Microwave-Assisted Palladium Acetate-Catalyzed C–P Cross-Coupling of Arylboronic Acids and >P(O)H Reagents in the Absence of the Usual Mono- and Bidentate P-Ligands: Mechanistic Insights,The Journal of Organic Chemistry

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Microwave-Assisted Palladium Acetate-Catalyzed C–P Cross-Coupling of Arylboronic Acids and >P(O)H Reagents in the Absence of the Usual Mono- and Bidentate P-Ligands: Mechanistic Insights
The Journal of Organic Chemistry ( IF 3.3 ) Pub Date : 2023-08-09 , DOI: 10.1021/acs.joc.3c01269
Bianka Huszár ₁ , Zoltán Mucsi _{1,

2} , György Keglevich ₁

Affiliation

A less-studied halogen-free variation of the Hirao reaction involving the coupling of arylboronic acids with >P(O)H reagents, such as diarylphosphine oxides, diethyl phosphite, and ethyl phenyl-H-phosphinate, was investigated in detail using Pd(OAc)₂ as the catalyst precursor and applying some excess of the P-reagent to supply the ligand via its trivalent tautomeric (>P–OH) form. The optimum conditions (1.2 equiv of the P-reagent, 135–150 °C, and air) were explored for the synthesis of diaryl-phenylphosphine oxides, aryl-diphenylphosphine oxides, diethyl arylphosphonates, ethyl diphenylphosphinate, and two bisphosphinoyl derivatives. In the reaction of 4-chlorophenyl- or 3-chlorophenylboronic acid with Ph₂P(O)H, triphenylphosphine oxide was also formed as a byproduct. Theoretical calculations suggested that the catalytic cycle of the P–C coupling of PhB(OH)₂ with Ph₂P(O)H is different from that of the usual cross-coupling reactions. It comprises the addition of a phenyl anion and then the tautomeric form >P–OH of the >P(O)H reagent to the Pd²⁺ catalyst complex. This is then followed by reductive elimination affording Ph₃PO that is accompanied with the conversion of Pd²⁺ to Pd⁰. There is a need for a subsequent stoichiometric oxidation of Pd(0) by molecular oxygen. The spontaneous formation of the self-assembling ligands around the Pd²⁺ center from the >P(O)H reactant plays a crucial role in the mechanism and promotes the efficiency of the catalyst.

中文翻译：

在没有常用单齿和双齿 P-配体的情况下，微波辅助乙酸钯催化芳基硼酸和 >P(O)H 试剂的 C-P 交叉偶联：机理见解

使用Pd ( OAc) ₂作为催化剂前体，并应用一些过量的 P 试剂通过其三价互变异构 (>P-OH) 形式提供配体。探索了合成二芳基苯基氧化膦、芳基二苯基氧化膦、芳基膦酸二乙酯、二苯基次膦酸乙酯和两种双膦酰基衍生物的最佳条件（1.2当量的P试剂、135-150°C和空气）。_{在4-氯苯基-或3-氯苯基硼酸与Ph 2} P(O)H的反应中，还形成副产物三苯基氧化膦。_{理论计算表明PhB(OH) 2}与Ph ₂ P(O)H的P-C偶联催化循环与通常的交叉偶联反应不同。它包括添加苯基阴离子，然后将 >P(O)H 试剂的互变异构形式 >P-OH 添加到 Pd ²⁺催化剂络合物中。然后进行还原消除，得到Ph ₃ PO，同时将Pd ²⁺转化为Pd ⁰。需要通过分子氧对 Pd(0) 进行后续化学计量氧化。>P(O)H 反应物在Pd ²⁺中心周围自发形成的自组装配体在该机理中起着至关重要的作用，并提高了催化剂的效率。

更新日期：2023-08-10

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