Solid-state molecular Organometallic Chemistry of Group 7 Carbonyls: Taming Reactive Complexes in an Anionic Cage

背景：有机金属的合成、反应和催化几乎总是在溶液相进行，在溶液相中，感兴趣的络合物或催化剂被溶解在所选择的溶剂中。虽然这很方便，但这往往意味着催化中非常活跃的中间体或合成中的络合物很难观察，更不用说分离了，因为溶剂经常与金属中心结合或不可逆转地发生反应。Weller小组最近开发了一种避免溶剂结合的技术，从而分离、表征和研究无法通过传统溶液路线制备的高活性络合物。这项技术看起来很简单：所有的化学、表征、反应甚至催化都是在单晶到单晶的转化中进行的，在单晶转化中，气体穿透晶体并与金属中心反应生成目标络合物，或者经历感兴趣的催化转化。我们称之为固态分子金属有机化学(SMOM-Chem)。例如，这种方法允许合成阳离子西格玛-烷烃络合物，这是C-H活化过程中的关键-但通常是瞬时的-中间体。一个稳定的[BArF4]-阴离子在晶格中的反应性阳离子(类似于酶的反应部位)周围的“纳米反应器”是关键。这种方法的威力体现在这样的烷烃化合物的合成上，这些化合物在克级尺度上在室温下无限稳定，而在溶液中的寿命在-100摄氏度和镁含量下(最好)是几分钟。因此，SMOM技术可以分离“不可能”的络合物。目的：到目前为止，这种化学主要集中在第9族络合物。问题是，SMOM化学能否扩展到其他过渡金属，以及能否开发出非常活跃、具有合成挑战性和催化活性的体系？我们将在一个令人兴奋的新项目中回答这个问题，该项目将SMOM技术与第7族阳离子(Mn，Re)相结合，使用光物理方法产生和询问活性金属中心。实验方法：最近，稳定的SMOM系统的设计主题已经确定。在这些标准的指导下，将合成新的阳离子锰或重-羰基配合物，并研究它们在固体中的反应活性。[M(络合配体)(CO)n][BArF4]。各种各样的配基基序(螯合物、钳形、非无辜配体)将被用来生成一个新的第7族SMOM系统的文库。它们可能已经是配位不饱和的(无配位的)，或者，唯一的，可以通过光解的CO损失在原位激活。这些化合物本身就是令人着迷的络合物，它们是高活性的16或14电子物种，为固/气过程中的反应做好了准备，也是传统溶液过程的催化剂。除了这些体系中的基本结构键外，还有许多反应性可以探索，例如烷烃、氢气和惰性气体络合物、C-H活化和固/气催化(例如加氢、醇的脱氢、异构化)。它还为使用时间分辨红外光谱学研究固态中的事件提供了机会(莱纳姆是该领域的专家)。新颖性：7族络合物的固态分子化学及其光物理性质的研究是新颖的；并将导致高影响力的出版物。它将突破SMOM化学中可实现的界限，开发新的化学(SMOM-PhotoChem)，并可能解锁新的催化系统。培养：博士生将成为金属有机合成、核磁共振(溶液和固态)、X射线结晶学和新的光物理技术方面的专家。探索固体/气体催化的机会将会很多。

Background: Organometallic synthesis, reactivity and catalysis is nearly always performed in the solution phase, where the complex, or catalyst, of interest is dissolved in a solvent of choice. While this is convenient it often means that very reactive intermediates in catalysis, or complexes in synthesis, are challenging to observe, let alone isolate, as the solvent often binds, or irreversibly reacts, with the metal centre. The Weller group has recently developed a technique to avoid solvent binding, and thus isolate, characterise and study highly reactive complexes that cannot be made by traditional solution routes. The technique is deceptively simple: all the chemistry, characterisation, reactivity and even catalysis is carried out in single-crystal to single-crystal transformations in which gases penetrate the crystal and react with the metal centre to generate the target complex, or undergo the catalytic transformation of interest. We term this solid-state molecular organometallic chemistry (SMOM-Chem). For example this approach allows for cationic sigma-alkane complexes to be synthesised, key - but normally transient - intermediates in C-H activation process. A stabilising "nanoreactor" of [BArF4]- anions around a reactive cation in the crystal lattice (similar to enzyme reactive sites) is key to this. The power of this approach is demonstrated by the synthesis on gram scale of such alkane complexes that are indefinitely stable at room temperature, whereas in solution lifetimes are (at best) minutes at temperatures of -100 degrees C and mg quantities. SMOM techniques thus allow for the isolation of "impossible" complexes.Objectives: Up until now this chemistry has focussed on group 9 complexes. The question is can SMOM chemistry be extended to other transition metals, and can very reactive, synthetically challenging, and catalytically interesting, systems be developed? We will answer this in an exciting new project that combines SMOM techniques with group 7 cations (Mn, Re) using photophysical methods to generate and interrogate the reactive metal centres. Experimental Approach: Very recently the design motifs for stable SMOM systems has been determined. Informed by these criteria new cationic Mn- or Re-carbonyl complexes will be synthesised and their reactivity studied in the solid-state, e.g. [M(chelating-ligand)(CO)n][BArF4]. A wide variety of ligand motifs (chelate, pincer, non-innocent ligands) will be used to generate a library of new group-7 SMOM systems. These may already be coordinatively unsaturated (agostic) or, uniquely, can be activated in situ by CO-loss using photolysis. These will be fascinating complexes in their own right, being highly reactive 16 or 14-electron species that are primed for reactivity in solid/gas processes, as well as "drop-in" catalysts for traditional solution processes. In addition to the fundamental structure bonding in these systems there is much reactivity to explore, e.g. alkane, H2 and noble-gas complexes, C-H activation and solid/gas catalysis (e.g. hydrogenation, dehydrogenation of alcohols, isomerisation). It also opens the opportunity to study events within the solid-state using time-resolved infra-red spectroscopy (Lynam is an expert in the area). Novelty: The study of solid-state molecular chemistry of group-7 complexes, and their photophysical properties, is novel; and will result in high-impact publications. It will push the boundaries of what is achievable in SMOM chemistry, develop new chemistry (SMOM-photochem) and potentially unlock new catalytic systems. It takes 3d-metal chemistry in a new direction.Training: The PhD student will become expert in organometallic synthesis, NMR (solution and solid-state), x-ray crystallography and new photophysical techniques. There will be plenty of opportunities to explore solid/gas catalysis.