Tiwari Laxmi, Hulley Elliott B, Waynant Kristopher V
Department of Chemistry, University of Idaho, Moscow, Idaho 83844, United States.
Department of Chemistry, University of Wyoming, Laramie, Wyoming 82071, United States.
J Org Chem. 2024 Dec 20;89(24):17917-17925. doi: 10.1021/acs.joc.4c01062. Epub 2024 Dec 4.
Herein, is the reported synthesis and utilization of redox-active arylazoformamide (AAF) ligands in palladium(II) precatalysts for the Suzuki-Miyaura cross-coupling reaction. Complexes were formed from 2 equiv of an AAF ligand with Pd(II)Cl in an appropriate solvent to create the square planar (AAF)PdCl precatalyst. A thorough investigation of aryl bromides and arylboronic acids found that 1.0 mol % precatalyst with cesium carbonate (CsCO) as base, 1,4-dioxane as solvent at 90 °C for 24 h allowed for excellent conversions to the biphenyl products (over 20 examples). To highlight the AAF ligand class, a set of comparison reactions were performed with redox-active arylazothioformamide ligands, i.e., an (ATF)PdCl complex, other commercial palladium(II) complexes, and a Ni(II)Cl arylazoformamide coordination complex. The (AAF)PdCl complexes outperformed all of others tested. Mechanistically, it is proposed that the AAF ligand singly reduces to antiferromagnetically couple to the palladium(I) complex as a transmetalation intermediate. Ni-based precatalysts were found to be inactive for the studied Suzuki-Miyaura reaction. Overall, these ligand systems offer a unique look into redox-active palladium cross-coupling reactions as well as being phosphine-free and high yielding.
本文报道了氧化还原活性芳基偶氮甲酰胺（AAF）配体在钯（II）预催化剂中用于铃木-宫浦交叉偶联反应的合成与应用。在适当的溶剂中，由2当量的AAF配体与Pd（II）Cl形成配合物，以制备平面正方形的（AAF）PdCl预催化剂。对芳基溴化物和芳基硼酸进行的深入研究发现，以碳酸铯（Cs₂CO₃）为碱、1,4-二氧六环为溶剂、在90℃下反应24小时，使用1.0摩尔%的预催化剂可实现对联苯产物的优异转化（超过20个实例）。为突出AAF配体类别，进行了一组与氧化还原活性芳基偶氮硫代甲酰胺配体（即（ATF）PdCl配合物）、其他商业钯（II）配合物以及Ni（II）Cl芳基偶氮甲酰胺配位配合物的对比反应。（AAF）PdCl配合物的性能优于所有其他测试对象。从机理上讲，有人提出AAF配体单电子还原后作为反金属化中间体与钯（I）配合物反铁磁耦合。发现镍基预催化剂对所研究的铃木-宫浦反应无活性。总体而言，这些配体体系为氧化还原活性钯交叉偶联反应提供了独特视角，且不含膦且产率高。
