Comparative Nucleophilic Displacement Reactions at Phosphorus and Silicon

这个无机、生物无机和有机金属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博士对磷和硅化合物的反应性的研究提供了持续的支持。在取代反应中，磷和硅在中心原子周围容纳5或6个基团。这种类型的高活性物质将被合成，使用核磁共振光谱进行表征，并使用从头算方法和圣地亚哥超级计算机中心的能力进行建模。环五氧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环和各种给体原子的取代基。磷功有望提供有关环磷酸腺苷（cAMP）水解机理的信息，而硅功模拟了硅醇聚合的初始阶段。在这两种情况下，目标是探索六坐标中间体的形成，作为五坐标磷和硅化合物观察到的反应性增加的来源。将测定高配位衍生物的水解和溶剂溶解反应速率，并与低配位衍生物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位点的氨基酸残基的功能，并评估它们在形成高配位中间体中的作用。本研究将确定在两个重要案例中替代反应途径的作用。在生理上重要的磷酰转移反应或商业上重要的硅醇聚合反应中，六坐标中间体影响反应性和几何形状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.