Homogeneous hydrogenation of nitrous oxide

一氧化二氮（N2O）是一种富集在地球大气中的丰富气体，作为一种强有力的温室气体，它会导致平流层臭氧的消耗，并加剧全球变暖。虽然一氧化二氮是自然产生的，但由于农业密集施肥、工业过程以及化石燃料和生物质的燃烧，一氧化二氮的排放不断增加，这将对我们的环境产生有害影响，因此是一个令人担忧的主要原因。氧化亚氮的加氢是一种很有吸引力的化学修复方法，它由对环境无害的二氮和水的释放驱动（方案1）。虽然一系列的多相系统已被证明可以催化该反应，但温和的条件和对精确反应控制的倾向与均相催化同义，使这些变体从修复的角度来看是最理想的。此外，由于均相催化剂的机理可以更容易地研究，它们可以提供一个平台，揭示与N2O如何被激活和潜在地用于（增值）合成应用相关的重要基础化学。虽然N2O的化学性质长期以来一直受到关注，但由于该气体具有强大的三原子结构，因此使用过渡金属化合物进行催化转化已被证明具有挑战性。根据华威大学化学系最近的文献进展和基础工作（方案1），该项目将涉及开发新的晚期过渡金属基催化剂，用于氧化亚氮的均匀加氢，首先使用分子二氢，但长期来看，使用可持续或生物质衍生的化学品。方法：Milstein最近的工作证实了金属氢化物对N2O的N-O键活化的倾向，并表明与双功能“钳形”配体结合，可以实现催化加氢。在这些设计原则的基础上，并在卓别林小组的专业知识的帮助下，该项目的第一步将是系统地研究过渡金属氢化物配合物与N2O的反应，这些配合物由三叉戟“钳形”配体或其他具有活性氨基（M=NR2）或磷酸（M=PR2）键的螯合变体支持。结合催化活性的评估，本工作将用于建立N2O加氢的结构活性关系，为设计和合成新的更有效的催化剂提供信息。为了补充这项工作，将使用N2O作为底物筛选已建立的转移氢化催化剂，寻求开发使用牺牲有机分子（如乙醇）作为储氢源的修复程序。

Nitrous oxide (N2O) is an abundant gas that accumulates in the Earth's atmosphere, leading to depletion of ozone in the stratosphere and contributing to global warming as a potent greenhouse gas. Although naturally occurring, increasing N2O emissions resulting from intensive agricultural fertilisation, industrial processes, and combustion of fossil fuels and biomass are a major cause for concern due to the detrimental impact this will have on our environment. The hydrogenation of nitrous oxide is an attractive chemical remediation method, driven by the release of environmentally benign dinitrogen and water (Scheme 1). Whilst a range of heterogenous systems have been shown to catalyse this reaction, the mild conditions and propensity for precise reaction control synonymous with homogenous catalysis make these variants the most desirable from a remediation perspective. Moreover, as the mechanisms of homogenous catalysts can be more readily studied, they can provide a platform for shedding light on important fundamental chemistry associated with how N2O can be activated and potentially exploited in (value added) synthetic applications. Whilst the chemistry of N2O has been of longstanding interest, its catalytic transformation using transition metal compounds has proven to be challenging due to the robust triatomic formulation of this gas. Building upon recent developments in the literature and underpinning fundamental work conducted in the Department of Chemistry at the Univeristy of Warwick (Scheme 1), this project will involve the development of new late-transition-metal-based catalysts for the homogenous hydrogenation of nitrous oxide using, in the first instance molecular dihydrogen, but with a long term view to the use of sustainable or biomass-derived chemicals, from which hydrogen can be extracted directly (transfer hydrogenation)Methodology: Recent work by Milstein has substantiated the propensity of metal hydrides for N-O bond activation of N2O and shown that in combination with bifunctional "pincer" ligands, catalytic hydrogenation can be achieved. On the basis of these design principles and facilitated by expertise in the Chaplin group, the first step of the project will be to systematic study the reaction of transition metal hydride complexes, supported by tridentate "pincer" ligands or other chelating variants bearing reactive amido (M=NR2) or phospido (M=PR2) linkages, with N2O. In combination with evaluation of catalytic activity, this work will be used to establish structure activity relationships for the hydrogenation of N2O to inform the design and synthesis of new more effective catalysts. Complementing this work, established transfer hydrogenation catalysts will be screened using N2O as the substrate, seeking to develop procedures for remediation that use sacrificial organic molecules, e.g. ethanol, as hydrogen reservoirs.