Bimetallic motifs are a structural feature common to some of the most effective and synthetically useful catalysts known, including in the active sites of many metalloenzymes and on the surfaces of industrially relevant heterogeneous materials. However, the complexity of these systems often hampers detailed studies of their fundamental properties. To glean valuable mechanistic insight into how these catalysts function, this research group has prepared a family of dinucleating 1,8-naphthyridine ligands that bind two first-row transition metals in close proximity, originally designed to help mimic the proposed active site of metal oxide surfaces. Of the various bimetallic combinations examined, dicopper(I) is particularly versatile, as neutral bridging ligands adopt a variety of different binding modes depending on the configuration of frontier orbitals available to interact with the Cu centers. Organodicopper complexes are readily accessible, either through the traditional route of salt metathesis or via the activation of tetraarylborate anions through aryl group abstraction by a dicopper(I) unit. The resulting bridging aryl complexes engage in C–H bond activations, notably with terminal alkynes to afford bridging alkynyl species. The μ-hydrocarbyl complexes are surprisingly tolerant of water and elevated temperatures. This stability was leveraged to isolate a species that typically represents a fleeting intermediate in Cu-catalyzed azide–alkyne coupling (CuAAC); reaction of a bridging alkynyl complex with an organic azide afforded the first example of a well-defined, symmetrically bridged dicopper triazolide. This complex was shown to be an intermediate during CuAAC, providing support for a proposed bimetallic mechanism. These platforms are not limited to formally low oxidation states; chemical oxidation of the hydrocarbyl complexes cleanly results in formation of mixed valence Cu^ICu^II complexes with varying degrees of distortion in both the bridging moiety and the dicopper core. Higher oxidation states, e.g., dicopper(II), are easily accessed via oxidation of a dicopper(I) compound with air to give a Cu^II₂(μ-OH)₂ complex. Reduction of this compound with silanes resulted in the unexpected formation of pentametallic copper(I) dihydride clusters or trimetallic monohydride complexes, depending on the nature of the silane. Finally, development of an unsymmetrical naphthyridine ligand with mixed donor side-arms enables selective synthesis of an isostructural series of six heterobimetallic complexes, demonstrating the power of ligand design in the preparation of heterometallic assemblies.

中文翻译：

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果壳中的双金属化合物：螯合萘啶基配体支持的络合物。

双金属基序是一些已知的最有效和合成上有用的催化剂共有的结构特征，包括在许多金属酶的活性部位和工业上相关的异质材料的表面上。但是，这些系统的复杂性通常会妨碍对其基本属性的详细研究。为了收集有关这些催化剂如何发挥作用的有价值的机理见解，该研究小组准备了一系列成核的1,8-萘啶配体家族，它们紧密地结合两个第一行过渡金属，最初旨在帮助模拟拟议的金属氧化物活性位点表面。在所研究的各种双金属组合中，双铜（I）特别通用，由于中性桥联配体根据可与铜中心相互作用的前沿轨道的构型，采用各种不同的结合方式。有机二铜配合物很容易获得，既可以通过传统的盐复分解途径，也可以通过双铜（I）单元通过芳基的提取来激活四芳基硼酸根阴离子。生成的桥联芳基络合物参与C–H键的活化，特别是与末端炔烃结合以提供桥联炔基。μ-烃基络合物出人意料地耐受水和高温。利用这种稳定性来分离通常代表在铜催化的叠氮化物-炔烃偶联（CuAAC）中短暂的中间体的物种。炔基络合物与有机叠氮化物的反应得到了定义明确的第一个例子，对称桥联的双铜三唑化物。该配合物被证明是CuAAC的中间体，为拟议的双金属机理提供了支持。这些平台不限于形式上低的氧化态。烃基配合物的化学氧化干净地导致形成混合价铜^I Cu ^II复合物在桥连部分和双铜芯中都具有不同程度的变形。较高的氧化态（例如dicopper（II））可通过将dicopper（I）化合物与空气氧化而轻松获得Cu ^II ₂（μ-OH）₂络合物。用硅烷还原该化合物导致意外地形成五金属铜（I）二氢化物簇或三金属一氢化物络合物，具体取决于硅烷的性质。最后，开发具有混合供体侧臂的不对称萘啶配体使得能够选择性合成六个异双金属配合物的同构系列，从而证明了配体设计在制备异金属组件中的能力。