过渡金属催化的C-C单键活化反应的机理研究与新反应发展

Due to the prevalence of C-C single bonds in organic compounds, the activation of C-C single bonds constitutes one task of basic and fundamental significance. However, it is often difficult to realize this task, which is attributed to the unfavorable thermodynamic and kinetic issues associated with the cleavage of C-C single bonds. In recent years, transition metal promoted C-C single bond activation reacions have received widespread attention and experienced great progress, but it is still at a very early stage for C-C activation reactions. There are still many challenges that should be met before C-C single bond activation reactions can be used for practical applications. The resolvement of these challenges is dependent on the understanding of the reaction mechanisms for these C-C activation processes. In this regard, quantum mechanical methods can play an effective role in that it allows for the ready access of many valuable information that are difficult or even impossible to obtain by conventional experimental means, such as the structures, energetics and reactivity of some key intermediates and detailed reaction pathways for some important elementary reactions for C-C activation. Unfortunately, up to now theoretical studies on C-C activation reactions are extremely scarce in the literature. In this context, a systematic theoretical study on the mechanisms for C-C activation is to be carried out in this project, aiming to promote the development of this important yet undeveloped area. The major concerns in this project include the evaluation of bond dissociation energies for typical M-C bonds, electronic structures and reactivity for some key intermediates proposed to be active during the process of C-C activation, the detailed mechanisms and electronic and ligands effects for some basic elementary reactions, and the elucidation of interesting mechanistic issues associated with some important catalytic C-C activation reactions, such as the selectivity problems and their origins. On the basis of these intensive studies, some experimental studies are to be envisaged to provide some evidence for the conclusions and hypotheses derived from theoretical studies, and to develop some more efficient and selective transition metal catalyzed C-C single bond activation reactions.

由于C-C单键在有机化合物中的普遍性，C-C单键的活化研究具有基础和重要的价值。但C-C单键活化时不利的热力学与动力学因素，导致C-C单键活化反应一般很困难。近年来，过渡金属促进的C-C单键活化反应得到了广泛的重视和较大的发展，但是仍然处于刚起步的阶段，有很多挑战和难题需要解决。这些问题的解决都依赖于对反应机理的深刻理解。量子力学计算的手段研究反应机理非常有用，能得到很多实验手段难以或无法得到的信息。目前这方面的文献报道非常少。本项目拟对过渡金属促进的C-C单键活化反应的机理进行一个较为系统和全面的理论研究，包括研究M-C键的键能，重要中间体的电子结构，一些重要基元反应的机理，以及一些催化的C-C活化反应中有意思的机理问题，如选择性及其根源等。在此基础上，结合一些必要的实验工作，对机理研究的结论和假设进行验证，为发展更加高效和选择性的过渡金属催化的C-C活化反应提供有价值的信息。

C-C单键的活化是有机化学的一个基本反应，但是由于C-C单键的键能一般较大，难以活化，导致高效的C-C单键活化反应的发展仍较为不足。本项目我们利用过渡金属的促进作用，发展了Pd和Cu催化的逆羟醛缩合类型的偶联反应和新型绿色安全的利用腈作为腈基来源的腈基化反应，系统地研究了各个反应因素对反应的影响，发展了较为高效的方法学条件，同时，对反应机理进行了较为深入的研究，我们的研究表明了逆羟醛缩合类型C-C键活化经历一个关键的椅式6元环过渡态结构，得到M-enolate类型的中间体化合物，它可以与卤代芳烃，醛、酮等亲电试剂偶联，得到各种产物。另外，我们对氧化条件下的C-C断裂机制的研究表明了腈类的断裂经历了了羰基腈的中间体，它们与金属铜发生羰基-CN的活化，得到Cu-CN关键活性中间体，它们可以与卤代芳烃，或芳基硼酸类进行偶联，从而实现了绿色安全的腈基化反应，反应以安全的有机腈作为腈基来源，这比传统上用剧毒的氰化物盐要绿色安全的多。这些研究探索发展了新的C-C断裂新反应，认识了新的活化机制，对有机化学具有基础的价值。