Photoactivation of Stable Bonds for Chemical Conversions

在化学系化学催化计划的支持下，哈佛大学的丹尼尔·G·诺塞拉教授正在研究高能物种的产生，这些物种对以燃料的形式储存能量至关重要，也与开发新的合成方法用于药物发现有关。光驱动的低能量含量的键到高能量含量的键的重排是将可再生能源转换为燃料并有效利用它来驱动催化过程的核心。因此，受资助的研究重点是促进分子络合物金属中心的键重排，以太阳能或太阳能电力作为能量输入。将采用各种现代分析技术来理解支持感兴趣的金属络合物如何调解光驱动和电子驱动的键重排的基本原理。这项工作的结论预计将提供必要的工具和知识，为发现制造燃料和其他与社会有关的材料的新的可持续化学工艺提供必要的工具和知识。诺切拉教授和他的同事们开展的教育和外展活动，除了将有助于提高美国经济竞争力的基础科学所带来的好处外，诺塞拉教授和他的同事们开展的教育和推广活动也扩大了该奖项的广泛影响。该研究项目向哈佛大学引进了一批才华横溢的多样化学生，让他们了解化学领域的前沿问题，并提供了一种机制，为这些年轻人提供广泛的技术技能，使他们能够在未来独立的科学职业生涯中为关键问题做出贡献。在推广领域，诺切拉教授通过他在国家新闻、电视、广播节目、电影和其他广播媒体等各种平台上的许多贡献，继续提高公众对化学和一般科学在应对能源和催化方面的挑战方面所发挥的作用的认识。诺切拉实验室在扩大属于科学中代表性不足的基团的个人参与方面有着成功的记录，计划继续这一努力，通过团队中的多样性建立卓越。通过光谱和合成研究的相互作用，受资助的研究专注于创造新的试剂、反应和过程，通过激发态的过渡金属络合物激活稳定键来产生高能物种。目前正在进行三个方面的研究：(1)雕刻二次配位球内金属-卤化物键的光活化，目的是提高卤素自由基激活C-H键的选择性；(2)从自由基中间体[这种源于自由基的闭壳物种可以极大地扩大光氧化还原试剂的氧化还原窗口，从而允许开发基于产生高活性中间体的新方法]；(3)利用半导体光催化剂的氧化空穴(价带)和还原电子(导带)可获得的超还原/氧化试剂种类的扩展。这项工作预计会产生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有效新工艺。在所有的光转化反应(1)-(3)中，一个有趣的可能性也是引入光电化学方法，以实现闭合催化循环以及利用太阳光。光电化学方法开辟了一条使用光氧化还原方法进行可持续化学制造的潜在途径，否则其应用范围将受到限制。该奖项反映了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。

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.