Comparative Nucleophilic Displacement Reactions at Phosphorus and Silicon

这一无机化学、生物无机化学和金属有机化学项目的奖项为马萨诸塞大学阿默斯特分校化学系的Robert R.Holmes博士提供了持续的支持，以表彰他对磷和硅化合物的反应性的研究。在取代反应中，磷和硅在中心原子周围容纳了五到六个基团。这种类型的高活性物种将被合成，使用核磁共振光谱进行表征，并使用从头计算方法和圣地亚哥超级计算机中心的能力进行建模。环状五氧基磷烷和等电子五配位阴离子硅酸盐将是研究的重点。将制备具有不同大小的环和各种给体原子的取代基。磷的工作预计将提供环腺苷一磷酸(CAMP)的水解机理的信息，而硅的工作将模拟硅醇聚合的初始阶段。在这两种情况下，目标都是探索六配位中间体的形成，作为观察到的五配位磷和硅化合物反应性增加的来源。将测定高配位衍生物的水解和溶解反应速率，并与低配位物种的反应速率进行比较。氮供体原子将被用来模拟存在于酶活性部位的氨基酸残基的功能，并评估它们在形成更高配位中间体方面的作用。这项研究将确定替代反应途径在两个重要案例中的作用。在生理上重要的磷酰基转移反应或在重要的商业意义上的硅醇聚合中，六配位中间体影响反应性和几何构型的可能性以前还没有被探索过。

This award in the Inorganic, Bioinorganic, and Organometallic Chemistry Program provides continued support to Dr. Robert R. Holmes of the Chemistry Dearptment, University of Massachusetts at Amherst, for research on the reactivity of phosphorus and silicon compounds. During substitution reactions, phosphorus and silicon accommodate five or six groups around the central atom. Highly reactive species of this type will be synthesized, characterized using NMR spectroscopy, and modeled using ab initio methods and the capabilities of the San Diego supercomputer Center. Cyclic pentaoxyphosphoranes and isoelectronic five-coordinate anionic silicates will be the focus of the investigation. Substituents with rings of varying sizes and a variety of donor atoms will be prepared. The phosphorus work is expected to give information on the mechanism of hydrolysis of cyclic adenosine monophosphate, cAMP, while the silicon work models the initial stages of silanol polymerization. In both cases, the goal is to explore the formation of six-coordinate intermediates as the source of the increased reactivity observed for five-coordinate phosphorus and silicon compounds. The reaction rates for hydrolysis and solvolysis of the higher coordinate derivatives will be determined and compared to those of the lower coordinate species. Nitrogen donor atoms will be used in order to mimic the functions of amino acid residues present at the enzymatic active site and assess their role in forming higher coordinate intermediates. This research will determine the role of an alternate reaction pathway in two important cases. The possibility of six-coordinate intermediates affecting both reactivity and geometry in the physiologically important reaction of phosphoryl transfer or in the commercially important polymerization of silanol has not been previously explored.