Taming Sustainable Homogeneous Catalysts Through Tailored Diphosphine / Multi-dentate Ligand Design - A Combined Experimental / Computational Study

通过定制二膦/多齿配体设计驯服可持续均相催化剂 - 综合实验/计算研究

• 批准号: 2457159
• 金额: --
• 依托单位: Durham University
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2020
• 资助国家: 英国
• 起止时间: 2020 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-2457159
• 关键词: Taming; Sustainable; Homogeneous; Catalysts; Through

BackgroundIn the catalysis arena there is a considerable impetus to replace use of the precious metals, particularly Pd, Pt, Rh, Ir, and Ru, not only on a cost basis, but also because their supply will become increasingly limited in the coming years. This has led to a renaissance in the study and use of first row d-block elements, especially titanium, vanadium, chromium, manganese, iron, cobalt, nickel, and copper, which are some of the most abundant metals in the earth's crust. In this respect, several cobalt complexes, in the form of either well-defined molecular systems or in situ-formed complexes, are receiving increasing attention from the chemistry community in a range of catalytic application. Compared to its heavier congeners, cobalt is much less expensive and more available because of its production as a by-product of copper and nickel mining/extraction. While the use of the lighter, earth-abundant d-block elements such as cobalt is attractive, their chemistry is more complex than that of the noble metals. Often (homogeneous) catalysts based on metals such as cobalt lack predictability and control over their reactivity, largely as a result of the ease with which these first row metals can access various different spin states coupled with their propensity to undergo competitive single electron transfer processes. In order to try and "tame" the reactivity of cobalt- and other first row metal-based catalysts and to understand their reactivity, the use of multidentate ligands is especially important. These types of metal scaffold can be used to moderate and manipulate steric and/or electronic factors, which dictate reactivity. Given the importance of catalytic C-C and C-X bond-forming reactions in both commodity and fine chemical syntheses, today's limited application of Earth-abundant metals in reflects the difficulty of accessing catalytically-relevant redox and geometric manifolds. Experimental ApproachRecently the Dyer group have shown how even very small differences in metal coordination geometry (imposed by the essential diphosphine) governs redox behaviour, which in turn controls essential oxidative addition, reductive elimination, and transmetallation steps required for catalytic C-C and C-X bond formation. This new insight will be used to direct the design of innovative constrained-geometry, electronically- (balancing sigma-donor/pi-acceptor) and sterically-tuned diphosphine and related multi-dentate ligands. For example, in combination with a rigid, bulky backbone, sterically-demanding, electron-rich cyclic substituents will be deployed at phosphorus in order to constrain the geometry at the metal centre, in turn influencing the metals electronic configuration. Coupled with understanding of the coordination and redox chemistry of Earth-abundant main group and transition metals, new versatile, sustainable diphosphine catalyst systems will be accessed. DFT studies will be used to assess the nature of metal-ligand bonding and how this affects geometry and redox chemistry/metal spin state(s), which in turn will drive iterative ligand design. Results will be assessed experimentally using X-ray crystallography; NMR, IR and NIR-UV-Vis spectroscopies; cyclic voltammetry, spectro-electrochemistry and catalysis studies. This project will explore the synthesis, characterisation, and reactivity of a range of cobalt(II) and (I) complexes bearing bidentate ligands (e.g. diphosphines and alpha-diimines) and tailored multi-dentate ligands for potential catalytic applications including C-C/C-X bond-formation and selective olefin oligomerisation. Emphasis will be upon elucidating structure-reactivity correlations and how such parameters impact on access to potentially catalytically relevant CoI and CoII redox states.

背景中，催化竞技场有很大的动力来取代使用贵金属，尤其是PD，PT，RH，IR和RU，这不仅是在成本基础上，而且还因为它们在未来几年的供应将变得越来越有限。这导致了第一行D块元素的研究和使用，尤其是钛，钒，铬，锰，铁，钴，镍和铜，这是地壳中一些最丰富的金属。在这方面，几种以明确定义的分子系统或原位形成的复合物形式的几种钴复合物正在在一系列催化应用中受到化学界的越来越多的关注。与较重的同类产品相比，钴的价格要便宜得多，而且由于其作为铜和镍采矿/提取的副产品而产生的。虽然使用较轻的，丰富的地球d块元素（例如钴）很有吸引力，但它们的化学反应比贵金属的化学反应更为复杂。通常，基于金属（例如钴）的催化剂通常缺乏可预测性和对其反应性的控制，这在很大程度上是由于这些第一行金属可以访问各种不同的自旋状态以及其经历竞争性单电子传递过程的倾向。为了尝试“驯服”钴和其他第一行金属催化剂的反应性并了解其反应性，使用多齿配体的使用尤为重要。这些类型的金属支架可用于中度和操纵空间和/或电子因素，这决定了反应性。鉴于催化C-C和C-X键形成在商品和细化学合成中的重要性，如今对地球量的金属的应用有限反映了访问催化含量相关的氧化还原和几何歧管的困难。实验性进近的染料组表明，金属配位几何形状（由基本双氨施加）中的差异很小，该差异如何控制氧化还原行为，这反过来又控制了催化性C-C-C-X键形成所需的本质氧化添加，还原性消除和经透射步骤。这种新的见解将用于指导创新的约束几何，电子（平衡Sigma-Donor/pi-copperor）和空间调节的二磷蛋白和相关的多义态配体的设计。例如，结合刚性，笨重的骨干，可供电的，富含电子的循环取代基的磷在磷属上，以限制金属中心的几何形状，从而影响金属电子构型。再加上对地球丰富的主要群体和过渡金属的配位和氧化还原化学的理解，将访问新的多功能，可持续的双氨催化剂系统。 DFT研究将用于评估金属配体键合的性质，以及这如何影响几何形状和氧化还原化学/金属自旋态，这又将推动迭代配体设计。结果将使用X射线晶体学实验评估； NMR，IR和NIR-UV-VIS光谱镜；环状伏安法，光谱电化学和催化研究。该项目将探讨一系列钴（II）和（i）配合物配体配体（例如双刺和α-二亚胺）的钴（II）和（i）的综合性，以及针对包括C-C/C-C-C-X键形成和选择性的型催化剂应用的多态型配体的量身定制的多二烯化配体。重点是阐明结构反应性相关性以及此类参数如何影响访问潜在的催化相关的COI和COII氧化还原状态。