The Influence of Dynamic Coordination Spheres in Metal-Based Homogeneous Catalysis

支持配体在控制金属络合物的催化功效中的作用不能被夸大。开发能够有效稳定催化中间体的高齿数配体与留下用于底物结合的空配位位点的低配位数之间的平衡可能是具有挑战性的。我们最近发现，主族金属的催化效率可以通过使用高齿数配体，通过利用这些封闭的壳层金属离子的固有的不稳定性增加。这种催化剂设计策略的例子是铝催化的异氰酸酯与5-配位配体，其中包含半不稳定的吡啶供体的三聚反应。吡啶基能够去配位，并且通过这样做不利于将导致较慢的反应动力学的逆反应;这种催化剂比其无吡啶基的对应物活性高得多。本项目的目的是探索其他主族金属和其他催化转化的影响范围。这些金属预计将覆盖第13族，但也可能延伸到s区块和早期d区块。我们还设想在聚合和共聚反应中探测该反应的有效性。预计聚合反应主要集中在环氧化物/酸酐共聚物上，其含有酯键，因此是可生物降解/可水解的。有超过100，000种不同的单体组合，这意味着它们可以比传统聚合物具有更大的性能范围;例如，我们已经制备了不含有毒添加剂的阻燃衍生物。大多数共聚合催化剂基于Salen型配体;缺乏对替代配体环境的广泛研究是进一步开发这些共聚物的固有限制。我们特别感兴趣的是确定是否可以利用动态配位球来提高制备交替共聚物的效率。虽然聚合仍然是主要焦点，在其它小分子如H2和CO的活化中，存在探索表现出动力学配位行为的络合物的影响的范围，所述其它小分子导致氢化和/或还原。新的配体先导物和络合物将从初始研究中获得，并不断地为后续研究提供信息。

The role of supporting ligands in controlling the catalytic efficacy of metal complexes cannot be overstated. A balance between developing high denticity ligands that are able to effectively stabilise catalytic intermediates, and low coordination numbers that leave vacant coordination sites for substrate binding, can be challenging. We have recently discovered that the catalytic efficacy of main group metals can be increased by employing high denticity ligands by exploiting the inherent lability of these closed shell metal ions.This catalyst design strategy is exemplified by the aluminium-catalysed trimerization of isocyanates with a 5-coordinate ligand that contains a hemi-labile pyridyl donor. The pyridyl is able to de-coordinate, and by so doing disfavours the backwards reaction that would lead to slower reaction kinetics; this catalyst is much more active than its pyridyl-free counterpart. The aim of this project is to probe the scope of this effect with other main group metals, and with other catalytic transformations. These metals are expected to cover Group 13 but could also extend into the s-block and early d block. We also envisage probing the effectiveness for this reaction in polymerisation and co-polymerisation reactions. Polymerisation reactions are expected to focus primarily on epoxide/anhydride co-polymers, which contain ester linkages and are therefore biodegradable / hydrolysable. There are > 100,000 different monomer combinations, which means that they can be prepared with greater property scope than traditional polymers; for example, we have prepared flame-retardant derivatives with no toxic additives. Most co-polymerisation catalysts are based upon salen-type ligands; the lack of extensive studies with alternative ligand environments is an inherent limitation to further exploitation of these co-polymers. We are particularly interested to determine if a dynamic coordination sphere could be exploited to increase efficiency in preparing alternating co-polymers.While polymerisation remains the primary focus, there is scope for exploring the influence of complexes exhibiting dyanamic coordination behaviour in the activation of other small molecules such as H2 and CO which leads into hydrogenation and/or carbonylation catalysis.New ligand leads and complexes will derive from initial studies and continually inform subsequent studies.