Reactivity consequences of electronic and spin state effects in organometallic chemistry

我提出了一个综合的合成、机械和计算研究，以选择性地探索电子构型和自旋态对有机金属催化基本化学计量反应的影响。金属性质和配体设计的仔细相互作用将允许化合物的合成，其中对配体球体外围的空间和/或电子修饰将调整金属中心的轨道分裂和配对能量，无论是通过感应还是通过调整配位几何，从而选择性地调整化合物的自旋态能量。这将允许在相似的配位环境中合成具有相同金属和氧化态的对或系列化合物，但基态自旋不同，允许系统的机制研究复合物的自旋状态如何单独影响组成有机金属催化循环的反应的热力学和动力学。合理设计用于有机合成和工业应用的催化剂仍然是有机金属化学的主要焦点。催化剂的自旋状态有可能发挥关键作用，因为未配对电子的存在或在不同自旋表面之间交叉的需要会对反应的能量、机制和速率产生深远的且通常是意想不到的影响。最近开发的越来越多的催化体系，特别是在烯烃聚合领域，采用第一行金属的中价化合物，如Cr、Fe和Co，产生的催化剂或催化剂前体不仅具有顺磁基态，而且在催化循环中可以在不同的自旋表面之间交叉。越来越多的研究表明，自旋交叉现象将在有机金属催化中发挥巨大的作用。因此，本研究的主要目标是首次系统地分离和调查自旋状态单独影响和控制有机金属反应性的方法，并展示这种控制可能被利用的具体实例。目前正在研究与烯烃聚合化学相关的两个明确的体系。它们是二（恶唑啉基）吡啶二烷基铁（II）（传统的齐格勒-纳塔聚合）和二（氨基酸酯）和二（β -酮胺）单烷基钴（III）配合物（原子转移和有机金属自由基聚合）。两者都是五坐标，16价电子系统和6个d壳层电子，但在每种情况下都有多种可能的基态自旋，最可能的构型是开壳层五重体和闭壳层单重态。在每种情况下，配体都很容易被修饰以承受各种不同空间分布的供/吸电子基团，从而可以控制所展示的自旋性质。这将允许对基本的有机金属反应进行并排比较，其中一个反应发生在单个抗磁性自旋表面上，而另一个反应发生在完全顺磁性表面上，或者需要从一个自旋状态切换到另一个自旋状态。配位、插入和消除等反应与Z-N聚合机制有关，而单电子和原子转移反应在ATRP和OMRP中很重要。采用DFT的计算研究将指导实验研究系统的选择，并有助于解释和支持机制结果。这种调查方法非常适合与UBC奥肯那根大学当前本科研究相关的资源，但随着我们研究生课程的发展，将很容易应用于长期研究。提出的目标化合物是几个简单的合成步骤，从商业上可用和廉价的材料。配体系统很容易修改，允许快速开发各种化合物。该研究的综合性质将使学生体验有机和有机金属的合成和表征，利用紫外可见和核磁共振光谱技术进行机理研究，以及计算方法。尽管它们的基础相对简单，但我相信这些研究具有巨大的意义，并且将产生的结果将大大增强开壳顺磁性过渡金属催化剂的合理设计。

I propose an integrated synthetic, mechanistic, and computational study to probe selectively the effects of electronic configuration and spin state on the stoichiometric reactions fundamental to organometallic catalysis.  Careful interplay of metal properties and ligand design will allow for the synthesis of compounds wherein steric and/or electronic modification to the periphery of the ligand sphere will adjust the orbital splitting and pairing energies at the metal centre, either inductively or by adjusting the coordination geometry, thereby selectively tuning the spin state energies of the compound.  This will allow for the synthesis of pairs or series of compounds with identical metals and oxidation states in similar coordination environments, but differing ground state spin, permitting a systematic mechanistic study of how the spin state of a complex alone affects the thermodynamics and kinetics of the reactions that make up organometallic catalytic cycles.The rational design of catalysts for synthetic organic and industrial applications continues to be a principal focus of organometallic chemistry.  The spin state of the catalyst has the potential to play a critical role, in that the presence of unpaired electrons or the need to cross over between surfaces of different spin can have a profound and often unexpected effect on the energies, mechanisms, and rates of reactions.  An increasing number of recently developed catalytic systems, particularly those in the area of alkene polymerization, employ mid-valent compounds of first-row metals such as Cr, Fe, and Co, yielding catalysts or catalyst precursors that not only have paramagnetic ground states, but also may cross between different spin surfaces during the catalytic cycle.  An increasing body of work suggests that spin crossover phenomena will prove to play an enormous role in organometallic catalysis.  The principal goal of this research is therefore the first systematic study to isolate and investigate the means by which spin state alone can affect and control organometallic reactivity generally, and to demonstrate specific instances in which this control might be exploited.Two well-defined systems of relevance to alkene polymerization chemistry are currently under investigation.  These are bis(oxazolinyl)pyridine dialkyl iron(II) (traditional Ziegler-Natta polymerization), and bis(amidinate) and bis(beta-ketoamine) monoalkyl cobalt(III) complexes (atom transfer and organometallic radical polymerization).  Both are five-coordinate, 16 valence electron systems with six d-shell electrons, but in each case there are multiple possible ground state spins, with the most likely configurations being the open-shell quintet and closed-shell singlet.  In each case, the ligands are easily modified to bear a variety of electron donating/withdrawing groups of varying steric profile, which affords control of the exhibited spin properties.  This will permit a side-by-side comparison of fundamental organometallic reactions, whereby one reaction takes place on a single diamagnetic spin surface, while the other takes place on either a wholly paramagnetic surface or requires a crossover from one spin state to another.  Reactions such as coordination, insertion, and beta-elimination are of relevance to Z-N polymerization mechanisms, while single-electron and atom transfer reactions are important in ATRP and OMRP.  Computational studies employing DFT will both guide the choice of systems for experimental investigation, and serve to interpret and support the mechanistic results.This approach of investigation is well suited to the resources associated with current undergraduate research at UBC Okanagan, but will easily be applied to longer-term studies as our graduate programme develops.  The proposed target compounds are a few simple synthetic steps from commercially available and inexpensive materials.  The ligand systems are easily modified, allowing a wide range of compounds to be developed quickly.  The integrated nature of the study will give students experience with organic and organometallic synthesis and characterization, mechanistic studies using UV-visible and NMR spectroscopic techniques, and computational methods.  Despite their relatively simple basis, I believe these studies have dramatic implications, and will yield results that will greatly enhance the rational design of open-shell paramagnetic transition-metal catalysts.