INSERTION OF ALKYNES INTO THE PD-C BOND OF PALLADACYCLES - MECHANISTIC INFORMATION FROM HIGH-PRESSURE KINETIC AND X-RAY STRUCTURAL DATA
INSERTION OF ALKYNES INTO THE PD-C BOND OF PALLADACYCLES - MECHANISTIC INFORMATION FROM HIGH-PRESSURE KINETIC AND X-RAY STRUCTURAL DATA
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DOI：
10.1021/om00028a063
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发表时间：
1993-04-01
期刊：
影响因子：
2.8
通讯作者：
PFEFFER, M
中科院分区：
文献类型：
--
作者：
RYABOV, AD;VANELDIK, R;PFEFFER, M
本文研究了卤桥环取代的N，N-二甲基苄胺邻钯配合物与[Pd（C6H3RCH2NMe2）X]2 1（R = 4-MeO，5-Me，H，5-F，X = Cl，I）和炔R'C= CR“（R'/R'' = Ph/Ph，Ph/C6H4CF3-3，Ph/C6H4NO2-4，和Et/Et），得到双插入产物3，在25.0-44.1 ℃的氯仿中，在两种试剂浓度下均为一级反应。第一个炔分子的插入是速率决定步骤。1的苯环上的给电子基团R增加了速率常数，Hammett图的斜率等于-2.2。炔的性质的变化导致速率常数的较小和较不系统的变化。在PhC=CPh的情况下，活化体积的范围为-18.6至-14.4cm 3 mol-1，但在EtC=CEt的情况下，活化体积几乎为零。二聚体1被吡啶或[NEt 4] Cl·H2O单体化得到[Pd（C6 H3 RCH 2NMe 2）Cl（L）]（L = py或Cl，电荷被省略），这表明只有二聚体是反应性物种，而卤素桥是炔进入Pd（II）配位平面所必需的。通过与PhC=CPh的反应，对第二个炔的插入进行了动力学研究。 虽然这一步是与顺式->反式重排的C=C键的4，所示的X射线晶体学，其形式的动力学特征是非常相似的第一个插入步骤。这两个步骤都是由苯基或烯基碳原子对配位炔的亲核攻击驱动的。一个更复杂的机制，第二次插入，这是必不可少的占顺->反异构化，进行了详细讨论。
The reaction between halo-bridged ring-substituted orthopalladated NN-dimethylbenzylamines, [Pd(C6H3RCH2NMe2)X]2 1 (R = 4-MeO, 5-Me, H, 5-F, X = Cl, I) and alkynes R'C=CR'' (R'/R'' = Ph/Ph, Ph/C6H4CF3-3, Ph/C6H4NO2-4, and Et/Et) to afford double insertion products 3 is first-order in both the reagent concentrations in chloroform at 25.0-44.1-degrees-C. The insertion of the first alkyne molecule is the rate-determining step. Electron-donating groups R on the phenyl ring of 1 increase the rate constants and the slope of the Hammett plot equals -2.2. Variation of the nature of the alkyne results in smaller and less systematic changes in the rate constants. The volume of activation ranges from -18.6 to -14.4 cm3 mol-1 in the case of PhC=CPh but is practically zero in the case of EtC=CEt. The monomerization of dimers 1 by either pyridine or [NEt4]Cl.H2O to afford the species [Pd(C6H3RCH2NMe2)CI(L)] (L = py or Cl, charges are omitted) retards the insertion markedly, suggesting that only the dimers are the reactive species and that a halo bridge is essential for the entrance of alkyne into the coordination plane of Pd(II). The insertion of the second alkyne was kinetically studied by reacting the seven-membered complex 4 with PhC=CPh. Although this step is associated with a cis --> trans rearrangement about the C=C bond of 4, as shown by X-ray crystallography, its formal kinetic characteristics are very similar to those of the first insertion step. Both the steps are driven by the nucleophilic attack of the phenyl or alkenyl carbon on the coordinated alkyne. A more complicated mechanism of the second insertion, which is essential to account for the cis --> trans isomerization, is discussed in some detail.