Comparative Nucleophilic Displacement Reactions at Phorphorus and Silicon

在这个由无机化学、生物无机化学和金属有机化学计划资助的项目中，马萨诸塞大学的罗伯特·R·霍姆斯将研究磷和硅的亲核置换反应被描述为共同基础的程度。这些元素的取代反应机理的研究涉及到生物过程中的磷酰基转移反应以及硅醇和硅酸盐聚合生成硅酸盐和硅酮等一系列相关问题。这个问题将通过实验和理论相结合的方法来研究，这将导致确定这些过程中可能的中间体的能量学和立体化学。该理论程序包括从头算分子轨道计算，并将处理一系列进入、离开和不离开基团的常见亲核置换反应。实验项目包括五配位阴离子硅酸盐的合成和结构表征，如五(烷氧基)、五(羟基)和五卤代硅酸盐，以及混合的烷基卤代、烷氧基羟基和氯氟五氟硅酸盐。将进行单晶X射线结构分析和固体核磁共振测量，以确定固体和溶液之间的结构变化，并评估配体交换过程的激活能。

In this project funded within the Inorganic, Bioinorganic and Organometallic Chemistry Program, Robert R. Holmes of the University of Massachusetts will investigate the extent to which phosphorus and silicon nucleophilic displacement reactions are described by a common basis. The study of the substitution reaction mechanisms of these elements relates to a wide range of relevant problems such as phosphoryl transfer reactions in biological processes and the polymerization of silanols and siliconates to form silicates and silicones. The problem will be studied by a combined experimental and theoretical approach which leads to the determination of the energetics and stereochemistry of the likely intermediates in these processes. The theoretical program consists of ab-initio molecular orbital calculations and will treat common nucleophilic displacement reactions for which a series of entering, leaving and non-departing groups are varied. The experimental program involves the synthesis and structural characterization of five-coordinated anionic siliconates such as penta(alkoxy)- ,penta(hydroxy)- and pentahalo-siliconates as well as mixed alkylhalo-, alkoxyhydroxy- and chlorofluoro- penta-substituted siliconates. Single crystal X-ray structural analysis and solid state nuclear magnetic resonance measurements will be conducted to determine structural change between the solid and solution states and to evaluate activation energies for ligand exchange processes.