Oxidative Addition, Transmetalation, and Reductive Elimination at a 2,2′-Bipyridyl-Ligated Gold Center

Three-coordinate
bipyridyl complexes of gold, [(κ2-bipy)­Au­(η2-C2H4)]­[NTf2], are readily
accessed by direct reaction of 2,2′-bipyridine
(bipy), or its derivatives, with the homoleptic gold ethylene complex
[Au­(C2H4)3]­[NTf2]. The
cheap and readily available bipyridyl ligands facilitate oxidative
addition of aryl iodides to the Au­(I) center to give [(κ2-bipy)­Au­(Ar)­I]­[NTf2], which undergo first aryl-zinc
transmetalation and second C–C reductive elimination to produce
biaryl products. The products of each distinct step have been characterized.
Computational techniques are used to probe the mechanism of the oxidative
addition step, offering insight into both the origin of the reversibility
of this process and the observation that electron-rich aryl iodides
add faster than electron-poor substrates. Thus, for the first time,
all steps that are characteristic of a conventional intermolecular
Pd­(0)-catalyzed biaryl synthesis are demonstrated from a common monometallic
Au complex and in the absence of directing groups.

三配位金联吡啶配合物[(κ²-bipy)Au(η²-C₂H₄)][双(三氟甲磺酰)亚胺，NTf₂]可通过2,2′-联吡啶（2,2′-bipyridine，简称bipy）及其衍生物与均配型金乙烯配合物[Au(C₂H₄)₃][NTf₂]直接反应便捷制备。这类廉价易得的联吡啶配体可促进芳基碘化物向一价金（Au(I)）中心的氧化加成反应，生成[(κ²-bipy)Au(Ar)I][NTf₂]；该中间体先后经历芳基-锌转金属化反应与C-C键还原消除步骤，最终生成联芳基产物。各反应步骤的产物均已得到表征。本研究采用计算手段探究氧化加成步骤的反应机理，阐明了该过程可逆性的来源，同时解释了富电子芳基碘化物比缺电子底物反应速率更快的实验现象。因此，本研究首次在普通单金属金配合物体系且无需导向基团的条件下，实现了传统钯(0)催化分子间联芳基合成所涉及的全部特征步骤。