Double role of the hydroxy group of phosphoryl in palladium(II)-catalyzed ortho-olefination: a combined experimental and theoretical investigation.
Double role of the hydroxy group of phosphoryl in palladium(II)-catalyzed ortho-olefination: a combined experimental and theoretical investigation.
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DOI：
10.1021/jo402307x
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发表时间：
2014-01
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通讯作者：
L. Liu;Hang Yuan;T. Fu;Tao Wang;Xiang Gao;Z. Zeng;Jun Zhu;Yufen Zhao
中科院分区：
文献类型：
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作者：
L. Liu;Hang Yuan;T. Fu;Tao Wang;Xiang Gao;Z. Zeng;Jun Zhu;Yufen Zhao
用密度泛函理论计算了钯催化的磷酸基定向正烯化反应，探讨了甲基苯基膦酸氢酯和二甲基苯基膦酸酯反应性差异的原因。整个催化循环包括四个基本步骤：C-H键活化、金属转化、还原性消除和催化剂的回收，每个步骤都由不同的步骤组成。我们的计算表明，磷酸基的羟基几乎在所有步骤中都起着至关重要的作用，它不仅可以通过分子内氢键稳定中间体和过渡态，而且还可以作为质子供体，使η(1)- ch3coo（-）配体可以质子化形成易于去除的中性乙酸。这些发现解释了为什么只有苯基磷酸氢甲酯和苯基磷酸氢甲酯被发现是合适的反应伙伴。我们的机理发现进一步支持了用苯基膦酸甲氢催化pd催化邻烯烃的理论预测，并通过实验观察证实了期望的产物在中等产率下形成。
Density functional theory calculations have been carried out on Pd-catalyzed phosphoryl-directed ortho-olefination to probe the origin of the significant reactivity difference between methyl hydrogen benzylphosphonates and dimethyl benzylphosphonates. The overall catalytic cycle is found to include four basic steps: C-H bond activation, transmetalation, reductive elimination, and recycling of catalyst, each of which is constituted from different steps. Our calculations reveal that the hydroxy group of phosphoryl plays a crucial role almost in all steps, which can not only stabilize the intermediates and transition states by intramolecular hydrogen bonds but also act as a proton donor so that the η(1)-CH3COO(-) ligand could be protonated to form a neutral acetic acid for easy removal. These findings explain why only the methyl hydrogen benzylphosphonates and methyl hydrogen phenylphosphates were found to be suitable reaction partners. Our mechanistic findings are further supported by theoretical prediction of Pd-catalyzed ortho-olefination using methyl hydrogen phenylphosphonate, which is verified by experimental observations that the desired product was formed in a moderate yield.