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

甲烷、乙烷和丙烷的“晶体内”固态分子有机金属化学。

• 批准号: EP/W015552/1
• 负责人: Andrew Weller
• 金额: $ 67.08万
• 依托单位: University of York
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2022
• 资助国家: 英国
• 起止时间: 2022 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=EP%2FW015552%2F1
• 关键词: Crystallo; Solid; State; Molecular; Organometallic

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.

甲烷（CH4）、乙烷（H3CCH2CH3）和丙烷（H3CCH2CH3）是简单、轻的碳氢化合物，是丰富的天然资源。例如，据估计，全世界大约有200万亿立方米的甲烷储量。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，据估计，使用中的有机化学品95%以上（按重量计算）来自对一小部分简单碳氢化合物前体的增值（即增值），目前只有3%的产量实际用于化学制造。剩下的97%只是为了其热值而燃烧（例如运输）或燃烧-这都是对自然资源的不可思议的浪费，也是对气候变化（二氧化碳排放）或空气质量侵蚀的重要贡献者。生物甲烷的日益普及，以及向“非常规”页岩气的转变，使得轻质烷烃的高效增值对“净零”碳可持续性更加重要。轻烷烃的丰度和潜力之间的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作用，其中完美的催化剂在低温下激活特定的C-H键，并100%转化为所需产品。这就是挑战所在，因为烷烃是已知的最穷、最不活泼的配体。这意味着在催化剂（几乎都是金属基的）和烷烃之间形成碳氢活化之前的关键相遇复合物是非常具有挑战性的。简单地说，如果这个络合物没有形成，那么碳氢活化就不会发生我们想要在烷烃上进行的有价值的化学转化就不会发生。这就是所谓的“前均衡”问题。这种介于烷烃和金属中心之间的配合物被称为西格玛配合物，用甲烷、乙烷和丙烷合成它们是这个提议的核心。虽然这些问题可以在工业环境中通过高温和高压使用多相催化剂来克服，但这是能源效率低下的，可能导致选择性差-导致产品分离的下游能源成本（据估计，世界上总能源消耗的10-15%涉及化学分离）。我们提出，正如我们从生物学中所学到的，这种“预平衡”限制可以通过控制底物与金属中心以及其直接周围环境（所谓的二级和三级配位球）的相互作用来克服。在这种情况下，我们的建议是通过完全在单晶中而不是在溶液中进行合成、反应和催化来控制、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（溶剂比烷烃更容易与金属结合），并立即在活性位点周围安装二级微环境，以促进烷烃的配位。我们将通过结合“结晶”有机金属化学（由韦勒首创）和固态计算（使用麦格雷戈的计算专业知识）来实现这一目标，后者利用烷烃底物和更广泛的环境之间更分散的相互作用来指导和最大化烷烃结合。一旦在金属中心结合这些简单烷烃的能力建立起来，我们将在一个范例中展示我们的概念，但具有挑战性，催化反应以100%原子效率的方式增加甲烷的价值：丙烯的氢甲基化。因此，我们的项目为研究轻烷烃的反应性及其在催化方面的潜在用途提供了基本的新机会，并为化石或生物衍生烷烃的有效碳管理提供了更长远的愿景，而不仅仅是简单的燃烧。

项目成果

A comparison of non-covalent interactions in the crystal structures of two s-alkane complexes of Rh exhibiting contrasting stabilities in the solid state

Rh 的两种 s-烷烃配合物晶体结构中非共价相互作用的比较，表现出不同的固态稳定性

• DOI: 10.1039/d3fd00009e
• 发表时间: 2023
• 期刊: Faraday Discussions
• 影响因子: 3.4
• 作者: Sajjad M