Realistic Modelling of Organometallic Reactivity in Solution: Computational Studies on the Mechanism of Methanolysis of Palladium-Acyl Bonds

甲氧基化是一种将廉价的、可广泛获得的原料(烯烃、一氧化碳和甲醇)转化为对化学工业具有商业重要性的中间体的过程。这一过程使用以钯为基础的催化剂，最好的例子是由最简单的烯烃-乙烯反应生成中间体甲基丙烯酸甲酯，用于合成塑料。最近，如乙酸乙烯酯这样的烯烃已被证明经过甲氧羰化反应生成中间体，这些中间体本身可用作绿色溶剂(低挥发性/可生物降解)或作为形成可生物降解聚合物的单体。这些材料有可能取代聚苯乙烯或聚乙烯等传统材料。丁二烯的甲氧基化有望提供一条合成己二酸的新途径，己二酸是制造尼龙的共聚单体之一。到目前为止，乙酸乙烯和丁二烯的甲氧羰化反应还没有得到优化，在有效的工业过程到位之前，需要对这些反应有更深入的了解。甲氧羰化反应中有待解决的一个关键问题是产品释放的详细机制-所谓的甲烷分解步骤。这个过程有几种可能性，然而，从实验中获得有关这方面的信息是极其困难的，因为反应本身是令人难以置信的快速的。在这种情况下，计算模型的使用就应运而生了，因为它可以很容易地提供有关参与反应的物种的能量的信息。然而，甲烷分解反应是非常复杂的，并且强烈依赖于反应物种的确切性质和所使用的溶剂的性质。为了获得可靠的模拟数据，必须考虑这些因素，这一事实使得模拟这些体系的任务非常具有挑战性。这项建议寻求使用高水平的计算模拟来评估最简单的甲氧羰化体系-乙烯/CO/MeOH-和最有效的Pd催化剂上的甲烷分解机理。我们的方法将是使用混合计算，其中催化剂和反应分子在高水平的理论(密度泛函理论)下处理，而溶剂分子(许多是10或数百)在基于经典力场的低水平理论中处理。通过这种方法，将考虑溶剂对Pd催化剂反应活性的影响，我们的目标是提供极其可靠的数据来确定首选的反应机理。我们将通过与表现出不同反应活性的替代催化剂进行比较来测试我们的方法，从而对我们的建模方法进行严格的测试。一旦我们定义了处理这些复杂反应的正确方法-以及发生甲烷分解的机理-我们就可以处理乙酸乙烯和丁二烯的新反应。我们希望为这些过程提供足够的洞察力，以便实验化学家能够设计出新的改进的催化剂，以便在工业规模上更有效地进行这些原料的甲氧基化反应。

Methoxycarbonylation is a process that converts cheap, widely available feedstocks (alkenes, carbon monoxide and methanol) into commercially-important intermediates for the chemicals industry. This process uses Pd-based catalysts and the best example is the reaction of the simplest alkene, ethene, to give the intermediate methyl methacrylate, which is used in the synthesis of plastics. More recently, alkenes such as vinyl acetate have been shown to undergo methoxycarbonylation to generate intermediates that are themselves useful as green solvents (low-volatility/biodegradable) or as monomers for the formation of biodegradable polymers. These have the potential to replace traditional materials such as polystyrene or polythene. Methoxycarbonylation of butadiene promises a new route to adipic acid, one of the co-monomers involved in the manufacture of nylon. As yet the methoxycarbonylation of vinyl acetate and butadiene have not been optimised and greater insight into these reactions is required before effective industrial processes are in place.A key issue that remains to be solved in the methoxycarbonylation reaction is the detailed mechanism by which the products are released - the so-called methanolysis step. There a several possibilities for this process, however, it is extremely difficult to obtain information on this from experiment as the reaction itself is incredibly fast. In these circumstances the use of computational modelling comes into its own, as this can readily provide information on the energies of the species involved in reactivity. The methanolysis reaction is, however, very complicated and is strongly dependent on the precise nature of the reacting species and the nature of the solvent being used. To obtain reliable modelling data these factors must be taken into account, a fact that makes the task of modelling these systems very challenging.This proposal seeks to use high level computational modelling to assess the mechanism of the methanolysis on the simplest methoxycarbonylation system - ethene/CO/MeOH - and the most effective Pd catalysts. Our approach will be to employ hybrid calculations where the catalyst and reacting molecules are dealt with at a high level of theory (density functional theory) but the solvent molecules (many 10s or hundreds) are treated at a lower level of theory based on classical force fields. Through this approach the effect of the solvent on the reactivity at the Pd catalyst will be taken into account and we aim to provide extremely reliable data to define the preferred mechanism. We will test our approach by comparing with an alternative catalyst which displays a different reactivity, thus giving a stringent test of our modelling approach.Once we have defined the correct way to treat these complicated reactions - as well as the mechanism by which methanolysis occurs - we will be in a position to tackle the new reactions of vinyl acetate and butadiene. We hope to provide sufficient insight into these processes that experimental chemists will be able to design new improved catalysts for more efficient methoxycarbonylation of these feedstocks on an industrial scale.