling and the M(0)L-2 species yields bi-metallic adducts with M-Zn dative bonds. The nature of these bonds in the resulting complexes was analyzed with QTAIM. ZnX2 coordination to [L2PhM(ii)X] intermediates prevents the binding of alkylzinc halide (RZnX) reagents and blocks the cross-coupling process. Based on these findings, we consider LiX additives as agents that passivate the Lewis-acidic ZnX2 by-product and therefore limit the product inhibition. This work highlights the profound effect of a system view on catalytic cross-coupling reactions, where interactions between components of catalytic systems are taken into account explicitly, and discourage the use of single-cycle-only models.
机译：M-Zn-intermetallic物种的形成(M =倪,Pd)的根岸英一反应四氢呋喃溶剂及其潜在影响原位抑制催化剂由DFT进行调查计算在两个级别的理论。溶剂协调过渡金属中心明确占的计算。和PPh3),以及模型NHC-type配体(1、3-diisopropylimidazol-2-ylidene)选中。物种在催化过程中有效删除关键周期交叉耦合中间体(0)l2, cis - [L2PhM (ii) X],和反式- [L2PhM (ii) X]从主要的根岸英一催化循环。副产品的交叉耦合和M (0) l2物种收益率bi-metallic M-Zn加合物配债券。结果与QTAIM复合物进行了分析。协调[L2PhM (ii) X]中间体防止alkylzinc卤化物的绑定(RZnX)试剂和块交叉耦合过程。基于这些发现,我们认为LiX添加剂代理,使钝化Lewis-acidic ZnX2副产品,因此限制产物抑制。系统对催化产生深远的影响交叉耦合反应,交互组件之间的催化体系考虑明确,鼓励使用single-cycle-only模型。

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