SusChEM: Molecular Information and Crystal Control in Solid State Photochemical Reactivity

在化学系化学结构、动力学机制B项目的资助下，Miguel A.加州大学洛杉矶分校化学与生物化学系的Garcia-Garibay正在建立新的合成策略，通过利用在结晶状态的高度有序和刚性下发生的反应，将简单的化学物质转化为更复杂，更高价值的物质。 他们的策略依赖于选择已知在被紫外光吸收激活时形成高活性中间体的结构。 通过在结晶状态下进行这些反应，而不是在液体中进行，它们能够获得几乎纯的固体产物，而不需要溶剂，催化剂或其他试剂。该项目属于SusChEM产品组合，因为反应不使用溶剂，不需要能量来分离和去除副产物。 该项目为多名学生提供了一个良好的多学科培训基地。 研究生和暑期本科生从三个合作的历史上黑人学院和大学机构：霍华德大学，克拉克亚特兰大大学和斯佩尔曼学院，参与。 在实施了强有力的策略，通过选择产生高活性中间体的稳定分子来设计晶体中的反应后，该项目解决了六取代酮的固态光脱羰基和三唑啉，吡唑啉和选定的芳香族叠氮化物的光脱氮。 自由基对，biradigradicals，和氮烯在结晶状态下产生的反应物的激发态的高度放热过程中，和他们的产品的形成和动力学进行了详细分析。在固体状态下，自由基-自由基组合反应保留立体化学，并发生选择性氮烯插入。 光化学反应在充分表征的结晶相中进行，并且通过热分析和光谱手段分析它们从反应物的固相到产物的固相的转化。 进行这种表征是为了确定相应的相图和清洁和有效反应所需的条件。 详细的反应机制进行了探讨，利用单晶X-射线衍射和动力学测量获得的激光闪光光解测量使用纳米晶体悬浮在水中的结构信息。

With funding from the Chemical Structure, Dynamics & Mechanisms B Program of the Chemistry Division, Professor Miguel A. Garcia-Garibay of the Department of Chemistry and Biochemistry at the University of California-Los Angeles is establishing new synthetic strategies to transform simple chemicals into more complex, high value substances, by taking advantage of reactions that occur under the high order and rigidity of the crystalline state. Their strategy relies on the selection of structures that are known to form highly reactive intermediates when activated by the absorption of ultraviolet light. By executing those reactions in the crystalline state, instead of doing them in liquids, they are able to obtain nearly pure solid products with no need for solvents, catalysts or additional reagents. This project is in the SusChEM portfolio as the reactions do not use solvent and require no energy for the separation and removal of byproducts. This project provides an excellent multidisciplinary training ground for several students. Graduate students and summer undergraduates from three partnering Historically Black Colleges and Universities institutions: Howard University, Clark Atlanta University, and Spellman College, are involved. Having implemented robust strategies to engineer reactions in crystals by selecting stable molecules that generate highly reactive intermediates, this project addresses the solid state photodecarbonylation of hexasubstituted ketones and the photodenitrogenation of triazolines, pyrazolines, and selected aromatic azides. Radical pairs, biradicals, and nitrenes are generated in the crystalline state in highly exothermic processes from the excited state of the reactants, and their product formation and kinetics are analyzed in detail. In the solid state, radical-radical combination reactions with retention of stereochemistry, and selective nitrene insertions occur. Photochemical reactions are carried out in well-characterized crystalline phases and their transformations from the solid phase of the reactant to the solid phase of the product are analyzed by thermal analysis and spectroscopic means. This characterization is done in order to determine the corresponding phase diagrams and the conditions required for clean and efficient reactions. Detailed reaction mechanisms are explored by taking advantage of structural information available from single crystals X-ray diffraction and kinetic measurements obtained from laser flash photolysis measurements using nanocrystals suspended in water.