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

支持配体在控制金属络合物催化效率方面的作用怎么强调都不为过。在开发能够有效稳定催化中间体的高密度配体和为底物结合留下空置配位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，通过利用闭壳金属离子固有的不稳定性，使用高密度配体可以提高主要族金属的催化效率。这种催化剂设计策略以铝催化的异氰酸酯与含有半不稳定的吡啶供体的五配位配体的三聚为例。吡啶能够脱配，这样做不利于反向反应，从而导致反应动力学变慢；这种催化剂比不含吡啶的催化剂活性高得多。这个项目的目的是探索这种影响的范围与其他主要族金属，以及其他催化转化。这些金属预计将覆盖第13组，但也可能延伸到S区块和早期d区块。我们还设想探索这种反应在聚合和共聚反应中的有效性。聚合反应预计将主要集中在环氧化物/酸酐共聚物上，这种聚合物含有酯键，因此是可生物降解/可水解的。有100,000种不同的单体组合，这意味着它们可以制备出比传统聚合物更大的性能范围；例如，我们制备了不含有毒添加剂的阻燃衍生物。大多数共聚催化剂是基于Salen型配体的；缺乏对替代配体环境的广泛研究是进一步开发这些共聚聚合物的固有限制。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的焦点，但仍有空间探索表现出动态配位行为的配合物在其他小分子如H2和CO的活化中的影响，从而导致氢化和/或羰化催化。新的配体先导和配合物将从初步研究中衍生出来，并继续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.