BINAP-配位钯配合物催化芳基卤胺化机理的再评价,Journal of the American Chemical Society

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BINAP-配位钯配合物催化芳基卤胺化机理的再评价
Journal of the American Chemical Society ( IF 14.4 ) Pub Date : 2006-03-01 , DOI: 10.1021/ja045533c
Shashank Shekhar , Per Ryberg , John F. Hartwig , Jinu S. Mathew , Donna G. Blackmond , Eric R. Strieter , Stephen L. Buchwald

两项研究的作者都重新审查了之前的两项关于由 1,1'-联萘-2,2'-二基双（二苯基膦）（BINAP）的钯配合物催化的芳基卤化物胺化的机理研究。目前的工作包括对胺与芳基卤化物反应中存在的 BINAP 连接的钯配合物的身份的详细研究，以及这些催化反应的速率测量，这些催化反应是用纯预催化剂和由 [Pd2(dba)3] 原位生成的预催化剂引发的。比纳普。这项工作揭示了之前两项研究中的错误，我们描述了我们目前对这种具有综合重要性的转变机制的理解状态。31P NMR 光谱表明，当催化剂由 [Pd2(dba)3] 和 BINAP 原位生成时，催化体系中存在几种钯 (0) 物种，并且这些复合物中至少有两个会产生催化中间体。此外，这些光谱研究和伴随的动力学数据表明，仲胺反应过程中胺浓度的明显正序最好归因于催化剂分解。对分离的预催化剂的动力学研究表明，催化反应的速率与胺的种类和浓度无关，而对原位生成的催化剂的研究表明，这些反应的速率与胺的浓度无关。此外，发现由 [Pd(BINAP)2] 与添加的 BINAP 催化的反应在溴芳烃中是一级反应，而在配体中是反向一级反应，这与之前表明两者均为零级动力学的工作相反。这些数据，以及溴苯在催化反应中的衰减与根据化学计量氧化加成研究的速率常数预测的溴苯衰减之间的相关性，与溴芳烃氧化加成到 [Pd(BINAP) ] 在胺配位之前，其中 [Pd(BINAP)2]，通过 BINAP 的解离生成 [Pd(BINAP)]，处于循环之外。通过这种机制，胺和碱与 [Pd(BINAP)(Ar)(Br)] 反应形成芳基钯酰氨基络合物，然后从该酰氨基络合物中还原消除形成芳胺。与催化过程一致，其中溴芳烃在胺配位之前发生氧化加成到 [Pd(BINAP)]，其中 [Pd(BINAP)2] 通过 BINAP 的解离生成 [Pd(BINAP)]，不在循环中。通过这种机制，胺和碱与 [Pd(BINAP)(Ar)(Br)] 反应形成芳基钯酰氨基络合物，然后从该酰氨基络合物中还原消除形成芳胺。与催化过程一致，其中溴芳烃在胺配位之前发生氧化加成到 [Pd(BINAP)]，其中 [Pd(BINAP)2] 通过 BINAP 的解离生成 [Pd(BINAP)]，不在循环中。通过这种机制，胺和碱与 [Pd(BINAP)(Ar)(Br)] 反应形成芳基钯酰氨基络合物，然后从该酰氨基络合物中还原消除形成芳胺。

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Reevaluation of the Mechanism of the Amination of Aryl Halides Catalyzed by BINAP-Ligated Palladium Complexes

Two previous mechanistic studies of the amination of aryl halides catalyzed by palladium complexes of 1,1'-binaphthalene-2,2'-diylbis(diphenylphosphine) (BINAP) are reexamined by the authors of both studies. This current work includes a detailed study of the identity of the BINAP-ligated palladium complexes present in reactions of amines with aryl halides and rate measurements of these catalytic reactions initiated with pure precatalysts and precatalysts generated in situ from [Pd2(dba)3] and BINAP. This work reveals errors in both previous studies, and we describe our current state of understanding of the mechanism of this synthetically important transformation. 31P NMR spectroscopy shows that several palladium(0) species are present in the catalytic system when the catalyst is generated in situ from [Pd2(dba)3] and BINAP, and that at least two of these complexes generate catalytic intermediates. Further, these spectroscopic studies and accompanying kinetic data demonstrate that an apparent positive order in the concentration of amine during reactions of secondary amines is best attributed to catalyst decomposition. Kinetic studies with isolated precatalysts show that the rates of the catalytic reactions are independent of the identity and the concentration of amine, and studies with catalysts generated in situ show that the rates of these reactions are independent of the concentration of amine. Further, reactions catalyzed by [Pd(BINAP)2] with added BINAP are found to be first-order in bromoarene and inverse first-order in ligand, in contrast to previous work indicating zero-order kinetics in both. These data, as well as a correlation between the decay of bromobenzene in the catalytic reaction and the predicted decay of bromobenzene from rate constants of studies on stoichiometric oxidative addition, are consistent with a catalytic process in which oxidative addition of the bromoarene occurs to [Pd(BINAP)] prior to coordination of amine and in which [Pd(BINAP)2], which generates [Pd(BINAP)] by dissociation of BINAP, lies off the cycle. By this mechanism, the amine and base react with [Pd(BINAP)(Ar)(Br)] to form an arylpalladium amido complex, and reductive elimination from this amido complex forms the arylamine.

更新日期：2006-03-01

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