"In-Crystallo" Solid-State Molecular Organometallic Chemistry of Methane, Ethane and Propane. Synthesis, Structures and Catalysis in Single-Crystals

甲烷（CH 4）、乙烷（H3CCH 3）和丙烷（H3CCH 2CH 3）等简单轻质烃类是丰富的天然资源。例如，据估计，全世界大约有200兆立方米的甲烷储量。作为现代人类所需的基本化学品和材料的制造原料，简单的碳氢化合物提供了巨大的潜力。然而，虽然据估计，超过95%（按重量计）的使用中的有机化学品来自增值（即，在一小部分简单的碳氢化合物前体中，目前只有3%的产量实际上用于化学制造。剩下的97%只是燃烧其热值（例如运输）或燃烧-这两者都是对自然资源的巨大浪费，也是气候变化（二氧化碳排放）或空气质量侵蚀的重要贡献者。生物甲烷的可用性不断增加，以及向“非常规”页岩气的转变，使有效的轻质烷烃价值稳定变得更加重要，以实现“净零”碳可持续性。轻质烷烃的丰度和潜力之间的这种不匹配是一个重大的基础科学挑战，也是一个巨大的技术机遇。转化这些原料的核心挑战是催化，其中完美的催化剂在低温下活化特定的C-H键，100%转化为所需的产品。这就是挑战所在，因为烷烃是已知的最差、反应性最低的配体之一。这意味着在C-H活化之前，在催化剂（几乎总是金属基）和烷烃之间形成关键相遇络合物是非常具有挑战性的。简单地说，如果这种复合物没有形成，那么C-H活化就不会发生，我们想要对烷烃进行的有价值的化学转化也不会发生。这就是所谓的“前平衡”问题。烷烃和金属中心之间的这种络合物被称为σ络合物，并且使用甲烷、乙烷和丙烷合成它们是该提议的核心。虽然这些问题可以在工业环境中通过使用非均相催化剂的高温和高压来克服，但是这是能量效率低的并且可以导致差的选择性-导致用于产物分离的下游能量成本（据估计，世界总能量消耗的10-15%涉及化学分离）。我们提出可以克服这种“预平衡”限制，正如我们从生物学中所了解到的，通过控制基底不仅与金属中心而且与其直接周围环境（所谓的二级和三级配位层）的相互作用。在这种情况下，我们的建议是通过完全在单晶中而不是溶液中进行合成，反应性和催化来控制，理解和利用这些相互作用。虽然具有挑战性，但这消除了对溶剂的需求（其在与金属结合方面胜过烷烃），并立即在活性位点周围安装了促进烷烃配位的次级微环境。我们将实现这一目标相结合的“在晶体”有机金属化学（由韦勒开创）和计算在固态（usng麦格雷戈的专业知识计算），利用更广泛的相互作用之间的烷烃基板和环境，以指导和最大限度地提高烷烃的结合。一旦建立了将这些简单烷烃结合在金属中心的能力，我们将在一个示范性但具有挑战性的催化反应中展示我们的概念，该反应以100%原子效率的方式为甲烷增加价值：丙烯的氢甲基化。因此，我们的计划提供了基本的新机会，研究反应性，并在催化中的潜在用途，轻烷烃，对化石或生物衍生烷烃的有效碳管理有着更长远的愿景，而不仅仅是简单的燃烧。

The simple, light, hydrocarbons methane (CH4), ethane (H3CCH3) and propane (H3CCH2CH3) are abundant natural resources. For example it has been estimated that there are approximately 200 Trillion m3 of methane reserves world-wide. As manufacturing feedstocks for the essential chemicals and materials that modern humankind needs simple hydrocarbons offer immense potential. However, while it has been estimated that over 95% (by weight) of organic chemicals in use come from adding value to (i.e., valorisation of) a small pool of simple hydrocarbon precursors, only 3% of current production is actually used for chemical manufacturing. The remaining 97% is simply burnt for its calorific value (e.g. transportation) or flared off - both being an incredible waste of a natural resource and also a significant contributor to climate change (CO2 emissions) or erosion of air quality. The increasing availability of bio-methane, and the shift to "non-conventional" shale gas, places even more importance on efficient light alkane valorisation for "net zero" carbon sustainability. This mismatch between the abundance and the potential of light alkanes is a significant fundamental scientific challenge and a huge technological opportunity. At its heart, the challenge of converting these feedstocks is one of catalysis, in which the perfect catalyst activates a specific C-H bond at low temperatures with 100% conversion to a desired product. Herein lies the challenge, as alkanes are some of the very poorest, and least reactive, ligands known. This means forming the key encounter complex, that precedes C-H activation, between the catalyst (nearly always metal-based) and the alkane is very challenging. Simply put, if this complex does not form, then C-H activation does not take place and the valuable chemical transformation that we want to perform on the alkane does not happen. This is a so-called "pre-equilibrium" problem. Such complexes between an alkane and a metal centre are called sigma-complexes and their synthesis using methane, ethane and propane lie at the heart of this proposal. While these problems can be overcome in an industrial setting by high temperatures and pressures using heterogeneous catalysts, this is energy inefficient and can lead to poor selectivity - leading to a downstream energy cost for product separation (it has been estimated that 10-15% of the world's total energy consumption is involved in chemical separations).We propose that this "pre-equilibrium" limitation can be overcome, as we have learned from biology, by controlling interaction of the substrate with not only the metal centre but also its immediate surrounding environment, the so-called secondary and tertiary coordination spheres. In this context, our proposal is to control, understand and utilise these interactions by performing synthesis, reactivity and catalysis entirely in the single crystal, rather than solution. While challenging, this removes the need for solvent (that outcompetes the alkane for binding to the metal) and immediately installs the secondary microenvironment around the active site that encourages alkane coordination. We will achieve this by a combination of "in crystallo" organometallic chemistry (pioneered by Weller) and calculations in the solid-state (usng Macgregor's expertise in computation) which harness the more diffuse interactions between the alkane substrate and the wider environment to both guide and maximise alkane binding. Once the ability to bind these simple alkanes at metal centres is established we will demonstrate our concept in an exemplar, but challenging, catalytic reaction that adds value to methane in an 100% atom efficient manner: the hydromethylation of propene.Our programme thus offers fundamental new opportunities to study the reactivity, and potential use in catalysis, of light alkanes, with a longer term vision for the efficient carbon-management of fossil- or bio-derived alkanes beyond simple burning.