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

在这个由化学部化学结构、动力学和机理B计划资助的项目中，佐治亚理工学院化学和生物化学学院的杰克·索珀正在开发能够利用可见光将芳基碳氢键转化为碳(三氟)烷基的新型过渡金属催化剂，这是许多农用化学品和制药的重要组成部分。这项研究的目标是设计新的富含地球的金属络合物，以取代基于贵金属的光催化剂，并阐述选择性地针对单个碳氢键进行自由基活化和功能化的新方法。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氧化剂(通常含有卤素)，该项目为获得保护人类健康和环境的制药和材料的新的“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教育者的发展提供了机会，以及增加公众参与和在传统上在化学中代表不足的群体中的科学素养的外联活动。基于第一行过渡金属的精细光氧化还原活性发色团的努力受到了短的电荷转移激发态寿命的挑战，这阻止了双金属的反应。该项目的研究建议通过将发色团和有机金属反应中心结合在单一配位络合物中来规避这一问题，从而开辟了在光氧化还原催化循环中提供选择性的新途径，这些循环通过动力学上容易实现的自由基步骤发生。这一策略的核心是新的钳形络合物能够支持光解钴键的激活，导致碳基自由基的挤出，这些自由基对(杂环)芳烃的烷基化、氟烷基化和芳基化具有活性。底物导向基团被建议引导这些自由基到特定的芳基碳氢键，在光化学迷你类型均解芳烃取代中给予非典型的区域选择性。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.