Exploring alternative phosphorus and heavier pnictogen feedstocks for bespoke chemical transformations

过渡金属和主族元素配合物对白磷的化学活化历来被认为是一种避免使用三氯化磷作为化学原料的方法。尽管氯化磷具有毒性（其使用目前受《禁止化学武器公约》管制），但它仍然是我们日常在洗涤剂、药品和特种化学品中遇到的所有有机磷化合物的主要p原子来源。目前，由于现有的技术投资和成本问题，采用替代方法生产散装含磷化学商品是不可行的。然而，从经济和健康安全的角度来看，使用替代原料合成增值特种化学品是非常有吸引力的。白磷的直接化学活化是制备有机磷化合物的可行途径；不幸的是，这种转换通常表现出低选择性和/或需要多次后续操作才能与工业过程竞争。此外，白磷本身是高度易燃的，是一种危险的物质（在历史上众所周知，它被用作化学武器）。尽管如此，在过去的四十年里，白磷的化学活化已经产生了一个令人难以置信的丰富和多样化的基础化学领域（“磷有机”和“无机金属”化学等领域因此而蓬勃发展），使科学界能够发展出变革性的概念，这些概念在从超分子化学到催化等领域都产生了影响。我们建议研究15族元素（P, As, Sb, Bi）的替代原料来合成新的有机烟原化合物。我们研究小组的初步概念验证结果表明，碱金属和第15族元素的二元Zintl相可以用作合成含有烟草原类似物的有机配体的新物种的起始材料（这些转化与金属介导的白磷活化过程密切相关）。此外，我们还证明了使用这些物质直接化学激活小分子（如炔烃）是可能的。值得注意的是，这些盐状的Zintl相前体可以使用15族元素（红磷、金属灰砷）的更安全的同素异形体来获取，从而避免了与操纵白磷或黄砷相关的风险。这使得操纵这些物质的危险性大大降低，减少了在操纵更传统的原料时通常遇到的健康和安全风险（虽然Zintl相仍然对空气和湿度敏感，但它们与空气接触时不会自燃）。我们建议研究Zintl相对一系列低价过渡金属和小分子试剂的反应性，以合成其他难以获得的“pnico -organic”分子物种。我们对这类化合物的策略集中在两种互补的合成方法上：1)用低价过渡金属配合物激活阴离子肽笼；2)聚阴离子与不饱和小分子底物的直接反应。最终，我们相信这些研究将产生新的15族元素分子物种，这些元素可以直接或作为辅助配体用于化学计量和催化键激活过程，或作为新材料的前体。

The chemical activation of white phosphorus by transition-metal and main-group element complexes has historically been heralded as a way of circumventing the use of phosphorus trichloride as a chemical feedstock. Despite its toxic nature (and the fact that its use is currently regulated under the Chemical Weapons Convention), phosphorus (III) chloride remains the principal P-atom source for all of the organophosphorus compounds we encounter on a daily basis in detergents, pharmaceuticals and specialty chemicals. At present, pre-existing technological investment and cost issues make it unfeasible to employ alternative methods for the production of bulk phosphorus-containing chemical commodities. However, the use of alternate feedstocks for the synthesis of value-added specialty chemicals is very attractive both financially and from a health and safety perspective. The direct chemical activation of white phosphorus is demonstrably a viable route to organophosphorus compounds; unfortunately such transformations typically exhibit low selectivities and/or require multiple subsequent manipulations to be competitive with industrial processes. Furthermore, white phosphorus is itself highly pyrophoric and a dangerous substance to manipulate (notoriously used throughout history as a chemical weapon). Nonetheless, throughout the last forty years the chemical activation of white phosphorus has generated an incredibly rich and diverse area of fundamental chemistry (fields such "phospha-organic" and "inorganometallic" chemistry have blossomed as a result) allowing the scientific community to develop transformative concepts that have had repercussions in fields ranging from supra-molecular chemistry to catalysis.We propose to investigate alternative group 15 element (P, As, Sb, Bi) feedstocks for the synthesis of novel organo-pnictogen compounds. Preliminary proof-of-concept findings by our research group have demonstrated that binary Zintl phases of the alkali metals and group 15 elements may be used as starting materials for the synthesis of novel species containing pnictogen analogues of organic ligands (these transformations are closely related to metal-mediated processes for the activation of white phosphorus). Moreover, we have also shown it is possible to use such species for the direct chemical activation of small molecules such as alkynes. It is important to note that these salt-like Zintl phase precursors can be accessed using safer allotropes of the group 15 elements (red phosphorus, metallic grey arsenic), thus avoiding the risks associated with the manipulation white phosphorus or yellow arsenic. This makes the manipulation of such species notably less dangerous, reducing the health and safety risks typically encountered when manipulating more traditional feedstocks (while Zintl phases are still air- and moisture-sensitive they are do not spontaneously combust on contact with air). We propose to investigate the reactivity of Zintl phases towards a library of low-valent transition-metal and small molecule reagents with the aim of synthesizing otherwise unattainable "pnicto-organic" molecular species. Our strategy towards such compounds centres on two complimentary synthetic methodologies: 1) the metal-mediated activation of anionic pnictide cages with low-valent transition-metal complexes; and 2) the direct reaction of pnictide polyanions with unsaturated small molecule substrates. Ultimately, we believe such studies will give rise to novel molecular species of the group 15 elements that may be used - directly or as supporting ligands - in stoichiometric and catalytic bond activation processes or as precursors to novel materials.