Synthetic, structural, and mechanistic studies on the oxidative addition of aromatic chlorides to a palladium (N-heterocyclic carbene) complex:: Relevance to catalytic amination
Synthetic, structural, and mechanistic studies on the oxidative addition of aromatic chlorides to a palladium (N-heterocyclic carbene) complex:: Relevance to catalytic amination
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DOI：
10.1021/ja035565k
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发表时间：
2003-08-20
影响因子：
15
通讯作者：
Leonard, J
中科院分区：
文献类型：
--
作者：
Lewis, AKD;Caddick, S;Leonard, J
氧化加成产物trans-[Pd(NHC)(2)(Ar)Cl] (NHC =环- c {(NBuCH)- bu - i}(2)；Ar = Me-4-C6H4, MeO-4-C6H4, CO2Me-4-C6H4)从ArCl与胺化预催化剂[Pd(NHC)(2)]的反应中得到了较好的收率，并进行了结构表征。当Ar = Me-4-C6H4时，Pd-NHC的解离焓为25.57 kcal mol（-1）。详细的动力学研究表明，氧化加成反应是通过解离机制进行的。Me-4-C6H4Cl氧化加成[Pd(NHC)(2)]的速率数据与[Pd(NHC)(2)]催化啉与4-氯甲苯偶联的速率数据相比较，与催化胺化反应中的速率决定氧化加成一致。三种芳基氯化物与[Pd(NHC)(2)] （CO2Me-4-C6H4Cl > Me-4-C6H4Cl > MeO-4-C6H4Cl）的相对氧化加成速率反映了取代基的电子性质，也反映了这些芳基卤化物在胺化反应中偶联效率的平行趋势。
The oxidative addition products trans-[Pd(NHC)(2)(Ar)Cl] (NHC = cyclo-C{(NBuCH)-Bu-I}(2); Ar = Me-4-C6H4, MeO-4-C6H4, CO2Me-4-C6H4) have been isolated in good yields from the reactions of ArCl with the amination precatalyst [Pd(NHC)(2)] and structurally characterized. The former undergo reversible dissociation of one NHC ligand at elevated temperatures, and a value of 25.57 kcal mol(-1) has been determined for the Pd-NHC dissociation enthalpy in the case where Ar = Me-4-C6H4. Detailed kinetic studies have established that the oxidative addition reactions proceed by a dissociative mechanism. Rate data for the oxidation addition of Me-4-C6H4Cl to [Pd(NHC)(2)] compared to that obtained for the [Pd(NHC)(2)]-catalyzed coupling of morpholine with 4-chlorotoluene are consistent with a rate-determining oxidative addition in the catalytic amination reaction. The relative rates of oxidative addition of the three aryl chlorides to [Pd(NHC)(2)] (CO2Me-4-C6H4Cl > Me-4-C6H4Cl > MeO-4-C6H4Cl) reflect the electronic nature of the substituents and also parallel observed trends in coupling efficiency for these aryl halides in aminations.