Redox-Active Carboranyl-Based Lewis Acids for Targeted N-H Bond Weakening

在化学部化学合成项目的支持下，加州大学圣巴巴拉分校化学系的Gabriel Menard将研究一类被称为碳硼烷的化合物激活氨中N-H键的能力。该项目的动机是需要开发储能技术，以促进可再生能源（RE）生产和分配的持续增长。对于可再生能源的实际应用，高效的能量存储至关重要。这是因为，例如，在阳光灿烂的时期获得了多余的能量，必须储存起来，以便在太阳不灿烂的时候提供能量。一种新兴的储存技术涉及使用氨。氨是世界上产量第二大的化学物质，它是一种低成本、高能量密度的分子，氢含量高，并在全球拥有成熟的分销基础设施。然而，它在可再生能源储存中的应用依赖于它对氢（一种清洁燃料）和氮的有效转化。该项目将开发一套称为碳硼烷的分子，能够利用电能将氨转化为氢和氮。这项工作的重点是最大限度地提高碳硼烷削弱氨中的化学键的能力，这促进了转化为氢和氮的基本步骤。该项目将导致培训高技能的化学家，包括妇女和代表性不足的少数民族科学家。此外，梅纳德博士每月举办“科学酒吧之夜”活动，来自校园的科学家以开放和可访问的方式向公众展示他们的研究。本研究旨在开发碳硼烷反应活性，以启动氨中强N-H键的激活，以释放氢（或其等价物）。转化NH3（氨）的潜在挑战在于充分激活强N-H键以促进随后的N-N键形成。目前正在开发一种总体策略，通过合成近端、氧化还原活性、碳硼烷（Cb）附加的刘易斯酸中心来系统地控制N-H键解离自由能，这种中心允许通过调整Cb笼电子和这些化合物的刘易斯酸性质来解耦和控制热化学参数。这将允许系统控制和削弱配位NH3的N-H键，并将其部分分裂为肼和氢当量。具体目标包括：1)合成含cb的近端Lewis酸性体系；2)通过热化学和结构调控调控H2的自发释放；3)使用电化学反应器关闭循环。该项目涉及一项重要的努力，以招收和留住多样化的学生群体，并有一个面向非传统科学教育受众的外联部分。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 Synthesis Program of the Chemistry Division, Gabriel Menard of the Department of Chemistry at University of California – Santa Barbara will investigate the ability of a class of compounds, called carboranes, to activate N-H bonds in ammonia. This project is motivated by the need to develop energy storage technologies to facilitate the sustained growth of renewable energy (RE) production and distribution. For the practical use of RE, efficient energy storage is vital. This is because excess energy is obtained, for example, during periods when the sun is shining and must be stored in order to provide energy when the sun is not shining. An emerging storage technique involves use of ammonia. Ammonia, the second most produced chemical in the world, is a low-cost, energy-dense molecule with a high hydrogen content and an established global distribution infrastructure. However, its use in RE storage relies on its efficient conversion to hydrogen – a clean fuel – and nitrogen. This project will develop a set of molecules, called carboranes, that are capable of utilizing electrical energy to transform ammonia into hydrogen and nitrogen. The work focuses on the maximizing the ability of the carboranes to weaken the chemical bonds in ammonia, which prompts the fundamental steps involved in the conversion to hydrogen and nitrogen. The project will lead to the training of highly skilled chemists, including women and underrepresented minority scientists. In addition, Dr. Menard hosts monthly “Science Pub Night” event, where scientists from campus present their research to the public in an open and accessible way. This research aims to develop carborane reactivity for initiating the activation of the strong N–H bonds in ammonia for hydrogen release (or its equivalents). The underlying challenge in converting NH3 (ammonia) lies in activating the strong N–H bonds sufficiently to prompt subsequent N–N bond formation. A general strategy is being developed to systematically control N–H bond dissociation free energy by synthesizing proximal, redox-active, carborane (Cb)-appended Lewis acidic centers that allow for the decoupling and control of the thermochemical parameters by tuning the Cb cage electronics and Lewis acidic properties of these compounds. This will allow the systematic control and weakening of the N–H bonds of coordinated NH3 and target its partial splitting to hydrazine and hydrogen equivalents. The Specific Aims include: 1) the synthesis of Cb-appended, proximal Lewis acidic systems; 2) targeting the spontaneous release of H2 through thermochemical and structural control, and; 3) closing the cycle using an electrochemical reactor. The project involves a significant effort to recruit and retain a diverse group of students and an outreach component target non-traditional audiences for science education.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.