"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(H3CCH3)和丙烷(H3CCH2CH3)等简单、轻烃是丰富的自然资源。例如，据估计，全世界的甲烷储量约为200万亿立方米。作为制造现代人类所需的基本化学品和材料的原料，简单碳氢化合物提供了巨大的潜力。然而，尽管据估计，使用中的有机化学品有95%以上(按重量计)来自对少量简单碳氢化合物前体的增值(即作价)，但目前生产的产品中只有3%实际用于化学制造。剩下的97%只是为了其热值而燃烧(例如交通工具)或燃烧起来--这两者都是对自然资源的难以置信的浪费，也是气候变化(二氧化碳排放)或空气质量下降的重要原因。随着生物甲烷可获得性的不断提高，以及向“非常规”页岩气的转变，对于实现“净零”碳可持续性的高效低碳烷烃价态变得更加重要。低碳烷烃的丰度和潜力之间的这种不匹配是一个重大的基础性科学挑战和巨大的技术机遇。转化这些原料的核心挑战是催化，在催化过程中，完美的催化剂在低温下激活特定的C-H键，100%转化为所需产品。这就是挑战所在，因为烷烃是已知的最差、活性最低的配体之一。这意味着在催化剂(几乎总是基于金属的)和烷烃之间形成C-H活化之前的关键接触络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“预均衡”问题。烷烃和金属中心之间的这种络合物被称为西格玛络合物，它们是用甲烷、乙烷和丙烷合成的，是这一提议的核心。虽然这些问题可以在工业环境中通过使用多相催化剂的高温和压力来克服，但这是能源效率低的，可能导致选择性差-导致下游产品分离的能量成本(据估计，世界总能耗的10%-15%涉及化学分离)。我们从生物学中了解到，通过控制底物与金属中心以及与其邻近的周围环境的相互作用，我们建议可以克服这种预平衡限制，即所谓的二、三配位球。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(在与金属结合方面胜过烷烃)的需要，并立即在活性中心周围安装辅助微环境，鼓励烷烃配位。我们将通过“晶体中”有机金属化学(由Weller首创)和固态计算(利用Macgregor在计算方面的专业知识)的组合来实现这一点，后者利用烷烃基质和更广泛的环境之间更广泛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，我们将在一个示范的、但具有挑战性的催化反应中展示我们的概念，该反应以100%原子效率的方式增加甲烷的价值：丙烯的氢甲基化。因此，我们的计划提供了根本的新机会来研究低碳烷的反应性和潜在的催化用途，并着眼于在简单燃烧之外对化石或生物衍生的烷烃进行有效的碳管理。

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