Pd(OAc)2-catalyzed C-H activation/C-O cyclization: mechanism, role of oxidant-probed by density functional theory.
Pd(OAc)2-catalyzed C-H activation/C-O cyclization: mechanism, role of oxidant-probed by density functional theory.
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DOI：
10.1021/jo4010712
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发表时间：
2013-08
期刊：
影响因子：
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通讯作者：
Bing Lian;Lei Zhang;G. Chass;D. Fang
中科院分区：
文献类型：
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作者：
Bing Lian;Lei Zhang;G. Chass;D. Fang
采用密度泛函理论研究了Pd（OAc）2催化的苯基叔丁醇在全氟苯（C6 F6）溶剂中的C-H键活化及随后的分子内C-O键偶联反应.完整的，非截断模型的真实的化学转变进行了研究，与最近的X射线测定的结构一致。构象分析提供了所用几何结构的热力学有效性。比较了B3 LYP/DZVP和B3 LYP/BS 1方法（BS 1 = TZVP（H，C，O）+ SDD（Pd，I）），采用IDSCRF方法计算了C6 F6溶剂的贡献，通过内禀反应坐标确定了关键过渡态。提出的反应机理分为C-H活化、氧化、还原消除、催化剂回收四步。定量比较了两种竞争性反应途径，Pd的氧化态不同（+2 vs +4）。结果表明，涉及Pd（IV）中间体的途径比Pd（II）途径更自发，因此更有可能，后者受到动力学上难以实现的还原消除步骤的阻碍，总能量和自由能垒分别为41.0和38.6 kcal. mol（-1）。氧化剂和Pd（IV）物种所扮演的角色也通过Bader的原子在分子波函数分析得到了解决，为C-H活化化学提供了定量的电子度量。
A series of density functional theory determinations have been carried out to characterize Pd(OAc)2-catalyzed C-H activation and subsequent intramolecular C-O bond-coupling of phenyl-tert-butanol in perfluorobenzene (C6F6) solvent. Full, nontruncated models of the real chemical transformations were studied, with structures in agreement with recent X-ray determinations. Conformational analyses have provided thermodynamic validity of the geometric structures used. The B3LYP/DZVP and B3LYP/BS1 methods (BS1 = TZVP(H,C,O) + SDD(Pd,I)) were comparatively employed, with C6F6 solvent contributions accounted for by the IDSCRF method; key transition states were confirmed by intrinsic reaction coordinate determinations. The novel reaction mechanism proposed was divided into the following four steps: C-H activation, oxidation, reductive elimination, catalyst recovery. Two competing reaction routes were quantitatively compared, differing in the oxidation state of Pd (+2 vs +4). Results reveal the pathway involving Pd(IV) intermediates to be more spontaneous and, therefore, more probable than the Pd(II) path, the latter hindered by a kinetically inaccessible reductive elimination step, with total energy and free energy barriers of 41.0 and 38.6 kcal·mol(-1), respectively. The roles played by the oxidant and Pd(IV) species have also been addressed through Bader's atoms-in-molecules wave function analyses, providing a quantitative electronic metric for C-H activation chemistry.