Materials and Process Simulation Center, California Institute of Technology, Pasadena, California 91125, USA.
J Am Chem Soc. 2011 Sep 14;133(36):14293-300. doi: 10.1021/ja2012627. Epub 2011 Aug 23.
We present a detailed study of the mechanism for oxidative heteroarylation, based on DFT calculations and experimental observations. We propose binuclear Au(II)-Au(II) complexes to be key intermediates in the mechanism for gold catalyzed oxidative heteroarylation. The reaction is thought to proceed via a gold redox cycle involving initial oxidation of Au(I) to binuclear Au(II)-Au(II) complexes by Selectfluor, followed by heteroauration and reductive elimination. While it is tempting to invoke a transmetalation/reductive elimination mechanism similar to that proposed for other transition metal complexes, experimental and DFT studies suggest that the key C-C bond forming reaction occurs via a bimolecular reductive elimination process (devoid of transmetalation). In addition, the stereochemistry of the elimination step was determined experimentally to proceed with complete retention. Ligand and halide effects played an important role in the development and optimization of the catalyst; our data provides an explanation for the ligand effects observed experimentally, useful for future catalyst development. Cyclic voltammetry data is presented that supports redox synergy of the Au···Au aurophilic interaction. The monometallic reductive elimination from mononuclear Au(III) complexes is also studied from which we can predict a ~15 kcal/mol advantage for bimetallic reductive elimination.
我们基于 DFT 计算和实验观察，对氧化杂芳基化的机理进行了详细研究。我们提出双核 Au(II)-Au(II)配合物是金催化氧化杂芳基化机理中的关键中间体。该反应被认为通过涉及初始氧化 Au(I)至双核 Au(II)-Au(II)配合物的金氧化还原循环进行，该配合物由 Selectfluor 进行，随后进行杂芳基化和还原消除。虽然引入类似于其他过渡金属配合物所提出的转金属/还原消除机制很诱人，但实验和 DFT 研究表明，关键的 C-C 键形成反应是通过双分子还原消除过程（没有转金属）发生的。此外，实验确定消除步骤的立体化学以完全保留的方式进行。配体和卤化物效应对催化剂的开发和优化起着重要作用；我们的数据为实验中观察到的配体效应提供了解释，这对未来的催化剂开发很有用。还提出了支持 Au···Au 金亲相互作用的氧化还原协同作用的循环伏安数据。还研究了单核 Au(III)配合物的单金属还原消除，从中我们可以预测双金属还原消除具有约 15 kcal/mol 的优势。
