Lakmini H, Ciofini I, Jutand A, Amatore C, Adamo C
Département de Chimie, Ecole Normale Supérieure, UMR CNRS-ENS-UPMC 8640, 24 Rue Lhomond, F-75231 Paris Cedex 5, France.
J Phys Chem A. 2008 Dec 18;112(50):12896-903. doi: 10.1021/jp801948u.
The key step in the mechanism of the Palladium-catalyzed homocoupling of arylboronic acids ArB(OH)(2)(Ar = 4-Z-C(6)H(4) with Z = MeO, H, CN) in the presence of dioxygen, leading to symmetrical biaryls, has been elucidated by using density functional theory. In particular, by starting from the peroxo complex O(2)PdL(2)(L = PPh(3)), generated in the reaction of dioxygen with the Pd(0) catalyst, the fundamental role played by an intermediate formed by coordination of one oxygen atom of the peroxo complex to the oxophilic boron atom of the arylboronic acid has been pointed out. This adduct reacts with a second molecule of arylboronic acid to generate a cis-Ar-Pd(OOB(OH)(2))L(2) complex that can form the stable intermediate trans-Ar-Pd(OH)L(2) (experimentally characterized) through a sequence of hydrolysis and isomerization reactions. All theoretical insights are in agreement and do substantiate the experimentally postulated mechanism. Furthermore, direct comparison of experimental and computed spectroscopic parameters (here, (31)P chemical shifts) allows us to confirm the formation of the intermediate.
在氧气存在下，钯催化芳基硼酸ArB(OH)₂（Ar = 4-Z-C₆H₄，Z = MeO、H、CN）发生均偶联反应生成对称联芳基的关键步骤，已通过密度泛函理论得以阐明。具体而言，从氧气与Pd(0)催化剂反应生成的过氧配合物O₂PdL₂（L = PPh₃）出发，指出了过氧配合物的一个氧原子与芳基硼酸的亲氧硼原子配位形成的中间体所起的重要作用。该加合物与第二分子芳基硼酸反应生成顺式-Ar-Pd(OOB(OH)₂)L₂配合物，该配合物可通过一系列水解和异构化反应形成稳定的中间体反式-Ar-Pd(OH)L₂（已通过实验表征）。所有理论见解均一致，并确实证实了实验推测的机理。此外，对实验和计算得到的光谱参数（此处为³¹P化学位移）进行直接比较，使我们能够确认中间体的形成。
