Variable-temperature and -pressure kinetics and mechanism of the cyclopalladation reaction of imines in aprotic solvent
Variable-temperature and -pressure kinetics and mechanism of the cyclopalladation reaction of imines in aprotic solvent
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DOI：
10.1021/om961099e
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发表时间：
1997-06-10
期刊：
影响因子：
2.8
通讯作者：
Martinez, M
中科院分区：
文献类型：
--
作者：
Gomez, M;Granell, J;Martinez, M
本文研究了苯亚甲基苄胺、苯亚甲基苯胺和苯亚甲基丙胺与乙酸钯在甲苯溶液中的环化反应。环化化合物通过C-H亲电键活化形成，以产生不同类型的金属杂环，这取决于所选配体的多官能性质。如果五元内型金属配位化合物是可能的，则其通过芳族C-H键活化形成。只有当内环化需要通过脂肪族C-H键活化形成六元化合物时，或者当空间位阻以重要的方式影响亚胺的平面性时，才会形成五元外金属配合物。只有当替代的芳香族C-H键活化会产生四元外环化合物时，才能实现内六元金属杂环的脂肪族C-H键活化;没有观察到脂肪族C-H键活化形成内五元络合物。在不同的温度和压力下的反应进行了动力学监测，以建立这些自发反应发生的机制。从获得的结果中可以明显看出三组不同的激活参数：与苄胺和丙胺有关的那些（Δ H-双刃= +45/+67 kJ mol（-1），Δ S-双刃= -100/-180 J K-1 mol（-1），Δ V-双刃= -11/-17 cm（3）mol（-1）），与苯胺衍生物有关的那些（Δ H-双刃= +66/+75 kJ mol（-1），Δ S-双刃= -96/-123 J K-1 mol（-1），Δ V-双刃= -21/-25 cm（3）mol（-1）），最后是与亚胺产生脂肪键活化有关的那些（Δ H-双匕首= +48/+49 kJ mol（-1），Δ S-双匕首= -167/-177 J K-1 mol（-1），Δ V-双匕首= -20/-24 cm（3）mol（-1））。结果被解释为一个高度有序的四中心过渡态的形成，涉及C-H和Pd-O（乙酰基）键，这被发现是非常敏感的灵活性和空间位阻的亚胺配体和C-H键的电子变化非常不敏感。
The cyclometalation reactions of benzylidenebenzylamines, -anilines, and -propylamine with palladium acetate have been studied in toluene solution. The cyclometalated compounds are formed via C-H electrophilic bond activation to produce different types of metallacycles, depending upon the polyfunctional nature of the ligand selected. If a five-membered endo metallacycle is possible, it is formed via aromatic C-H bond activation. Formation of a five-membered exo metallacycle only takes place when endo cyclometalation requires the formation of a six-membered compound via aliphatic C-H bond activation or when the steric hindrance affects the planarity of the imine in an important way. The activation of aliphatic C-H bonds has been achieved for endo six-membered metallacycles only when the alternative aromatic C-H bond activation would produce a four-membered exo compound; no activation of aliphatic C-H bonds to form endo five-membered complexes has been observed. The reactions have been monitored kinetically at different temperatures and pressures in order to establish the mechanism through which these spontaneous reactions occur. Three different sets of activation parameters are apparent from the results obtained: those related to the benzylamines and propylamine (Delta H-double dagger = +45/+67 kJ mol(-1), Delta S-double dagger = -100/-180 J K-1 mol(-1), Delta V-double dagger = -11/-17 cm(3) mol(-1)), those related to the aniline derivatives (Delta H-double dagger = +66/+75 kJ mol(-1), Delta S-double dagger = -96/-123 J K-1 mol(-1), Delta V-double dagger = -21/-25 cm(3) mol(-1)), and finally those related to the imines producing aliphatic bond activation (Delta H-double dagger = +48/+49 kJ mol(-1), Delta S-double dagger = -167/-177 J K-1 mol(-1), Delta V-double dagger = -20/-24 cm(3) mol(-1)). The results are interpreted as the formation of a highly ordered four-center transition state, involving the C-H and Pd-O(acetato) bonds, which is found to be very sensitive to the flexibility and steric hindrance-of the imine ligands and very insensitive to electronic changes of the C-H bonds.