Kinetic Data for the Transmetalation/Reductive Elimination in Palladium-Catalyzed Suzuki-Miyaura Reactions: Unexpected Triple Role of Hydroxide Ions Used as Base
Kinetic Data for the Transmetalation/Reductive Elimination in Palladium-Catalyzed Suzuki-Miyaura Reactions: Unexpected Triple Role of Hydroxide Ions Used as Base
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DOI：
10.1002/chem.201001911
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发表时间：
2011-02-01
影响因子：
4.3
通讯作者：
Le Duc, Gaetan
中科院分区：
文献类型：
--
作者：
Amatore, Christian;Jutand, Anny;Le Duc, Gaetan
在真实的钯催化的Suzuki-Miyaura反应中，建立了反式-[ArPdX（PPh 3）（2）]（Ar=p-Z-C6 H4; Z=CN，F，H; X=I，Br，Cl）与Ar 'B（OH）（2）（Ar'= p-Z '-C6 H4; Z'= CN，H，OMe）在DMF中碱OH-存在下的反应机理.通过电化学技术的应用，追踪了交叉偶联产物ArAr'和[Pd-0（PPh 3）（3）]的形成。动力学数据已获得的第一次，所观察到的速率常数，k（obs），整体反应的测定。反式-[ArPdX（PPh 3）（2）]在不存在碱的情况下不反应。碱OH-起三种作用。它有利于反应：1）通过形成反式[ArPd（OH）（PPh 3）（2）]，与反式-[ArPdX（PPh 3）（2）]相反，反式[ArPdX（PPh 3）（2）]与Ar 'B（OH）（2）反应的关键络合物（速率决定性金属转移），和2）通过意外促进从中间体反式-[ArPdAr'（PPh 3）（2）]的还原消除，其产生ArAr'和Pd-O物质。相反，碱OH-通过形成非反应性阴离子Ar 'B（OH）（3）（-）而不利于反应。作为OH-的这些拮抗作用的结果，总体反应性由OH-的浓度控制，并且随着OH-浓度的增加而通过最大值。因此，碱有利于速率决定的金属转移，也出乎意料地有利于还原消除。
The mechanism of the reaction of trans-[ArPdX(PPh3)(2)] (Ar=p-Z-C6H4; Z=CN, F, H; X=I, Br, Cl) with Ar'B(OH)(2) (Ar'=p-Z'-C6H4; Z'=CN, H, OMe) has been established in DMF in the presence of the base OH- in the context of real palladium-catalyzed Suzuki-Miyaura reactions. The formation of the cross-coupling product ArAr' and [Pd-0(PPh3)(3)] has been followed through the application of electrochemical techniques. Kinetic data have been obtained for the first time, with determination of the observed rate constant, k(obs), of the overall reaction. trans-[ArPdX(PPh3)(2)] is not reactive in the absence of the base. The base OH- plays three roles. It favors the reaction: 1) by formation of trans[ArPd(OH)(PPh3)(2)], a key complex which, in contrast to trans-[ArPdX(PPh3)(2)], reacts with Ar'B(OH)(2) (rate-determining transmetalation), and 2) by unexpected promotion of the reductive elimination from the intermediate trans-[ArPdAr'(PPh3)(2)], which generates ArAr' and a Pd-0 species. Conversely, the base OH- disfavors the reaction by formation of the unreactive anionic Ar'B(OH)(3)(-). As a consequence of these antagonistic effects of OH-, the overall reactivity is controlled by the concentration of OH- and passes through a maximum as the concentration of OH- is increased. Therefore, the base favors the rate-determining transmetalation and unexpectedly also the reductive elimination.