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

甲氧羰基化是一种将廉价、广泛可用的原料（烯烃、一氧化碳和甲醇）转化为化工行业重要的商业中间体的过程。该工艺使用钯基催化剂，最好的例子是最简单的烯烃乙烯反应生成用于合成塑料的中间体甲基丙烯酸甲酯。最近，像醋酸乙烯这样的烯烃已被证明经过甲氧羰基化以产生中间体，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。丁二烯的甲氧羰基化反应为合成己二酸提供了一条新的途径。己二酸是生产尼龙的共聚单体之一。迄今为止，醋酸乙烯和丁二烯的甲氧羰基化尚未得到优化，在有效的工业工艺到位之前，需要对这些反应有更深入的了解。甲氧羰基化反应中一个有待解决的关键问题是产物释放的详细机制，即所谓的甲醇分解步骤。这个过程有几种可能性，然而，由于反应本身非常快，很难从实验中获得有关这方面的信息。在这种情况下，计算模型的使用就有了用武之处，因为它可以很容易地提供有关参与反应的物质能量的信息。然而，甲醇分解反应是非常复杂的，并且在很大程度上取决于反应物质的确切性质和所用溶剂的性质。为了获得可靠的建模数据，必须考虑到这些因素，这使得对这些系统建模的任务非常具有挑战性。本研究旨在利用高水平的计算模型来评估最简单的甲氧羰基化体系（乙烯/CO/MeOH）和最有效的钯催化剂上甲醇分解的机理。我们的方法将采用混合计算，其中催化剂和反应分子在高水平的理论（密度泛函理论）中处理，而溶剂分子（许多10或数百）在基于经典力场的较低水平的理论中处理。通过这种方法，溶剂对钯催化剂反应性的影响将被考虑在内，我们的目标是提供非常可靠的数据来确定首选机制。我们将通过与显示不同反应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。一旦我们确定了处理这些复杂反应的正确方法，以及甲醇分解发生的机制，我们就可以处理醋酸乙烯和丁二烯的新反应了。我们希望对这些过程提供足够的见解，以便实验化学家能够设计出新的改进催化剂，以便在工业规模上更有效地对这些原料进行甲氧羰基化。

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.