Comparative Nucleophilic Displacement Reactions at Phosphorus and Silicon

该奖项在无机，生物无机和有机化学 该计划为罗伯特·R博士提供持续支持。福尔摩斯 化学系，马萨诸塞州阿默斯特大学，为 磷和硅化合物反应性的研究。 期间 取代反应，磷和硅容纳五个或六个 围绕着中心原子。 这种类型的高活性物质 将合成，使用NMR光谱表征，并建模 使用从头算方法和圣地亚哥的能力， 超级计算机中心。 环五氧正膦和等电子 五配位阴离子硅酸盐将是研究的焦点。 具有不同大小的环和各种供体原子的取代基 会做好准备。 磷的工作预计将提供信息， 环磷酸腺苷（cAMP）的水解机制， 而硅工作模拟了硅烷醇的初始阶段， 聚合法 在这两种情况下，目标都是探索 六配位中间体作为增加反应性的来源 观察到五配位磷和硅化合物。 的 较高配位的水解和溶剂分解的反应速率 衍生物将被确定并与较低的衍生物进行比较。 协调物种 将使用氮供体原子以模拟 存在于酶活性位点的氨基酸残基的功能 并评估它们在形成更高配位中间体中的作用。 这项研究将确定替代反应途径在 两个重要案例。 六配位中间体的可能性 影响生理学上重要的 磷酰基转移反应或在商业上重要的 以前没有研究过硅烷醇的聚合。

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.