Synthesis and Electronic Structure of Bis(imino)pyridine Iron Metallacyclic Intermediates in Iron-Catalyzed Cyclization Reactions
Synthesis and Electronic Structure of Bis(imino)pyridine Iron Metallacyclic Intermediates in Iron-Catalyzed Cyclization Reactions
复制标题
DOI：
10.1021/ja400895j
复制
发表时间：
2013-03-27
影响因子：
15
通讯作者：
Chirik, Paul J.
中科院分区：
文献类型：
--
作者：
Hoyt, Jordan M.;Sylvester, Kevin T.;Chirik, Paul J.
双（亚氨基）吡啶铁二氮化合物（（PDI）-P-iPr（TB））Fe（N-2）（2）（（iPr（TB））PDI = 2，6-（2，6-Pr-i（2）-C6 H3- N=C中心点（CH 2）（3））（2）（C5 H1 N））是二烯丙基胺的[2 pi + 2 pi]环加成以及N-甲苯磺酰基化烯炔和二炔的加氢环化的有效预催化剂。将化学计量量的氨基取代的烯炔和二炔底物添加到（（PDI）-P-iPr（TB））Fe（N-2）（2）中导致分离出催化活性的双（亚氨基）吡啶铁金属乳糖中间体。磁化学、X射线衍射、穆斯堡尔谱学和计算研究的结合建立了S = 1的铁化合物，其最好描述为与螯合自由基阴离子（S-PDI = 1/2）反铁磁性耦合的中间自旋铁（III）（S-Fe = 3/2）。与[2 pi + 2 pi]环加成反应有关的催化活性的双（亚氨基）吡啶铁二烯和金属杂环也被分离和结构表征。结合的磁性，结构，光谱和计算数据支持Fe（I）Fe（III）催化循环，其中双（亚氨基）吡啶螯合物保持其单电子还原自由基阴离子形式。这些研究修订了以前的机制建议，专门涉及亚铁中间体，并强调氧化还原活性的双（亚氨基）吡啶螯合物，使催化环化化学与铁的重要性。
The bis(imino)pyridine iron dinitrogen compound, ((PDI)-P-iPr(TB))Fe(N-2)(2) ((iPr(TB)) PDI = 2,6-(2,6-Pr-i(2)-C6H3- N=C center dot(CH2)(3))(2)(C5H1N)) is an effective precatalyst for the [2 pi + 2 pi] cycloaddition of diallyl amines as well as the hydrogenative cyclization of N-tosylated enynes and diynes. Addition of stoichiometric quantities of amino-substituted enyne and diyne substrates to ((PDI)-P-iPr(TB))Fe(N-2)(2) resulted in isolation of catalytically competent bis(imino)pyridine iron metallacycle intermediates. A combination of magnetochemistry, X-ray diffraction, and Mossbauer spectroscopic and computational studies established S = 1 iron compounds that are best described as intermediate-spin iron(III) (S-Fe = 3/2) antiferromagnetically coupled to a chelate radical anion (S-PDI = 1/2). Catalytically competent bis(imino)pyridine iron diene and metallacycles relevant to the [2 pi + 2 pi] cycloaddition were also isolated and structurally characterized. The combined magnetic, structural, spectroscopic, and computational data support an Fe(I) Fe(III) catalytic cycle where the bis(imino)pyridine chelate remains in its one-electron reduced radical anion form. These studies revise a previous mechanistic proposal involving exclusively ferrous intermediates and highlight the importance of the redox-active bis(imino)pyridine chelate for enabling catalytic cyclization chemistry with iron.