水相中TiO2光催化活化C-H键选择性脱饱和反应

In this proposal, TiO2 photocatalyst will be used to activate several kinds of typical C-H bonds with the purpose of performing selective desaturation (dehydrogenation) in aqueous medium by using oxygen in air and completing three important transformations of carbonylation (C=O), enamination (=N-) and alkenation (C=C) in mild conditions. The emphasis in this proposal is on determining the controlled parameters of selective transformation by using oxygen as final H and electron receptor in the conduction band of TiO2 photocatalyst, and what's more, seeking a band-band modified method to avoid oxygen forming active oxygen and secondary carbon-centered radicals. Especially, when water is used as the sole solvent, two methods will be performed to prevent the non-selective hydroxyl radicals formed by holes in the H2O oxidation to destroy the selectivity of the whole reaction. On one hand, nonmetal-doped TiO2 photocatalyst activated by visible light will be applied to decrease the oxidation potential of valence band; on the other hand, by modifying the crystalline pattern and faces of TiO2, H2O can occupy the crystalline faces in the form of molecules instead of dissociate OH in order to achieve the preferential oxidation of substrate in valence band. The object of this proposal is to examine the structure-activity relationship of selectively photocatalytic dehydrogenation and exposed structure on the surface of photocatalyst and to accomplish three important environment-friendly and selective desaturation reactions with the solvent of H2O and O2 receptor for electrons and H.

本项目尝试在温和条件下，利用TiO2光催化活化几类典型的C-H键，实现利用空气中的氧在水相介质中进行具有选择性的脱饱和（脱H）反应，拟完成三类重要的羰基化（C=O）、烯胺化（=N-）和烯烃化（C=C）转化反应。重点考察O2作为最终的H受体和电子受体在TiO2光催化剂的导带实现选择性转移的控制因素，寻找避免O2产生活性氧和次级的碳中心自由基产生的TiO2带-带调控方法。特别是在水为唯一溶剂的情况下，拟通过两种措施避免价带空穴氧化H2O产生无选择性的OH自由基破坏整个转化反应的选择性，一是通过可见光激发掺杂非金属元素的TiO2光催化剂降低价带氧化电位，二是调控TiO2的晶型、晶面实现调节H2O以分子形式而非解离OH形式占据晶面，实现底物在价带的优先氧化。观察选择性催化脱H反应和催化剂表面暴露结构的构效关系，完成H2O为溶剂、O2为最终电子和H受体的三类重要的绿色、选择性的脱饱和反应。

项目研究进展顺利，按计划任务书完成了各项任务指标，实现了光催化活化烷烃C-H键制醛酮、光催化氧化脂肪醇制醛酮、光催化环氧化合物脱氧制烯烃、光催化氧化胺类化合物制亚胺等重要有机转化反应，揭示了环氧化合物脱氧反应中的协同双电子转移过程等相关反应机理，为实现有机分子在温和条件下、高效、高选择性的转化反应提供了新的思路和方法，为利用太阳能实现绿色有机合成反应提供了可能。在Acc. Chem. Res.、Angew. Ed. Chem. Int.、Chem. Commun.、Chem. - Eur. J.等国际SCI期刊上发表相关论文7篇。