Nickel Hydroxo Complexes as Intermediates in Nickel-Catalyzed Suzuki–Miyaura Cross-Coupling

The synthesis, characterization, and reactivity of intermediates formed in the Ni-catalyzed Suzuki–Miyaura cross-coupling (SMC) of an aryl chloride are described. Oxidative addition of 1-chloro-4-trifluoromethylbenzene (1) to a mixture of Ni­(cod)2 and PCy3 afforded NiCl­(4-CF3Ph)­(PCy3)2 (2), which then cleanly provided dimeric [Ni­(4-CF3Ph)­(μ–OH)­(PCy3)]2 (3) by reaction with aqueous KOH. Reactivity studies of 2 and 3 with phenylboronic acid (4) revealed that, while 2 affords only traces of the biphenyl coupling product after 24 h, the same reaction with 3 is complete within minutes at room temperature. In contrast, the reaction of 3 with potassium phenyltrihydroxyborate (6) is much slower than that with boronic acid 4, and significantly lower yields of the cross-coupling product are obtained. We show that formation of the hydroxo species 3 is the rate-determining step in the present SMC.

本文报道了芳基氯参与的镍催化铃木-宫浦交叉偶联反应（Suzuki–Miyaura cross-coupling，SMC）中所生成中间体的合成、表征及反应性能研究。将1-氯-4-三氟甲基苯（1）与Ni(cod)₂和三环己基膦（PCy3）的混合物进行氧化加成，得到配合物NiCl(4-CF3Ph)(PCy3)₂（2）；随后该配合物与氢氧化钾水溶液反应，可专一性生成二聚体桥联羟基配合物[Ni(4-CF3Ph)(μ–OH)(PCy3)]₂（3）。对配合物2与3分别与苯硼酸（4）的反应性能进行研究后发现，尽管配合物2在24小时后仅能生成痕量联苯偶联产物，但配合物3参与的同款反应可在室温条件下数分钟内完全完成；与之相对，配合物3与苯三羟基硼酸钾（6）的反应速率远低于其与苯硼酸（4）的反应，且最终得到的交叉偶联产物收率显著更低。本研究证实，羟基桥联二聚体3的生成是当前研究的铃木-宫浦交叉偶联反应的决速步。