Titania-Supported Iridium Subnanoclusters as an Efficient Heterogeneous Catalyst for Direct Synthesis of Quinolines from Nitroarenes and Aliphatic Alcohols
Titania-Supported Iridium Subnanoclusters as an Efficient Heterogeneous Catalyst for Direct Synthesis of Quinolines from Nitroarenes and Aliphatic Alcohols
复制标题
二氧化钛负载的铱亚纳米团簇作为高效多相催化剂，用于硝基芳烃和脂肪醇直接合成喹啉
DOI：
10.1002/anie.201104089
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发表时间：
2011-01-01
影响因子：
16.6
通讯作者：
Fan, Kang-Nian
中科院分区：
文献类型：
--
作者：
He, Lin;Wang, Jian-Qiang;Fan, Kang-Nian
近年来，金属纳米颗粒(NPs)或纳米簇(NCs)作为多功能催化剂用于绿色可持续有机合成，由于其独特的性质，如大的比表面积和可调的形状，近年来引起了极大的兴趣。[1]控制它们的大小、形状、分散性，特别是金属NPs/NCs与特定的多相载体的结合对于在期望的应用中提高活性和选择性是必不可少的。[2]尽管在许多经典的转化中，可重复使用的负载型金属NPs/NCS表现出远远优于传统金属络合物催化剂的性能，[3]金属NPs/NCs提供的可持续串联催化的可能性几乎没有被探索过，它允许通过一锅多步反应迅速增加分子的复杂性。[4]这种情况有些令人惊讶，因为综合使用由金属NPs/NCS产生的反应中心和合适的载体可以成为设计多任务催化剂的有力手段，因此为以多米诺骨牌方式从简单和方便的底物合成复杂的分子靶标提供了有前途的候选方案。[6]喹啉及其衍生物是一类重要的生物活性化合物，被指定为抗疟疾、抗细菌、抗高血压、此外，喹啉类化合物是用于制备纳米结构和聚合物的有价值的合成物，这些纳米结构和聚合物将增强的电子、光电或非线性光学性能与优异的机械性能结合在一起。[8]制备功能化喹啉类化合物最常见的方法包括几个命名反应，如Skraup、[9]Doebner-Von Miller、[10]Conrad-Limpach、[11]Friedländer、[12]和Pfitzinger[13]。尽管这些方法很实用，但它们往往需要昂贵的芳香胺和不稳定的羰基化合物，恶劣的条件，以及大量危险的酸或碱的使用。更大的问题是，复杂的取代胺本身必须首先合成，主要是通过多步过程。[15]开发新的策略来快速、清洁和有效地获得喹啉类化合物一直是相当努力的重点。[16]在这种情况下，通过一锅串联反应直接从现成的硝基芳烃和脂肪醇中组装喹啉类化合物是非常有吸引力的。[17]不幸的是，这种直接的方法被证明是极其困难的，有效的催化剂体系受到严重限制。到目前为止，只有两个均相过渡金属催化体系[17a，b]和一个紫外光催化体系[17c]被报道。从综合和经济的角度来看，这些系统没有实际用途，因为存在不可重复使用的固有问题，需要对外部光源进行特殊处理，或者条件恶劣，以及产量低和衬底范围有限。在这里，我们首次报道了一种新的多任务催化剂，该催化剂能够在温和的条件下，通过一种简单的顺序转移还原-缩合-脱氢途径，促进由硝基芳烃和醇快速直接生成有价值的喹啉。亚纳米Ir团簇与具有适当表面酸性的氧化物载体(例如，二氧化钛)的组合提供了最佳催化剂。之所以选择Ir，是因为Ir纳米粒子及其配合物能够催化包括…在内的多种有机转化。
The use of metal nanoparticles (NPs) or nanoclusters (NCs) as versatile catalysts for green and sustainable organic synthesis has attracted tremendous interest in recent years owing to their unique properties, such as a large surface-tovolume ratio and tunable shapes.[1] The control of their size, shape, dispersity, and in particular the combination of metal NPs/NCs with a specific heterogeneous support is essential for enhanced activity and selectivity in a desired application.[2] Although in many classical transformations, reusable supported metal NPs/NCs have exhibited far superior performance than those of conventional metal complex catalysts,[3] the possibilities offered by metal NPs/NCs for sustainable tandem catalysis that allows a rapid increase in molecular complexity through one-pot multistep reactions have scarcely been explored.[4] This situation is somewhat surprising since the integrated use of the reactive sites generated from metal NPs/NCs and a suitable support could be a powerful means for the design of multitask catalysts,[5] thus providing promising candidates to perform sophisticated tandem reactions for synthesis of complex molecular targets from simple and convenient substrates in a domino fashion.[6] Quinolines and their derivatives are an important class of bioactive compounds that are prescribed as antimalarial, antibacterial, antihypertensive, and antiinflammatory drugs.[7] In addition, quinolines are valuable synthons used for the preparation of nanostructures and polymers that combine enhanced electronic, optoelectronic, or nonlinear optical properties with excellent mechanical properties.[8] The most frequent routes to prepare functionalized quinolines include several named reactions, such as Skraup,[9] Doebner–Von Miller,[10] Conrad–Limpach,[11] Friedländer,[12] and Pfitzinger [13] syntheses based on the reaction of substituted anilines with carbonyl compounds. Despite their utility, these methods often suffer from the requirement of costly aromatic amines and unstable carbonyl compounds, harsh conditions, and the use of large amounts of hazardous acids or bases.[14] More problematic is that the complicated substituted amines must themselves be synthesized first, mostly by multistep procedures.[15] The development of new strategies to obtain quinolines in a fast, clean, and efficient way has been the focus of considerable efforts.[16] In this context, the assembly of the quinolines directly from readily available nitroarenes and aliphatic alcohols through a one-pot tandem reaction is highly attractive.[17] Unfortunately, this straightforward method has proven to be extremely difficult, and effective catalyst systems were severely limited. To date, only two homogeneous transition-metal catalytic systems [17a, b] and one UV-irradiated photocatalytic system [17c] have been reported. From a synthetic and economic point of view, these systems are not practically useful because of the inherent problems of non-reusability, the necessity of special handling of an external light source, or harsh conditions, as well as low yields and limited substrate scope. Herein, we report for the first time that a new heterogeneous iridium-based multitask catalyst facilitates the rapid direct construction of valuable quinolines from nitroarenes and alcohols under mild conditions through a facile sequential transfer reduction–condensation–dehydrogenation pathway. The combination of sub-nanosized iridium clusters with an oxide support possessing suitable surface acidity, for example, TiO2, provides an optimal catalyst. Iridium was selected because Ir NPs and complexes are well known to catalyze a wide range of organic transformations including …