Mechanistic Role of Additives and Solvent in Sm(II)-Based Reactions

添加剂和溶剂在 Sm(II) 基反应中的机理作用

• 批准号: 0844946
• 负责人: Robert Flowers
• 金额: $ 39万
• 依托单位: Lehigh University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-03-01 至 2013-02-28
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0844946&HistoricalAwards=false
• 关键词: Mechanistic; Role; Additives; Solvent; Sm

Samarium diiodide (SmI2) and other Sm(II)-based reductants provide unique reagents for a variety of important synthetic transformations. One of the distinctive features of Sm(II)-based reductants is that their reactivity can be drastically altered by changing the solvent or by adding cosolvents or other additives. Although great strides have been achieved in the use of Sm(II) reagents in organic synthesis, the role of solvent and additives in reactions is poorly understood, and, as a result, the full potential of these reductant-additive combinations has not been realized. This work is directed towards understanding the relationship between solvent and additives and their effect on the rates and selectivities of Sm(II)-mediated functional group conversions through two discrete mechanistic studies.The first study will define the relationship between the affinity of solvents, proton donors, and coordinating or chelating additives for Sm(II) reagents and the relationship of these variables to the reactivity of Sm(II). This work will establish the degree to which coordinating solvents attenuate the reactivity of Sm(II) through interaction with substrates and commonly utilized additives providing chemists with important mechanistic data comparing the reactivity of Sm(II)-cosolvent complexes in a range of solvents in which they are commonly used. Overall, the goal of this portion of the work is to address the effects of solvation at the molecular level through the treatment of solvent as a high molarity ligand, not a medium of fixed dielectric constant. The second study addresses the mechanistic function of Ni diiodide and other transition metal salts on Sm(II)-mediated reductions. The impact of catalytic Ni diiodide and other Ni(II) salts on a range of reactions of SmI2 will be critically examined through a series of mechanistic studies employing stopped-flow spectrophotometry and reaction calorimetry. Mechanistic studies of reactions providing evidence for Ni(0)-based chemistry will be further investigated using reaction progress kinetic analysis. As these studies proceed, the intermediacy of Ni(0) nanoparticles will be examined to distinguish homogeneity from colloid-based chemistry. The broad goal of this work is designed to provide a mechanistic understanding of Sm(II)-based chemistry that can be extrapolated and applied to a range of important and useful processes. Studies utilizing this approach are likely to provide longer term benefits to the scientific community than simply the demonstration of a single synthetic application. The work contained in this proposal will also provide important professional preparation for graduate and undergraduate students in the mechanistic study, use, and applications of a reagent that is becoming increasingly important in organic synthesis. Students will receive training in the use and application of a range of useful techniques not typically used in standard organic laboratories and therefore the breadth of tools used in this project will provide unique training and perspective to organic students. Inclusion of undergraduate students from the Lehigh advanced laboratory course sequence in the mechanistic study and development of reactions employing the SmI2/catalytic Ni diiodide system will provide important training not typically acquired in a traditional undergraduate laboratory course.

二碘化钐（SmI2）和其他Sm（II）基还原剂为各种重要的合成转化提供了独特的试剂。Sm（II）基还原剂的一个显著特征是它们的反应性可以通过改变溶剂或添加助溶剂或其他添加剂而急剧改变。虽然Sm（II）试剂在有机合成中的应用已经取得了很大的进步，但人们对溶剂和添加剂在反应中的作用知之甚少，因此，这些还原剂-添加剂组合的全部潜力尚未实现。这项工作旨在通过两个离散的机制研究，了解溶剂和添加剂之间的关系，以及它们对Sm（II）介导的官能团转化速率和选择性的影响。第一项研究将确定溶剂、质子供体和配位或螯合添加剂对Sm（II）试剂的亲和力之间的关系，以及这些变量与Sm（II）反应性的关系。这项工作将确定配合溶剂通过与底物和常用添加剂的相互作用减弱Sm（II）反应性的程度，为化学家提供重要的机制数据，比较Sm(II)-共溶剂配合物在一系列常用溶剂中的反应性。总的来说，这部分工作的目标是通过将溶剂作为高摩尔浓度的配体处理，而不是固定介电常数的介质，在分子水平上解决溶剂化的影响。第二项研究解决了二碘化镍和其他过渡金属盐在Sm（II）介导还原中的机制功能。催化二碘化镍和其他Ni（II）盐对一系列SmI2反应的影响将通过采用停流分光光度法和反应量热法的一系列机理研究进行严格检查。为Ni(0)基化学提供证据的反应机理研究将进一步利用反应过程动力学分析进行研究。随着这些研究的进行，Ni(0)纳米颗粒的中间作用将被检查，以区分胶体基化学的均匀性。这项工作的广泛目标是提供一个基于Sm（II）的化学的机制理解，可以外推并应用于一系列重要和有用的过程。利用这种方法进行的研究可能会给科学界带来长期的好处，而不仅仅是演示单一的综合应用。本提案所包含的工作也将为研究生和本科生在有机合成中越来越重要的试剂的机理研究、使用和应用方面提供重要的专业准备。学生将接受使用和应用一系列在标准有机实验室中通常不使用的有用技术的培训，因此本项目中使用的工具的广度将为有机学生提供独特的培训和视角。招收理哈伊大学高级实验课程的本科生参与SmI2/催化二碘化镍体系反应的机理研究和发展，将提供传统本科实验课程通常无法获得的重要训练。