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

甲氧基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）转化为化学工业的商业上重要的中间体的工艺。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中间体甲基丙烯酸甲酯，用于合成塑料。最近，烯烃如乙酸乙烯酯已显示经历甲氧基羰基化以产生中间体，所述中间体本身可用作绿色溶剂（低挥发性/可生物降解的）或用作形成可生物降解的聚合物的单体。这些材料有可能取代聚苯乙烯或聚乙烯等传统材料。丁二烯的甲氧基羰基化有望成为生产己二酸的新途径，己二酸是尼龙生产中涉及的共聚单体之一。到目前为止，乙酸乙烯酯和丁二烯的甲氧基羰基化反应还没有得到优化，在有效的工业化工艺到位之前，需要对这些反应有更深入的了解。在甲氧基羰基化反应中仍有待解决的一个关键问题是产物释放的详细机制-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，因此很难从实验中获得有关信息。在这种情况下，计算模型的使用就显得很重要，因为这可以很容易地提供有关反应性所涉及的物质能量的信息。然而，甲醇分解反应非常复杂，并且强烈依赖于反应物质的精确性质和所用溶剂的性质。为了获得可靠的建模数据，这些因素必须考虑到，一个事实，使这些系统建模的任务非常具有挑战性的，这个建议旨在使用高层次的计算建模，以评估最简单的甲氧基羰基化系统-乙烯/CO/MeOH -和最有效的Pd催化剂上的甲醇分解的机制。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，但溶剂分子（许多10或数百）在较低水平的理论基础上处理经典力场。通过这种方法，溶剂对Pd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定义优选的机制。我们将通过与具有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理-我们将能够处理醋酸乙烯酯和丁二烯的新反应。我们希望提供足够的洞察这些过程中，实验化学家将能够设计新的改进催化剂，更有效地在工业规模上的这些原料的甲氧基羰基化。

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.