Pushing the Boundaries of Supraicosahedral Heteroborane Chemistry: New Supraicosahedral Carboranes and Metallacarboranes

这项研究涉及到大团簇分子的制备，主要是硼原子，但也包括碳和金属原子。硼的团簇化学主要由团簇/二十面体/中只有12个原子的分子所主导，其中有成千上万个已知的例子。相比之下，可能只有不到200个这样的星团有13个原子，只有少数几个有14个原子，直到最近，还没有15个原子的星团，也没有更大的。这是不幸的，因为如果能制造出更大的化合物，特别是如果能加入更多的硼原子，这种簇合物的几个实际和潜在的应用将得到加强，包括它们在催化和肿瘤治疗中的应用。制备这些大型超二十面体硼簇合物的最大障碍是，一旦你超出了二十面体，团簇中的原子必须与他们的邻居建立更多的键，而不是他们可以轻松做到的。然而，以前的理论工作表明，这可能只对13、14和15个顶点的化合物来说是一个问题，并且对于那些具有16个或更多顶点的簇合物，可以采用避免这个问题的形状。拟议工作的主要目标之一是试图达到16个顶点和更多(我们目前只有一个顶点)，看看实际发生了什么。我们制造超二十面体分子的方法是一种被称为多面体扩展的技术，这是一个两步的过程，我们首先通过增加2个电子来打开原子团，然后添加额外的原子来隐藏笼子。尽管硼在二十面体以上的团簇中形成许多键是不舒服的，但我们仍然可以通过添加过渡金属原子而不是硼来制备和研究此类化合物，因为金属比硼大得多。因此，我们打算的策略的一部分，是故意使用过渡金属顶点来更多地了解这些不寻常的分子，并帮助我们找到最终制造与硼相同的化合物的方法。折中方案是使用介于硼和过渡金属之间的主族金属，我们也建议在这一领域进行研究。大部分计划的工作涉及准备新的团簇和确定其结构。但此外，我们还计划对这一领域的各个方面进行计算研究，最终希望能够建立一套工作规则，既帮助我们回溯理解实验结果，也帮助我们建立有用的协议，指导未来的实验工作。

This research is concerned with the preparation of large cluster molecules, mainly of boron atoms but also carbon and metal atoms as well. Boron cluster chemistry is dominated by molecules with only 12 atoms in the cluster / the icosahedron / of which there are thousands of known examples. In contrast there are probably less than 200 such clusters with 13 atoms, only a handful with 14 atoms, and, until very recently, no such clusters with 15 atoms, and nothing larger. This is unfortunate as several of the actual and potential applications of such clusters, including their use in catalysis and in tumour therapy, would be enhanced if larger compounds could be made, particularly if more boron atoms could be incorporated.The biggest obstacle to the preparation of these large supraicosahedral boron clusters is that once you get beyond the icosahedron the atoms in the cluster have to make more bonds to their neighbours than they can comfortably do. However, previous theoretical work has suggested that this may only be an issue for 13, 14 and 15-vertex compounds, and that for those clusters with 16 or more vertices, shapes can be adopted which avoid this problem. One of the major aims of the proposed work is to try to get to 16 vertices and beyond (we are currently only one vertex away from this) to see what actually happens.The way we will make the supraicosahedral molecules is by a technique know as polyhedral expansion , a two step process in which we first open up the cluster by adding 2 electrons then add the additional atom to recluse the cage. Even though boron is uncomfortable in making many bonds in supraicosahedral clusters we can still prepare and study such compounds by adding transition metal atoms instead of boron, because metals are significantly larger than boron. Part of our intended strategy, then, is deliberately to use transition metal vertices to learn more about these unusual molecules, and to help us discover ways to ultimately make the same compounds with boron. A halfway-house would be to use main group metals, which have characteristics between those of boron and transition metals, and we also propose to research in this area.Most of the planned work is concerned with preparing new clusters and determining their structures. But in addition we are also planning to study aspects of this area computationally, with the ultimate hope of being able to establish a set of working rules, both to help us understand the experimental results retrospectively and to help us establish useful protocols that will guide future experimental work.