Dinickel Active Sites Supported by Redox-Active Ligands
Dinickel Active Sites Supported by Redox-Active Ligands
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氧化还原活性配体支持的二镍活性位点
DOI：
10.1021/acs.accounts.1c00424
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发表时间：
2021
影响因子：
18.3
通讯作者：
Farley, Conner M.
中科院分区：
文献类型：
--
作者：
Uyeda, Christopher;Farley, Conner M.
发生在酶和非均相催化剂表面的氧化还原反应通常需要含有多种金属的活性位点。相比之下，具有多核活性位点的均相催化剂很少，有机金属化学领域仍然以单金属体系的研究为主导。多核催化剂由于其协同接触底物的能力而具有展示独特性能的潜力。此外，直接的金属-金属共价键可以产生新的电子构型，极大地影响底物的结合和反应性。为了有效地利用这些特征，有必要考虑在催化循环过程中避免脆弱的金属-金属键离解的策略。本报告描述了一种利用双核氧化还原活性配体实现这一目标的方法。2006年，Chirik表明吡啶二亚胺（PDI）具有足够低的π*水平，可以在低价铁配合物中氧化还原非无罪。为了扩展这一概念，我们研究了一系列萘啶-二亚胺（NDI）配体支持的二镍配合物。这些配合物可以促进广泛的双电子氧化还原过程，其中NDI配体管理电子当量，而金属保持在Ni(I) -Ni (I)状态。使用（NDI） ni2催化剂，我们发现在活性位点使用两种金属可以解决单金属系统无法充分解决的催化问题。例如，单镍配合物能够在化学计量上使芳基叠氮化物二聚形成偶氮芳烃，但由于强烈的产物抑制作用而不会翻转。相比之下，二镍配合物是该反应的有效催化剂，并通过与偶氮芳烃以高能量的顺式形式结合而避免了这种热力学汇。二镍配合物还可以通过两种金属的协同作用激活强键。降冰片二烯具有与环丙烷相似的环应变能，但不容易与单金属配合物发生C-C氧化加成。使用（NDI） ni2配合物，降冰片二烯通过乙烯基和桥头堡碳的氧化加成快速开环。对所得到的金属循环的检查表明，它是通过二次Ni−π相互作用的网络稳定的。这种反应性使催化羰基化重排的发展，形成融合的双环二烯酮。这些插图和本报告中描述的其他插图突出了金属-金属键在促进催化循环中具有挑战性的步骤或调整关键中间体的热力学景观方面的一些含义。鉴于我们的研究几乎完全集中在（NDI） ni2体系上，我们预计随着其他过渡金属组合和配体类的探索，还会发现更多这样的情况。
ConspectusRedox reactions that take place in enzymes and on the surfaces of heterogeneous catalysts often require active sites that contain multiple metals. By contrast, there are very few homogeneous catalysts with multinuclear active sites, and the field of organometallic chemistry continues to be dominated by the study of single metal systems. Multinuclear catalysts have the potential to display unique properties owing to their ability to cooperatively engage substrates. Furthermore, direct metal-to-metal covalent bonding can give rise to new electronic configurations that dramatically impact substrate binding and reactivity. In order to effectively capitalize on these features, it is necessary to consider strategies to avoid the dissociation of fragile metal–metal bonds in the course of a catalytic cycle. This Account describes one approach to accomplishing this goal using binucleating redox-active ligands.In 2006, Chirik showed that pyridine–diimines (PDI) have sufficiently low-lying π* levels that they can be redox-noninnocent in low-valent iron complexes. Extending this concept, we investigated a series of dinickel complexes supported by naphthyridine–diimine (NDI) ligands. These complexes can promote a broad range of two-electron redox processes in which the NDI ligand manages electron equivalents while the metals remain in a Ni(I)–Ni(I) state.Using (NDI)Ni2catalysts, we have uncovered cases where having two metals in the active site addresses a problem in catalysis that had not been adequately solved using single-metal systems. For example, mononickel complexes are capable of stoichiometrically dimerizing aryl azides to form azoarenes but do not turn over due to strong product inhibition. By contrast, dinickel complexes are effective catalysts for this reaction and avoid this thermodynamic sink by binding to azoarenes in their higher-energy cis form.Dinickel complexes can also activate strong bonds through the cooperative action of both metals. Norbornadiene has a ring-strain energy that is similar to that of cyclopropane but is not prone to undergoing C–C oxidative addition with monometallic complexes. Using an (NDI)Ni2complex, norbornadiene undergoes rapid ring opening by the oxidative addition of the vinyl and bridgehead carbons. An inspection of the resulting metallacycle reveals that it is stabilized through a network of secondary Ni−π interactions. This reactivity enabled the development of a catalytic carbonylative rearrangement to form fused bicyclic dienones.These vignettes and others described in this Account highlight some of the implications of metal–metal bonding in promoting a challenging step in a catalytic cycle or adjusting the thermodynamic landscape of key intermediates. Given that our studies have focused nearly exclusively on the (NDI)Ni2system, we anticipate that many more such cases are left to be discovered as other transition-metal combinations and ligand classes are explored.