Carbon-nitrogen-bond-forming reductive elimination of arylamines from palladium(II) phosphine complexes
Carbon-nitrogen-bond-forming reductive elimination of arylamines from palladium(II) phosphine complexes
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DOI：
10.1021/ja971057x
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发表时间：
1997-09-03
影响因子：
15
通讯作者：
Hartwig, JF
中科院分区：
文献类型：
--
作者：
Driver, MS;Hartwig, JF
反式-（PPh 3）（2）Pd（Ar）（NAr ′（2））和（DPPF）-Pd（Ar）（NAr ′（2））形式的一系列单体钯酰胺络合物（DPPF = 1，1 '-双（二苯基膦基）二茂铁）和{（PPh 3）Pd（Ar）（μ-NHR）}形式的二聚钯酰胺络合物（2）（R = Ph，t-Bu）是通过氨基化锂和氨基化钾与钯芳基卤化物配合物反应制备的，获得了（DPPF）Pd（p-NMe_2C_6 H_4）[N（p-CH_3C_6 H_4）（2）]的X射线晶体结构。在PPh 3作为捕集剂存在下，单体和二聚体钯酰胺络合物在热处理后均经历形成C-N键的还原消除，从而以高收率沿着Pd（0）物质形成芳胺。在室温下，还观察到从氮杂金属配合物（PPh_3）Pd（eta（2）-C_6H_4C_6H_4- NH）的还原消除，以形成咔唑和Pd（PPh_3）（4）。对单体PPh 3-连接的酰胺基络合物的还原消除反应的机理研究表明，存在两种竞争途径形成胺。在低[PPh 3]，还原消除发生通过膦解离，形成一个三配位的中间体;然而，随着[PPh 3]的增加，从四配位络合物的还原消除途径成为主导。DPPF配位的钯酰胺络合物直接消除了四配位络合物中的胺。研究了二聚钯酰胺配合物的还原消除反应机理。这些配合物通过二聚体解离进行胺的还原消除，以产生类似于由PPh 3连接的单体酰胺基配合物形成的三配位中间体。C-N-键形成的还原消除反应被加速的吸电子基团上的Pd结合的芳基基团和供电子基团上的酰胺基配体，这表明芳基基团作为亲电试剂和酰胺基配体作为亲核试剂。
A series of monomeric palladium amido complexes of the form trans-(PPh3)(2)Pd(Ar)(NAr'(2)) and (DPPF)-Pd(Ar)(NAr'(2)) (DPPF = 1,1'-bis(diphenylphosphino)ferrocene) and dimeric palladium amido complexes of the form {(PPh3)Pd(Ar)(mu-NHR)}(2) (R = Ph, t-Bu) have been prepared by the reaction of lithium and potassium amides with palladium aryl halide complexes, An X-ray crystal structure of (DPPF)Pd(p-NMe2C6H4)[N(p-CH3C6H4)(2)] was obtained. Upon thermolysis in the presence of PPh3, serving as a trapping agent, both the monomeric and dimeric palladium amido complexes underwent C-N-bond-forming reductive elimination to form arylamines in high yields along with a Pd(0) species. Reductive elimination was also observed from azametallacycle (PPh3)Pd(eta(2)-C6H4C6H4- NH), to form carbazole and Pd(PPh3)(4) at room temperature. Mechanistic studies on the reductive elimination reactions of the monomeric PPh3-ligated amido complexes indicated the presence of two competing pathways for the formation of amine. At low [PPh3], reductive elimination occurs via phosphine dissociation to form a three-coordinate intermediate; however, as [PPh3] is increased, a pathway of reductive elimination from a four-coordinate complex becomes dominant. The DPPF-ligated palladium amido complexes directly eliminated amine from the four-coordinate complex. The mechanism of the reductive elimination from dimeric palladium amido complexes was also studied. These complexes undergo reductive elimination of amine via dimer dissociation to generate a three-coordinate intermediate analogous to those formed by the PPh3-ligated monomeric amido complexes. The C-N-bond forming reductive elimination reactions were accelerated by electron-withdrawing groups on the Pd bound aryl group and by electron-donating groups on the amido ligand, suggesting that the aryl group acts as an electrophile and the amido ligand acts as a nucleophile.