A Modified Cationic Mechanism for PdCl2-Catalyzed Transformation of a Homoallylic Alcohol to an Allyl Ether,Organometallics

当前位置： X-MOL 学术 › Organometallics › 论文详情

Our official English website, www.x-mol.net, welcomes your feedback! (Note: you will need to create a separate account there.)

A Modified Cationic Mechanism for PdCl2-Catalyzed Transformation of a Homoallylic Alcohol to an Allyl Ether
Organometallics ( IF 2.5 ) Pub Date : 2019-07-31 , DOI: 10.1021/acs.organomet.9b00276
Kaveh Farshadfar ₁ , Antony Chipman ₂ , Mahdieh Hosseini ₁ , Brian F. Yates ₂ , Alireza Ariafard _{1,

2}

Affiliation

Density functional theory calculations were utilized to investigate a PdCl₂-catalyzed transformation involving double-bond migration (alkene isomerization), followed by condensation with methanol starting from a homoallylic alcohol. Against the proposed mechanism in the literature [Tan, J.; Org. Biomol. Chem. 2008, 6, 1344−1348], which assumes involvement of Pd^IV intermediates for both double-bond migration and condensation, our calculations preclude this supposition. The double-bond migration process is found to proceed through the cationic mechanism, accessed by the increased acidity of the allylic hydrogen in the Pd-activated alkene. The cationic mechanism commences with allylic C–H bond deprotonation by MeOH (solvent), giving an η¹-allyl complex which then rearranges through an η³- to another η¹-allyl complex, followed by protodemetalation. The allyl rearrangement was identified as an essential step in order for the double-bond migration to proceed via a lower activation energy. This double-bond migration mechanism which does not involve a Pd^IV intermediate is similar to the one reported earlier [Senan, A. M.; ACS Catal. 2016, 6, 4144−4148]. Once double-bond migration is completed, nucleophilic attack of MeOH to the Pd^II-activated new double bond initiates the condensation reaction. The nucleophilic attack transition structure gains some stability from a hydrogen bond between the entering alcohol and the available hydroxyl group at the allylic position of the isomerized substrate. In the final step of condensation, the hydroxyl abstracts the proton from the carbon-bonded MeOH to give an allyl ether product and a free water. The findings of this paper are anticipated to add value in the areas of the alkene isomerization and condensation processes involving transition metal complexes as catalysts.

中文翻译：

PdCl 2催化均烯丙基醇转化为烯丙基醚的改性阳离子机理

利用密度泛函理论计算来研究PdCl ₂催化的转化，该转化涉及双键迁移（烯烃异构化），然后与甲醇从均烯丙基醇中缩合。反对文献中提出的机制[谭J.; 单位生物分子。化学 2008，6，1344年至1348年]，其中假定的Pd参与^IV为双键迁移和缩合两个中间体，我们的计算排除这一假设。发现双键迁移过程是通过阳离子机理进行的，该机理通过Pd活化烯烃中烯丙基氢的酸度增加而获得。与烯丙基C-H键去质子化的阳离子机制启动用MeOH（溶剂），得到的η ¹ -烯丙基配合物，其然后通过重排η ³ -到另一个η ¹-烯丙基复合物，然后进行原金属脱金属。烯丙基重排被认为是必不可少的步骤，以便通过较低的活化能进行双键迁移。这种不涉及Pd ^IV中间体的双键迁移机制与之前报道的类似[上午塞南; ACS Catal。 2016，6，4144-4148]。一旦双键迁移完成，MeOH对Pd ^II活化的新双键的亲核攻击将引发缩合反应。亲核进攻转变结构从进入的醇与异构化底物的烯丙基位置处的可用羟基之间的氢键获得一定的稳定性。在缩合的最后步骤中，羟基从碳键合的MeOH中抽出质子，得到烯丙基醚产物和游离水。预期本文的发现将在涉及过渡金属络合物作为催化剂的烯烃异构化和缩合过程领域中增加价值。

更新日期：2019-08-01

点击分享查看原文

点击收藏

阅读更多本刊新发论文本刊介绍/投稿指南