Reevaluation of the mechanism of the amination of aryl halides catalyzed by BINAP-ligated palladium complexes
Reevaluation of the mechanism of the amination of aryl halides catalyzed by BINAP-ligated palladium complexes
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DOI：
10.1021/ja045533c
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发表时间：
2006-03-22
影响因子：
15
通讯作者：
Buchwald, SL
中科院分区：
文献类型：
--
作者：
Shekhar, S;Ryberg, P;Buchwald, SL
对1，1 '-联萘-2，2'-二基双（二苯基膦）钯配合物催化芳基卤胺化反应的机理进行了重新研究。目前的工作包括详细研究胺与芳基卤化物反应中存在的BINAP连接的钯络合物的身份，以及用纯预催化剂和由[Pd-2（dba）（3）]和BINAP原位生成的预催化剂引发的这些催化反应的速率测量。这项工作揭示了在以前的研究中的错误，我们描述了我们目前的理解这种综合重要的转变的机制。P-31 NMR光谱表明，当催化剂由[Pd-2（dba）（3）]和BINAP原位生成时，催化体系中存在几种钯（O）物质，并且这些络合物中的至少两种生成催化中间体。此外，这些光谱研究和伴随的动力学数据表明，在仲胺反应期间胺浓度的表观正序最好归因于催化剂分解。动力学研究与分离的预催化剂表明，催化反应的速率是独立的身份和胺的浓度，和原位生成的催化剂的研究表明，这些反应的速率是独立的胺的浓度。此外，发现由[Pd（BINAP）（2）]与添加的BINAP催化的反应在溴代芳烃中为一级反应，在配体中为反一级反应，与先前的工作表明两者均为零级动力学相反。这些数据以及催化反应中溴苯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催化过程一致，其中溴代芳烃在胺配位之前发生氧化加成到[Pd（BINAP）]，并且其中[Pd（BINAP）（2）]通过BINAP的解离产生[Pd（BINAP）]，从周期中消失。通过该机理，胺和碱与[Pd（BINAP）（Ar）（Br）]反应以形成芳基钯酰胺基络合物，并且从该酰胺基络合物还原消除形成芳基胺。
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 [Pd-2(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. P-31 NMR spectroscopy shows that several palladium(O) species are present in the catalytic system when the catalyst is generated in situ from [Pd-2(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.