Visible-Light-Induced Selective Photocatalytic Aerobic Oxidation of Amines into Imines on TiO2
Visible-Light-Induced Selective Photocatalytic Aerobic Oxidation of Amines into Imines on TiO2
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可见光诱导 TiO2 上胺选择性光催化有氧氧化成亚胺
DOI：
10.1002/chem.201102779
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发表时间：
2012-02-01
影响因子：
4.3
通讯作者：
Zhao, Jincai
中科院分区：
文献类型：
--
作者：
Lang, Xianjun;Ma, Wanhong;Zhao, Jincai
亚胺是合成精细化学品、医药、农用化学品的重要中间体。用分子氧将胺选择性氧化成相应的亚胺是最基本的化学转化之一。在此，我们报道了在可见光照射（λ>420 nm）下，以大气分子氧为氧化剂，在锐钛矿型TiO2 表面上将一系列苄胺氧化成相应的亚胺。该系统的可见光响应是由二氧化钛表面吸附苄胺形成表面络合物引起的。通过对专门设计的苄胺产物的分析，我们证明了通过氧转移机制进行高选择性氧化反应，得到相应的羰基化合物，其与胺进一步缩合将生成最终的亚胺产物。我们发现，当选择伯苄胺（13 个例子）作为底物时，亚胺产物的选择性达到中等至优异（约 3894%），转化率中等至优异（约 4495%）。当选择仲苄胺（15个例子）作为底物时，相应的亚胺和醛均被检测为主要产物，具有中等到高的转化率（约18100％）和较低的亚胺产物选择性（约1469％）。当选择三苄胺作为底物时，以50％的转化率得到亚胺(27％)、二苄胺(24％)和苯甲醛产物(39％)。该报告可以被视为一个原型系统，用于激活与N、O和S原子等杂原子相邻的C?H键，并使用TiO2作为光催化剂在可见光照射下以空气或分子氧作为末端氧化剂进行氧化官能化。
Imines are important intermediates for the synthesis of fine chemicals, pharmaceuticals, and agricultural chemicals. Selective oxidation of amines into their corresponding imines with dioxygen is one of the most-fundamental chemical transformations. Herein, we report the oxidation of a series of benzylic amines into their corresponding imines with atmospheric dioxygen as the oxidant on a surface of anatase TiO2 under visible-light irradiation (?>420 nm). The visible-light response of this system was caused by the formation of a surface complex through the adsorption of a benzylic amine onto the surface of TiO2. From the analysis of products of specially designed benzylic amines, we demonstrated that a highly selective oxygenation reaction proceeds via an oxygen-transfer mechanism to afford the corresponding carbonyl compound, whose further condensation with an amine would generate the final imine product. We found that when primary benzylic amines (13 examples), were chosen as the substrates, moderate to excellent selectivities for the imine products were achieved (ca. 3894?%) in moderate to excellent conversion rates (ca. 4495?%). When secondary benzylic amines (15 examples) were chosen as the substrates, both the corresponding imines and aldehydes were detected as the main products with moderate to high conversion rates (ca. 18100?%) and lower selectivities for the imine products (ca. 1469?%). When tribenzylamine was chosen as the substrate, imine (27?%), dibenzylamine (24?%), and benzaldehyde products (39?%) were obtained in a conversion of 50?%. This report can be viewed as a prototypical system for the activation of C?H bonds adjacent to heteroatoms such as N, O, and S atoms, and oxofuctionalization with air or dioxygen as the terminal oxidant under visible-light irradiation using TiO2 as the photocatalyst.