Asymmetric Catalysis with Alkaline Earth Metals: Towards Greener Chemical Processes

催化剂在化学过程中扮演着重要的角色，无论是在学术研究中还是在世界范围内的工业舞台上。催化剂不会被化学反应消耗，而是通过降低反应进行所需的能量来发挥作用，从而降低反应温度，同时提高反应的选择性。在许多情况下，没有催化剂化学反应是不可能的。因此，催化剂是绿色化学过程的重要组成部分，它提高了反应效率，并使新物质得以制备。催化剂在商业化工生产中无处不在；大约80%的原料化学品都是使用催化剂生产的。许多催化剂都是以昂贵的稀有金属为基础的，使用稀有金属会带来一些问题。由于它们的稀有性，按照目前的消耗速度，到本世纪末，许多此类金属的开采将变得不经济。在短期内，与使用这些金属相关的采矿和回收成本是巨大的，可能是令人望而却步的。这项提议旨在利用廉价和环境友好的第二族金属，特别是钙，作为解决这一问题的潜在解决方案，开发不对称催化这一新兴领域。第二族金属最近显示出很大的前景，在催化中的应用显示了它们在这一领域的潜力。因此，随着化学家寻求开发新的新兴技术，使现有的化学过程更加清洁，同时降低成本，第2族金属将为绿色催化做出重大贡献。与第二族金属相关的主要限制之一是明确定义的分子物种在溶液中的稳定性；这有使络合物在催化中不活性或非选择性的趋势。在制备稳定的络合物方面，非立体选择性体系最近有了重要的进展。因此，我们的主要目标是推动第二族金属的催化应用超越目前的水平，进入不对称催化的领域。为此，我们将开发一系列手性支撑配体，旨在提高第二族金属配合物的稳定性。这样形成的络合物将使立体定向性质也能够被控制，以及独立地控制配体结合强度，从而可以在不影响催化活性的情况下找到最佳结合强度。2族化合物的配位化学和反应性将被研究，以评估它们的稳定性，以及它们对与催化反应有关的不饱和底物的反应活性。本建议中描述的催化应用将集中在不对称氢胺化反应，这是一种100%原子效率的合成路线，可获得大量有机产品和中间体。如果催化剂能够实现对反应产物的立体控制，这将为使用第2族金属的不对称催化的进一步发展打开大门，向更清洁和廉价的催化工艺又迈进了一步。

Catalysts play an important role in chemical processes, both in academic research and on the worldwide industrial stage. Catalysts are not consumed by chemical reactions, but act by reducing the energy required for a reaction to proceed, thus reducing the reaction temperature, whilst at the same time increasing the selectivity of the reaction. In many cases chemical reactions are not possible without a catalyst. Catalysts are therefore an essential component of green chemical processes, increasing the efficiency of reactions and enabling new substances to be prepared. Catalysts are ubiquitous in commercial chemical production; with some 80% of feedstock chemicals produced using a catalyst. Many of the catalysts are based upon expensive rare metals, the use of which presents a number of problems. By virtue of their rarity, at the current rate of consumption many of these metals will become uneconomical to mine by the end of this century. In the short term, the mining and recycling costs associated with using these metals are significant, and can be prohibitive. This proposal aims to develop the emerging area of asymmetric catalysis using the inexpensive and environmentally benign Group 2 metals, particularly calcium, as a potential solution to this problem.Group 2 metals have shown much recent promise, with applications in catalysis showing their potential in this area. The Group 2 metals are therefore poised to make a significant contribution to Green Catalysis , as chemists seek to develop new and emerging technologies to render existing chemical processes cleaner whilst reducing costs. One of the main limitations associated with Group 2 metals is the stability of well-defined molecular species in solution; this has the tendency of rendering complexes either inactive or non-selective in catalysis. There have been important recent developments with non-stereoselective systems regarding the preparation of stable complexes. Our main objective is therefore to advance the catalytic applications of Group 2 metals beyond their current level, and into the arena of asymmetric catalysis.To this end, a series of chiral supporting ligands will be developed which are designed to increase the stability of Group 2 metal complexes. The complexes thus formed will enable the stereodirecting properties to be controlled as well independently controlling the ligand binding strength, such that an optimum binding strength can be found without compromising on catalytic activity. The coordination chemistry and reactivity of Group 2 complexes will be studies in order to assess their stability, and their reactivity towards unsaturated substrates which are pertinent to catalytic reactions.The catalytic applications described in this proposal will concentrate on the asymmetric hydroamination reaction, a 100% atom efficient synthetic route to a plethora of organic products and intermediates. Should the catalysts enable stereocontrol over the reaction products, this will open the door for further developments in asymmetric catalysis using Group 2 metals, moving a step closer to cleaner and inexpensive catalytic processes.