"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.

简单、轻质的碳氢化合物甲烷（CH4）、乙烷（H3CCH3）和丙烷（H3CCH2CH3）是丰富的自然资源。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，虽然据估计超过 95%（按重量计）的有机化学品来自于一小部分简单碳氢化合物前体的增值（即增值），但当前产量中只有 3% 实际上用于化学品制造。剩下的 97% 只是为了获取热值而燃烧（例如运输）或烧掉——这既是对自然资源的极大浪费，也是气候变化（二氧化碳排放）或空气质量恶化的重要原因。生物甲烷的可用性不断增加，以及向“非常规”页岩气的转变，使得轻质烷烃的高效增值对于“净零”碳可持续性变得更加重要。轻质烷烃的丰度与潜力之间的不匹配是一项重大的基础科学挑战，也是一个巨大的技术机遇。从本质上讲，转化这些原料的挑战之一是催化，其中完美的催化剂在低温下激活特定的 C-H 键，并 100% 转化为所需的产品。这就是挑战，因为烷烃是已知最差且反应性最差的配体之一。这意味着在催化剂（几乎总是金属基）和烷烃之间形成 C-H 活化之前的关键相遇络合物非常具有挑战性。简而言之，如果不形成这种复合物，则不会发生 C-H 活化，并且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“预平衡”问题。这种烷烃和金属中心之间的络合物被称为西格玛络合物，它们使用甲烷、乙烷和丙烷的合成是该提案的核心。虽然这些问题可以在工业环境中使用多相催化剂通过高温高压来克服，但这种方法能源效率低下，并且可能导致选择性差，从而导致产品分离的下游能源成本（据估计，化学分离涉及世界总能源消耗的 10-15%）。我们建议，正如我们从生物学中了解到的那样，可以通过控制 基底不仅具有金属中心，而且还具有其直接周围的环境，即所谓的二级和三级配位球。在这种情况下，我们的建议是通过完全在单晶而不是溶液中进行合成、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（在与金属的结合方面胜过烷烃），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。我们将通过“晶体”有机金属化学（由 Weller 首创）和固态计算（利用 Macgregor 的计算专业知识）相结合来实现这一目标，利用烷烃底物和更广泛的环境之间更分散的相互作用来引导和最大化烷烃结合。一旦建立了在金属中心结合这些简单烷烃的能力，我们将在一个示例性但具有挑战性的催化反应中展示我们的概念，该催化反应以 100% 原子效率的方式为甲烷增加价值：丙烯的氢甲基化。因此，我们的计划为研究轻质烷烃的反应性和催化中的潜在用途提供了根本性的新机会，并为化石或烷烃的有效碳管理提供了长期愿景。 超越简单燃烧的生物衍生烷烃。

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