Photoactivation of Stable Bonds for Chemical Conversions

在化学系化学催化项目的支持下，哈佛大学的Daniel G. Nocera教授正在研究高能量物种的产生，这些物种对于以燃料形式储存能量至关重要，并且与开发用于药物发现的新合成方法相关。光驱动低能量键与高能量键的重排是将可再生能源转化为燃料并有效利用它来驱动催化过程的核心。因此，该基金的研究重点是利用太阳能或太阳能电作为能量输入，促进分子复合物金属中心的键重排。各种现代分析技术将被应用于理解支撑感兴趣的金属配合物如何介导光和电驱动键重排的基本原理。预计这项工作的发现将为发现新的可持续化学过程提供必要的工具和知识，用于制造与社会相关的燃料和其他材料。诺塞拉教授和他的同事团队所开展的教育和推广活动，除了有望为美国的经济竞争力做出贡献的基础科学所带来的好处之外，还扩大了该奖项的广泛影响。该研究项目将哈佛大学有才华和多样化的学生引入化学前沿问题，并提供一种机制，以教育这些年轻人所需的广泛技术技能，为他们未来独立的科学事业中的关键问题做出贡献。在推广领域，Nocera教授通过他在全国新闻、电视、广播节目、电影和其他广播媒体等各种平台上的贡献，继续提高公众对化学和一般科学在解决能源和催化挑战方面所起作用的认识。Nocera实验室在扩大科学界代表性不足群体的个人参与方面取得了成功的记录，计划继续努力，通过团队的多样性建立卓越。通过光谱和合成研究的相互作用，资助的研究重点是通过激发态过渡金属配合物激活稳定键来产生高能物质的新试剂、反应和过程的创造。目前正在进行的研究有三个方面：(1)在雕刻的二级配位球内光激活金属卤化物键，目的是提高卤素自由基活化碳氢键的选择性；(2)由自由基中间体生成超还原/氧化性闭壳光试剂[这种由自由基衍生的闭壳物质可以极大地扩大光氧化还原试剂的氧化还原窗口，从而允许基于生成高活性中间体的新方法的发展]；(3)通过利用半导体光催化剂的氧化空穴（价带）和还原电子（导带），扩大了超还原性/氧化性试剂的种类。预计这项工作将产生的有影响的转变包括全氟甲基化和全氟烷基化，以及分解对环境有害的全氟羧酸的高效新工艺。在所有的光转化反应(1)-(3)中，一个有趣的可能性是引入光电化学方法来实现封闭的催化循环以及使用太阳能。光电化学方法为使用光氧化还原方法的可持续化学制造开辟了一条潜在的途径，否则它们的应用范围受到限制。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

With the support of the Chemical Catalysis Program in the Division of Chemistry, Professor Daniel G. Nocera of Harvard University is studying the generation of highly energetic species that are both critical to storing energy in the form of fuels and relevant to the development of new synthetic methods for drug discovery. The light-driven rearrangement of bonds with low energy content to ones of high energy content lies at the heart of converting renewable energy to fuels and of efficiently harnessing it to drive catalytic processes. Accordingly, the funded research focuses on facilitating bond rearrangements at the metal center of a molecular complex with solar light or solar electricity as an energy input. A variety of modern analytical techniques will be deployed to understand the fundamental principles underpinning how the metal complexes of interest mediate light- and electro-driven bond rearrangements. The findings from this work are anticipated to provide the tools and knowledge necessary for the discovery of new sustainable chemical processes for the manufacture of fuels and other materials of relevance to society. Beyond the benefits of the basic science being pursued, which are expected to contribute to the economic competitiveness of the US, the broader impacts of the award are augmented by educational and outreach activities performed by Professor Nocera and his team of coworkers. The research program introduces a talented and diverse pool of students at Harvard to forefront problems in chemistry and provides a mechanism to educate these young people with the broad technical skill set needed for them to contribute to critical problems in their future independent scientific careers. In the realm of outreach, Professor Nocera continues to raise public awareness of the role that chemistry, and science in general, can play in addressing challenges in energy and catalysis through his many contributions across a variety of platforms including national news, TV, radio programs, movies, and other broadcast media. The Nocera laboratory has a successful track record of broadening the participation of individuals belonging to groups underrepresented in science and the plan is to continue this effort to build excellence through diversity in the team.Through an interplay of spectroscopic and synthetic studies, the funded research focuses on the creation of new reagents, reactions, and processes for the generation of high energy species via the activation of stable bonds by transition metal complexes in excited states. Three lines of inquiry are being pursued: (1) photoactivation of metal-halide bonds within sculpted secondary coordination spheres with the goal of enhancing the selectivity of C-H bond activation by halogen radicals; (2) generation of super-reducing/-oxidizing closed-shell photoreagents from radical intermediates [such closed-shell species derived from radicals can greatly expand the redox window of photoredox reagents, thus allowing for the development of new methods based on the generation of highly reactive intermediates], and; (3) expansion of the types of super-reducing/-oxidizing reagents that are accessible by exploiting the oxidizing holes (in the valence band) and the reducing electrons (of the conduction band) of semiconductor photocatalysts. Among the impactful transformations that are anticipated to emerge from this work are perfluoromethylations and perfluoroalkylations, as well as efficient new processes for the decomposition of environmentally harmful perfluorocarboxylic acids. In all photoconversion reactions (1)-(3), an intriguing possibility also of interest is to introduce photoelectrochemical methods to allow a closed catalytic cycle to be achieved as well as the use of solar light. The photoelectrochemical approach opens a potential pathway to sustainable chemical manufacturing using photoredox methods which are otherwise limited in their range of applications.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.