COMPARATIVE PHOTO-INDUCED OXIDATIVE ADDITION OF B-H, C-H, Si-H AND B-B BONDS

对反应机理的了解使化学家能够预测新反应的结果，并找出如何最有效地制造新化合物。含金属的过渡金属化合物，如Rh和Ru，被广泛用作有机和工业过程的催化剂。氧化加成反应形成了这类催化剂的一类众所周知的反应。本项目涉及的氧化加成反应有两个主要进展：(1)最简单的碳氢化合物(例如苯或戊烷)与硼化合物的催化反应的发展，这些反应可产生用于进一步反应的非常有用的产物；(2)认识到氧化加成反应有时通过称为sigma络合物的非经典中间体进行；例如，硅烷可能会与金属结合，而不会破坏中间sigma-络合物中的硅氢键，尽管它在产物中完全断裂。首先，在原理实验的证明中，我们已经证明了我们可以制备含有右旋配体的铑化合物。然后，我们可以获得氧化加成产品，其金属中心要么是右手的，要么是左手的，并可以监测这两种异构体的交换。这个交换过程告诉我们，存在具有镜面的中间体(或过渡态)。借助于理论和实验，我们可以推断Sigma复合体的存在。其次，这项建议通过使用短光脉冲来测量精心挑选的过渡金属化合物与硼化合物的反应速度，从而解决了硼的特殊之处。这些结果将借助与著名理论家艾森斯坦合作进行的理论计算来解释。第三，我们将使用核磁共振波谱来确定不同试剂组合竞争时的产品分布，例如允许硅和硼化合物竞争相同的过渡金属物种。最后，我们将研究被认为适合于连续两个氧化加成反应的过渡金属络合物。这些前体化合物在光的照射下发生反应，如果它们能用可见光而不是紫外光引发，在应用上将特别有趣。总体而言，这项研究将为我们提供可用于催化剂设计的不同类型的氧化加成反应之间的关系的详细图景。

A knowledge of reaction mechanisms is what enables chemists to predict the outcome of new reactions and work out how to make new compounds most effectively. Transition-metal compounds containing metals such as rhodium and ruthenium are used extensively as catalysts for organic and industrial processes. Oxidative addition reactions form a well-known class of reactions of such catalysts. There are two major developments in oxidative addition reactions that this project addresses: (1) the development of catalytic reactions of the simplest hydrocarbons (e.g. benzene or pentane) with boron compounds that yield very useful products for further reactions (2) the realisation that oxidative addition reactions sometimes proceed via non-classical intermediates called sigma complexes ; for instance, a silane may bind to the metal without breaking the silicon-hydrogen bond in the intermediate sigma-complex, although it is completely broken in the product. Firstly, in proof of principle experiments, we have demonstrated that we can make rhodium compounds that contain right-handed ligands. We can then obtain oxidative addition products that have metal centres that are either right-handed or left-handed and can monitor exchange of these two isomers. This exchange process tells us about the existence of intermediates (or transition states) with a mirror plane. With the help of theory and experiment we can infer the existence of sigma complexes. Secondly, this proposal addresses the question of what is special about boron by measuring the rates of reaction of carefully selected transition metal compounds with the boron compounds using a short light pulse to initiate the reactions. The results will be interpreted with the aid of theoretical calculations carried out in collaboration with Eisenstein, a well-known theorist. Thirdly, we will use NMR spectroscopy to determine the distribution of products when different combinations of reagents are in competition, for instance allowing silicon and boron compounds to compete for the same transition metal species. Finally, we will investigate transition metal complexes that are claimed to be suitable for two oxidative addition reactions in succession. These precursor complexes react on irradiation of light and it would be especially interesting for applications if they can be initiated with visible light rather than ultra-violet light. Overall, this study will give us a detailed picture of the relationships between different types of oxidative addition reactions that can be fed into catalyst design.