Adamo Carlo, Amatore Christian, Ciofini Ilaria, Jutand Anny, Lakmini Hakim
Ecole Nationale Supérieure de Chimie, Laboratoire d'Electrochimie et Chimie Analytique, UMR CNRS 7575, 11 Rue Pierre et Marie Curie, F-75231 Paris Cedex 5, France.
J Am Chem Soc. 2006 May 31;128(21):6829-36. doi: 10.1021/ja0569959.
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 fully elucidated. The peroxo complex (eta(2)-O(2))PdL(2) (L = PPh(3)), generated in the reaction of dioxygen with the Pd(0) catalyst, was found to play a crucial role. Indeed, it reacts with the arylboronic acid to generate an adduct (coordination of one oxygen atom of the peroxo complex to the oxophilic boron atom of the arylboronic acid) characterized by (31)P NMR spectroscopy and ab initio calculations. This adduct reacts with a second molecule of arylboronic acid to generate trans-ArPd(OH)L(2) complexes. A transmetalation by the arylboronic acid gives trans-ArPdArL(2) complexes. The biaryl is then released in a reductive elimination. This reaction is at the origin of the formation of biaryls as byproducts in palladium-catalyzed Suzuki-Miyaura reactions when they are not conducted under oxygen-free atmosphere.
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机理已得到充分阐明。发现氧气与Pd(0)催化剂反应生成的过氧配合物(η²-O₂)PdL₂（L = PPh₃）起着关键作用。实际上，它与芳基硼酸反应生成一种加合物（过氧配合物的一个氧原子与芳基硼酸的亲氧硼原子配位），通过³¹P NMR光谱和从头算计算对其进行了表征。该加合物与第二个芳基硼酸分子反应生成反式-ArPd(OH)L₂配合物。芳基硼酸进行转金属化反应生成反式-ArPdArL₂配合物。然后通过还原消除反应释放出联芳基。当钯催化的铃木-宫浦反应不在无氧气氛下进行时，该反应是联芳基作为副产物形成的根源。
