Optimisation of Palladium-Catalysed C-H Activation Reactions

钯催化的C-H活化化学提供了减少与合成相关的浪费和成本的手段。与传统使用的交叉偶联相比，这通过缩短合成路线来实现。然而，存在于文献中的这种化学的大多数实例的特征在于高反应温度和长反应持续时间。很少使用非均相催化剂，这意味着催化剂分离具有挑战性，通常需要使用清除剂或二氧化硅纯化。这在产品必须符合某些标准的情况下是特别重要的，例如钯只能以每克API 10微克的水平存在于API中。钯是一种稀有且昂贵的金属，通过从均相来源转移到非均相来源，最大限度地提高其重复利用率，并最大限度地减少其在化学产品中的保留，将是有利的。为了最大限度地提高钯催化的C-H活化的效率，需要在不损害产品质量的情况下最小化温度和/或反应持续时间。建议的解决方案和方法已经提出了一套补充条件来解决手头的问题。涉及多相催化、微波加热和流动化学，多相催化将用于实现更好的催化剂重复使用和分离。多相催化剂的使用开辟了选择性加热与微波加热相结合时的可能性。这允许更容易地达到高反应温度，从而减少反应持续时间。具有合适介电性质的固体载体应有利地吸收微波能量，在催化剂位置处快速加热。微波必须能够穿透反应混合物以有效加热，因此，使用微波加热散装混合物是具有挑战性的。为了增加规模，还提出了一种流动系统，通过在给定时刻最小化反应体积来确保微波加热在规模上保持效率。此外，这提供了固定催化剂的机会，进一步提高可重复使用性和易于分离。预计所提出的方法将提供一种达到或超过所需温度的方便方法，从而提高反应速率，使这种化学更容易获得和应用，特别是在更大的规模上。

Palladium-catalysed C-H activation chemistry provides a means to reduce waste and cost associated with syntheses. This occurs through the shortening of synthetic routes when compared to traditionally used cross-couplings. However, most examples of this chemistry that exist in literature feature high reaction temperatures and long reaction durations. Heterogeneous catalysts are rarely used, meaning catalyst separation is challenging, usually requiring use of scavengers or purification on silica. This is particularly important where the product must be held to certain standards, for instance palladium can only exist in API's at a level of 10 micrograms per gram of API. Palladium is a rare and expensive metal, it would be advantageous to maximise its re-use, and minimise its retention in chemical products through moving away from homogeneous sources and towards heterogeneous sources.To maximise the efficacy of palladium-catalysed C-H activation, it's desirable that the temperature and/or reaction duration can be minimised, without detriment to the quality of the product. Proposed solution and methodologyA complimentary set of conditions has been proposed to tackle the issues at hand. Involved would be heterogenous catalysis, microwave heating and flow chemistry.Heterogeneous catalysis will be used to achieve better catalyst reusability and separation. The use of a heterogeneous catalyst opens up the possibility of selective heating when coupled with microwave heating. This allows the high reaction temperatures to be accessed more easily, subsequently reducing reaction duration. A solid support with suitable dielectric properties should favourably absorb microwave energy, rapidly heating at the location of the catalyst. Microwaves must be able to penetrate the reaction mixture to heat effectively, therefore, heating a bulk mixture is challenging using microwaves. In order to increase the scale, a flow system is also proposed to ensure microwave heating maintains efficiency at scale, by minimising the reaction volume at a given moment. Additionally, this provides the opportunity to immobilise the catalyst, further enhancing reusability and ease of separation.It is anticipated that the proposed methodology will provide a convenient way of reaching or exceeding the desired temperatures, thus enhancing the reaction rate and making this chemistry more accessible and applicable, especially on a larger scale.