Department of Chemistry, Faculty of Mathematics and Natural Sciences, Universitas Padjadjaran, 45363 Jatinangor, Indonesia.
J Am Chem Soc. 2020 Apr 1;142(13):6036-6050. doi: 10.1021/jacs.9b11871. Epub 2020 Mar 18.
C-C reductive elimination from [PdL(CF)] to form polyfluorinated biaryls has been a challenge for over 50 years. Thus, palladium-catalyzed homocoupling of arylboronates (Ar-Bpin) containing two -fluorine substituents is very difficult, as the reaction typically stops at the [PdL(Ar)] stage after two transmetalation steps. The transmetalated complexes [Pd(MeCN)(CF)] (), [Pd(MeCN)(2,4,6-CFH)] (), and -[Pd(MeCN)(2,6-CFH)] () have been isolated from the reaction of Ar-Bpin with Pd(OAc) in acetonitrile solvent, with no homocoupling observed. However, catalytic homocoupling proceeds smoothly in a "weakly coordinating" arene solvent as long as no ancillary ligands or coordinating solvents are present. DFT computations reveal that the active catalyst formed by arene solvent coordination leads to an overall reduced barrier for the reductive elimination step compared to the formation of stable [PdL(Ar)] complexes in the presence of a donor ligand or solvent L.
C-C 还原消除生成多氟联芳烃的反应已经有 50 多年的历史了。因此，含有两个氟取代基的芳基硼酸酯（Ar-Bpin）的钯催化交叉偶联反应非常困难，因为在经过两步转金属化步骤后，反应通常在[PdL(Ar)]阶段停止。从 Ar-Bpin 与 Pd(OAc)在乙腈溶剂中的反应中分离出了transmetalated 配合物[Pd(MeCN)(CF)] ()、[Pd(MeCN)(2,4,6-CFH)] ()和-[Pd(MeCN)(2,6-CFH)] ()，但没有观察到自偶联反应。然而，只要不存在辅助配体或配位溶剂，在“弱配位”芳烃溶剂中，催化自偶联反应就能顺利进行。DFT 计算表明，与存在给体配体或溶剂 L 时形成稳定的[PdL(Ar)]配合物相比，芳基溶剂配位形成的活性催化剂导致还原消除步骤的总势垒降低。
