Homogeneous hydrogenation of nitrous oxide

一氧化二氮（N2 O）是一种丰富的气体，在地球大气层中积累，导致平流层臭氧消耗，并作为一种强有力的温室气体导致全球变暖。虽然是自然发生的，但由于密集的农业施肥，工业过程以及化石燃料和生物质的燃烧而导致的N2 O排放量增加是一个令人担忧的主要原因，因为这将对我们的环境产生不利影响。一氧化二氮的氢化是一种有吸引力的化学修复方法，由环境友好的二氮和水的释放驱动（方案1）。虽然一系列非均相系统已被证明可以催化该反应，但温和的条件和与均相催化同义的精确反应控制倾向使这些变体从修复的角度来看是最理想的。此外，由于可以更容易地研究均相催化剂的机制，它们可以提供一个平台，用于阐明与N2 O如何被活化和在（增值）合成应用中潜在利用相关的重要基础化学。虽然N2 O的化学性质长期以来一直受到关注，但由于这种气体的稳定的三原子配方，使用过渡金属化合物进行催化转化已被证明具有挑战性。建立在文献的最新发展和基础工作进行化学系在沃里克大学（方案1），该项目将涉及开发新的后过渡金属基催化剂，用于一氧化二氮的均相氢化，首先使用分子二氢，但从长远来看，使用可持续的或生物质衍生的化学品，可以直接从中提取氢（转移氢化）方法：Milstein最近的工作证实了金属氧化物对N2 O的N-O键活化的倾向，并表明与双官能“钳”配体结合，可以实现催化氢化。根据这些设计原则，并借助卓别林小组的专门知识，该项目的第一步将是系统地研究过渡金属氢化物络合物与N2 O的反应，该络合物由三齿“钳形”配体或其他带有反应性酰胺基（M= NR 2）或磷基（M= PR 2）键的螯合变体支持。结合催化剂活性的评价，本工作将用于建立N2 O加氢的构效关系，为设计和合成新的更有效的催化剂提供信息。作为这项工作的补充，将使用N2 O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（例如乙醇）作为氢库的修复程序。

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.