Redox-active ligands and their coordination complexes

基于过渡金属的化合物在令人难以置信的广泛应用中使用。它们被用作试剂和催化剂来制造新药、聚合物和其他重要的化学品。它们还具有物理性质(光吸收、发射、磁性…)。在从核磁共振到电池再到替代能源的许多高科技应用中都得到了利用。无论具体应用如何，化学家通常都会通过仔细选择与金属结合的配体(或设计新的配体)来定制金属络合物的性质。“配体设计”的想法是过渡金属化学的许多方面所特有的。 总的来说，这些努力都是基于这样一个前提，即金属络合物的性质主要来源于金属，而配体在微调这些性质方面起着支撑作用。另一种方法包括使用配体，这些配体本身具有一些活性功能。在我的研究项目中感兴趣的配体性质是氧化还原活性。顾名思义，氧化还原活性配体(RAL)可以像许多过渡金属一样被氧化或还原。这类配体已经知道了大约50年，但直到最近，人们的主要注意力都集中在简单地试图了解缩醛配合物的电子结构上。 在过去的十年里，人们越来越认识到乙醛配合物可能具有非常有用的应用：一些重要的技术物理性质(光学、磁性、分子开关)源于基于配体的氧化还原活性。而利用配体为中心的氧化还原活性来制造新的/更有效/更便宜的试剂和催化剂的可能性正开始受到全世界的关注。这些基本想法仍处于探索的早期阶段；还需要更多的工作来确定Ral复合体的潜在用途。 这一建议概述了基于新型氧化还原活性配体的缩醛配合物的合成、性质和用途的研究。该领域的其他研究人员正专注于成熟的RAL类型；我的目标是尝试通过开发我实验室中正在开发的非传统系统来扩展“RAL工具包”。我们发现了两种全新的氧化还原活性配体，一种是基于一类稳定的自由基，另一种是基于一种工业上重要的有机染料。这两种化合物都很容易制备，并且都具有不寻常/独特的性质，可以通过传统的取代基效应进行调节。拟议的研究主要是以发现为导向的，因为我们将检查我们的AL络合物的一系列性质。这项工作涉及到大量的化学合成(设计和制造目标分子，基于它们可能做的事情的假设)。在某些情况下，“性质”是反应性/催化，而在另一些情况下，重点是电学/光学性质。我们将评估我们的系统相对于其他RAL络合物(以及更广泛地说，不基于RAL的其他金属络合物)的优势和劣势，并希望通过这样做：(I)有助于集体理解氧化还原活性配体的基本性质；(Ii)确定催化和/或先进材料方面的新发展机会。

Compounds based on the transition metals are used in an incredibly broad spectrum of applications. They are used as reagents and as catalysts to make new drugs, polymers, and other important classes of chemicals. They also possess physical properties (light absorption, emission, magnetism…) that are exploited in many high-tech applications ranging from MRI to batteries to alternative energy. Whatever the particular application, chemists typically work to tailor the properties of metal complexes by carefully selecting the ligands (or designing new ones) that are bound to the metal. The idea of “ligand design” is endemic to many, many aspects of transition metal chemistry. By and large these efforts are based on the premise that the properties of metal complexes stem principally from the metal, and the ligands play a supporting role in fine tuning these properties. An alternative approach involves using ligand which themselves have some active function. The ligand property of interest in my research program is redox activity. As their name suggests, "redox-active ligands" (RALs) can be oxidized or reduced analogously to many transition metals. These sorts of ligands have been known for about 50 years but until recently the main focus was on simply trying to understand the electronic structure of RAL complexes. In the past decade there has been growing recognition that RAL complexes could possess very useful applications: Several technologically important physical properties (optical, magnetic, molecular switching) stem from ligand-based redox activity. And the possibility of harnessing ligand-centered redox activity to make new/more effective/cheaper reagents and catalysts is beginning to receive worldwide attention. These general ideas are still in early stages of exploration; more work is needed to determine the potential uses of RAL complexes. This proposal outlines research into the synthesis, properties and uses of RAL complexes based on new kinds of redox-active ligands. Other researchers in this field are focusing on well-established types of RALs; my goals are to try to broaden the “RAL toolkit” by developing non-traditional systems under development in my lab. We have discovered two fundamentally new types of redox-active ligand, one based on a class of stable radical and the other based on an industrially important organic dye. Both are straightforward to make, and both have unusual/distinctive properties which can be modulated through conventional substituent effects. The proposed research is principally discovery-oriented, in that we will examine a range of properties for our RAL complexes. This work involves a lot of chemical synthesis (designing and making target molecules, based on hypotheses of what they might "do"). In some cases the “property” is reactivity/catalysis, whereas in others the focus is on electro/optical properties. We will assess the strengths and weaknesses of our systems in relation to other RAL complexes (and more generally, other metal complexes not based on RALs) and in so doing we hope to (i) contribute to the collective understanding of the fundamental nature of redox-active ligands and (ii) identify new opportunities for development in catalysis and/or advanced materials.