CAS: Pincer Ligand Base Metal Chromophores for Selective Free Radical Reactions

在该项目中，由化学部化学结构、动力学机制B计划资助，格鲁吉亚理工学院化学与生物化学学院的Jake Soper正在开发新型过渡金属催化剂，该催化剂能够利用可见光将芳基碳-氢键转化为碳-（三氟）烷基键，碳-（三氟）烷基键是许多农用化学品和药物的重要组成部分。这项研究的目标是设计新的地球丰富的金属络合物，可以取代基于贵金属的光催化剂，并制定新的方法来选择性地针对单个碳-氢键进行自由基活化和功能化。通过用天然丰富的替代品取代稀有和有毒的金属催化剂和化学计量的、通常含卤素的氧化剂，该项目为保护人类健康和环境的制药和材料的新“绿色”路线奠定了基础。为了实现这些目标，该项目还为高中STEM教育工作者的发展提供了机会，并为传统上在化学领域代表性不足的群体提供了提高公众参与和科学素养的外展活动。基于第一行过渡金属的光氧化还原活性发色团的制备工作受到短电荷转移激发态寿命的挑战，这会妨碍光氧化还原反应性。该项目的研究提出通过将发色团和有机金属反应中心结合在单个配位络合物中来规避这个问题，开辟了新的途径来赋予通过动力学上容易的自由基步骤发生的光氧化还原催化循环的选择性。该策略的核心是新钳形络合物支持光解钴键活化的能力，从而导致碳基自由基的挤出，所述碳基自由基对（杂）芳烃的烷基化、氟烷基化和芳基化具有活性。底物导向基团被提议将这些自由基引导到特定的芳基碳氢键上，从而在光化学Minisci型均裂芳族取代中产生非典型的区域选择性。该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估来支持。

In this project, funded by the Chemical Structure, Dynamics & Mechanism B Program of the Chemistry Division, Jake Soper of the School of Chemistry and Biochemistry at the Georgia Institute of Technology is developing new transition metal catalysts capable of using visible light to convert aryl carbon–hydrogen bonds into carbon–(trifluoro)alkyl bonds, which are important components of many agrochemicals and pharmaceuticals. The goals of this research are to design new earth-abundant metal complexes that can replace photocatalysts based on precious metals and to elaborate new ways to selectively target individual carbon–hydrogen bonds for radical activation and functionalization. By replacing rare and toxic metal catalysts and stoichiometric, often halogen-containing, oxidants with naturally abundant alternatives, the project forms the basis for new "green" routes to pharmaceutical and materials that protect human health and the environment. In pursuit of these goals, the project also affords opportunities for high school STEM educator development, as well as outreach activities that increase public engagement and science literacy among groups that are traditionally underrepresented in chemistry.Efforts to elaborate photoredox-active chromophores based on first row transition metals are challenged by short charge-transfer excited-state lifetimes that preclude bimetallic reactivity. Research in this project proposes to circumvent this issue by combining the chromophore and organometallic reaction center in single coordination complex, opening new avenues to impart selectivity in photoredox catalysis cycles that occur via kinetically facile radical steps. Central to this strategy is the capacity of new pincer complexes to support photolytic cobalt bond activation leading to extrusion of carbon based radicals, which are active for alkylation, fluoroalkylation, and arylation of (hetero)arenes. Substrate directing groups are proposed to shepherd these radicals to specific aryl carbon hydrogen bonds, giving atypical regioselectivity in photochemical Minisci-type homolytic aromatic substitution.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.