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Dehydrogenative synthesis of benzimidazoles under mild conditions with supported iridium catalysts

机译：Dehydrogenative合成苯并咪唑温和的条件和支持铱催化剂

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摘要

Solid supported iridium catalysts, which show excellent activity for the dehydrogenative synthesis of benzimidazoles from primary alcohols and phenylenediamine derivatives under mild reaction conditions, were developed. Among the catalysts examined, the titania-supported iridium catalyst showed the highest activity, and benzimidazole derivatives were selectively produced at temperatures of 80 degrees C or higher. For example, the reaction of phenylenediamine (1a) with benzyl alcohol (2a) in the presence of Ir(1.0 wt%)/TiO2 (1.0 mol%, towards 1a) at 120 degrees C selectively gave 2-phenylbenzimidazole (3aa) in 80% yield after 6 h and over 90% yield after 18 h. A high turnover number (TON) of more than 800 was achieved in the reaction at a higher substrate-to-catalyst ratio. Reduction of the catalysts under a hydrogen atmosphere at around 500 to 600 degrees C is essential for their significant activity. Characterization of the catalysts by gas adsorption, XRD, XPS, H-2-TPR, TEM, and XAFS techniques revealed that highly-dispersed nanoparticles of the iridium(0) species (ca. 1 to 2 nm in diameter) formed on TiO2 are responsible for the catalysis. The catalysts could be recycled without a significant loss of activity, and the leaching of the iridium species into the solution during the catalytic runs was negligible, which suggests that the present catalysts would be excellent from both environmental and practical perspectives.
机译：固体支持铱催化剂,这节目dehydrogenative优秀的活动苯并咪唑的合成主要醇和苯二胺衍生品在温和反应条件,开发。titania-supported铱催化剂的研究催化剂表现出最高的活动,苯并咪唑衍生物选择性在80摄氏度的高温或生产更高。苯二胺与苯甲醇(1)(2)红外光谱的存在(1.0 wt %) /二氧化钛(1.0摩尔%,对1)在120摄氏度有选择地给2-phenylbenzimidazole (3 aa)在80%的收益率618 h后h和超过90%的收益率。高营业额数量(吨)超过800中实现反应在较高substrate-to-catalyst比率。降低催化剂的氢气氛在500到600摄氏度左右必不可少的重要活动。催化剂的表征气体吸附、XRD、XPS、H-2-TPR TEM和XAFS技术显示,高度分散的纳米粒子的铱(0)物种(ca。1直径2 nm)上形成二氧化钛是负责任的催化。回收没有重大损失的活动,和铱物种的浸出在催化应用解决方案可以忽略不计,这表明现在从两个催化剂将是优秀的环境和实际的观点。

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