<br>甲酰化或甲基化：什么决定了 1,3,2-二氮杂磷烯催化的胺、CO2 和氢硅烷反应的化学选择性？,Chemical Science

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甲酰化或甲基化：什么决定了 1,3,2-二氮杂磷烯催化的胺、CO2 和氢硅烷反应的化学选择性？
Chemical Science ( IF 7.6 ) Pub Date : 2017-09-11 00:00:00 , DOI: 10.1039/c7sc00824d
Yu Lu ₁ , Zhong-Hua Gao ₂ , Xiang-Yu Chen ₂ , Jiandong Guo ₁ , Zheyuan Liu ₁ , Yanfeng Dang ₁ , Song Ye ₂ , Zhi-Xiang Wang ₁

Affiliation

进行 DFT 计算是为了深入了解胺（例如甲基苯胺 (1a)/2,2,4,4,-四甲基哌啶 (2a)）与 CO2 和氢硅烷 ([Si]H2, [Si] 的甲酰化/甲基化机制。 ]=Ph2Si)，由 1,3,2-二氮杂磷烯 ([NHP]H) 催化。与一般提出的用CO2进行胺甲基化的顺序机制（即甲基化通过甲酰化进行，然后进一步还原甲酰胺得到N-甲基化胺）不同，该研究表征了甲酰化和甲基化之间的竞争机制。化学选择性源于胺和[NHP]H氢化物之间竞争攻击[Si](OCHO)2（CO2插入[Si]H2的产物）的甲酰氧基碳。当胺（例如1a）的攻击获胜时，转化产生甲酰胺（1b），否则（例如2a）会产生N-甲基化胺（2c）。 [Si]H2 或 [NHP]H 对甲酰胺的还原在动力学上是非常不利的，因此我们呼吁关注用于理解胺与 CO2 甲基化的顺序机制。此外，该研究还有以下关键机制发现。 [NHP]H 对 CO2 的活化建立了平衡：[NHP]H + CO2 ⇄ [NHP]OCHO ⇄ [NHP]+ + HCO2-。这些离子发挥催化作用，通过 HCO2- 促进甲酰化，或通过 [NHP]+ 促进甲基化。在1a甲酰化中，HCO2-引发反应，产生1b和硅烷醇副产物。然而，引发后，作为氢转移梭的硅烷醇副产物比 HCO2- 更有效地促进甲酰化。在 2a 甲基化中，[NHP]+ 促进关键物质、甲醛和碳正离子 (IM17+) 的产生。我们的实验研究证实了我们的计算机制。

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Formylation or methylation: what determine the chemoselectivity of reactions of amine, CO2, and hydrosilane, catalyzed by 1,3,2-diazaphospholene?

DFT computations have been performed to gain insight into the mechanisms of formylation/methylation of amines (e.g. methylaniline(1a)/2,2,4,4,-tetramethylpiperidine (2a)) with CO2 and hydrosilane ([Si]H2, [Si]=Ph2Si), catalyzed by 1,3,2-diazaphospholene ([NHP]H). Different from the generally proposed sequential mechanism for methylation of amine with CO2, i.e. methylation proceeds via formylation, followed by further reduction of formamide to give N-methylated amine, the study characterized a competition mechanism between formylation and methylation. The chemoselectivity originates from the competition between amine and [NHP]H hydride to attack formyloxy carbon of [Si](OCHO)2 (the insertion product of CO2 into [Si]H2). When the attack of an amine (e.g. 1a) wins, the transformation affords formamide (1b) and would otherwise (e.g. 2a) result in N-methylated amine (2c). The reduction of formamide by [Si]H2 or [NHP]H is highly unfavorable kinetically, thus we call attention to the sequential mechanism for understanding methylation of amine with CO2. In addition, the study has the following key mechanistic findings. The activation of CO2 by [NHP]H establishes an equilibrium: [NHP]H + CO2 ⇄ [NHP]OCHO ⇄ [NHP]+ + HCO2-. The ions play catalytic roles to promote formylation via HCO2- or methylation via [NHP]+. In 1a formylation, HCO2- initiates the reaction, giving 1b and silanol byproducts. However, after the initiation, silanol byproducts acting as hydrogen transfer shuttles are more effective than HCO2- to promote the formylation. In 2a methylation, [NHP]+ promotes the generations of the key species, formaldehyde and a carbocation species (IM17+). Our experimental study corroborates our computed mechanisms.

更新日期：2017-09-11

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