Transition Metal Alkane Sigma Complexes by Solid-Gas Synthesis Routes: Defining and Exploiting a New Area of Organometallic Chemistry

烷烃是廉价和容易获得的化学品，化学研究的一个长期目标是开发方法，将这些物种直接用作化学原料。这将极大地提高化学合成的整体效率，用于生产支撑化学工业和制药业的商品和精细化学品。为了实现这一目标，需要“激活”(即破坏)臭名昭著的无活性C-H键的方法。虽然近年来已经报道了用过渡金属络合物进行这种C-H活化的例子，但在将C-H活化完全整合到化学合成中之前，还需要更多关于这一过程的信息。通过研究烷烃在实际断裂C-H键之前与金属中心相互作用的方式，可以获得许多有用的见解。这就需要有手段来制备和研究这种所谓的“过渡金属烷烃西格玛络合物”；然而，直到最近，由于缺乏直接和可预测的一般制备方法，这类物种的例子极其有限。最近，Weller(实验化学)和Macgregor(计算模拟)研究小组报告了过渡金属烷烃西格玛配合物的合成和表征方面的突破(见Science 2012,337,1648)。我们的方法是让过渡金属烯烃前体在晶态固态下与氢气反应。这直接在结晶状态下产生了等价的烷烃西格玛络合物，允许通过各种实验和互补的计算技术来充分表征它。这代表了目前最先进的过渡金属烷烃西格玛络合物的合成和表征的一步变化，开辟了令人兴奋的前景，第一次可以常规地合成这类物种，并充分理解它们的化学。这项研究建议寻求支持Weller和Macgregor小组全面探索和推广用于合成过渡金属烷烃西格玛络合物的新的气固合成方法。我们的方法将涉及与计算建模相结合的实验合成和表征；后者也提供通过实验手段难以常规获得的结构数据。此外，计算模型可以用来预测过渡金属-烷烃相互作用的强度。这样，计算将能够针对最有希望的组合进行进一步的实验研究，从而显著提高项目的整体生产率。根据我们对过渡金属烷烃西格玛络合物在固态中稳定的原因的理解，我们将着手开发在溶液中也稳定的体系，以便提供关于此类物种的性质和反应活性(即C-H活化)的明确数据。另一种令人兴奋的可能性是探索在气固体系中发生的其他化学转化；例如，具有重要商业意义的烯烃催化氢化可能发生在固态，而不需要恢复使用溶剂。该项目的研究本质上是基础的，但它将通过发展过渡金属烷烃sigma络合物的化学以及这些物种如何与关键的C-H活化过程相关来产生重要的长期遗产。它还将探索固态有机金属化学的发展，不仅在制造新的有机金属超分子络合物方面，而且更广泛地，通过探索在固态中新的催化过程(特别是固-气反应)的潜力。

Alkanes are cheap and readily available chemicals and a long-term goal of chemical research has been to develop methods to exploit these species directly as chemical feedstocks. This would greatly improve the overall efficiency of chemical synthesis used in the production of commodity and fine chemicals that underpin the chemical and pharmaceutical industries. In order to achieve this goal the means to "activate" (i.e. break) the notoriously unreactive C-H bond is required. While examples of such C-H activation with transition metal complexes have been reported in recent years, much more information on this process is required before the integration of C-H activation into chemical synthesis is fully realised. Much useful insight could be gained by studying the way an alkane interacts with a metal centre prior to actually cleaving the C-H bond. This requires the means to prepare and study such so-called 'transition metal alkane sigma complexes'; however, until recently, examples of such species have been extremely limited due to the lack of straightforward and predictable general methods of preparation. Very recently the Weller (experimental chemistry) and Macgregor (computational modelling) research groups have reported a breakthrough in the synthesis and characterisation of transition metal alkane sigma complexes (see Science 2012, 337, 1648). Our approach was to react a transition metal alkene precursor in the crystalline solid-state with hydrogen gas. This produces the equivalent alkane sigma-complex directly in the crystalline state, allowing for its full characterisation by a variety of experimental and complementary computational techniques. This represents a step-change in current state-of-the-art for the synthesis and characterization of transition metal alkane sigma-complexes, opening up the exciting prospect that, for the first time, such species could be routinely synthesized and their chemistry fully understood.This research proposal seeks support for the Weller and Macgregor groups to fully explore and generalise the new gas-solid synthetic methodology for the synthesis of transition metal alkane sigma-complexes. Our approach will involve experimental synthesis and characterisation allied with the computational modelling; with the latter also providing structural data that are difficult to routinely obtain by experimental means. In addition computational modelling can be used to predict how strong the transition metal-alkane interaction will be. In this way the calculations will be able to target the most promising combinations for further study experimentally, thus significantly enhancing the overall productivity of the project. From our understanding of what makes a transition metal alkane sigma complex stable in the solid state we will then move to develop systems that are also stable in solution in order to provide definitive data on the properties and reactivity (i.e. C-H activation) of such species. Another exciting possibility will be to explore what other chemical transformations occur in the gas-solid regime; for example the commercially important catalytic hydrogenation of alkenes may occur in the solid state, without the need to revert to the use of solvents.The research in this project is fundamental in nature, however it will deliver significant long-term legacy through developing the chemistry of transition metal alkane sigma-complexes and how such species relates to the key C-H activation process. It will also explore the development of solid-state organometallic chemistry, both in terms of making new organometallic supramolecular complexes, but also, more generally, by exploring the potential of new catalytic processes (especially solid-gas reactions) in the solid state.