Martínez-Vivas Sebastián, Poyatos Macarena, Peris Eduardo
Institute of Advanced Materials (INAM), Centro de Innovación en Química Avanzada (ORFEO-CINQA), Universitat Jaume I Av. Vicente Sos Baynat s/n Castellón E-12071 Spain
Chem Sci. 2025 Mar 7;16(15):6257-6264. doi: 10.1039/d4sc08203f. eCollection 2025 Apr 9.
We report the preparation of two Pd(ii) complexes based on (CCC)-pincer-NHC (NHC = N-heterocyclic carbene) ligands. One of these complexes features an NDI unit (NDI = naphthalene-diimide) attached to the CCC-pincer ligand. Reacting these complexes with bromine results in the formation of the corresponding palladium(iv) complexes [PdBr(NDI-CCC)] and [PdBr(CCC)]. The NDI-containing pincer complex exhibits a strong sensitivity to fluoride ions, which can induce a one-electron reduction of the naphthalene-diimide moiety. We demonstrate that the addition of fluoride induces the reduction of the NDI moiety the formation of hydroxide anions, which are the effective reducing agents of the process. The addition of fluoride significantly affects the reactivity of the NDI-containing palladium complexes. For example, the palladium(iv) complex [PdBr(NDI-CCC)] can transfer bromide to styrene in a stoichiometric manner, but this reaction is inhibited in the presence of fluoride. Similarly, the palladium(ii) complex [PdI(NDI-CCC)] catalyzes the oxidative homocoupling of arylpyridines, but its catalytic activity is quenched when excess fluoride is added. Notably, we demonstrate that this process can be deactivated and reactivated by sequentially introducing an excess of fluoride and NOBF, revealing a rare instance of a redox-switchable process within a Pd(ii)/Pd(iv) catalytic cycle. In contrast, the (CCC)-pincer palladium(ii) and (iv) complexes lacking the NDI unit show no sensitivity to fluoride. Our study demonstrates that a simple reagent, such as the fluoride anion, can effectively modulate the reactivity of the Pd(ii)/Pd(iv) pair. More broadly, it shows that fluoride serves as a simpler alternative to the metal-based reducing agents commonly used in redox-switchable catalysis.
我们报道了基于（CCC）-钳形-NHC（NHC = N-杂环卡宾）配体的两种钯（II）配合物的制备。其中一种配合物的特点是在CCC-钳形配体上连接了一个NDI单元（NDI = 萘二酰亚胺）。这些配合物与溴反应会生成相应的钯（IV）配合物[PdBr（NDI-CCC）]和[PdBr（CCC）]。含NDI的钳形配合物对氟离子表现出很强的敏感性，氟离子可诱导萘二酰亚胺部分发生单电子还原。我们证明，氟离子的加入会诱导NDI部分的还原以及氢氧根阴离子的形成，而氢氧根阴离子是该过程的有效还原剂。氟离子的加入显著影响含NDI的钯配合物的反应活性。例如，钯（IV）配合物[PdBr（NDI-CCC）]能以化学计量的方式将溴转移到苯乙烯上，但在氟离子存在下该反应受到抑制。同样，钯（II）配合物[PdI（NDI-CCC）]催化芳基吡啶的氧化均偶联反应，但加入过量氟离子时其催化活性会被淬灭。值得注意的是，我们证明通过依次加入过量的氟离子和NOBF₄，这个过程可以被停用和重新激活，揭示了在钯（II）/钯（IV）催化循环中一个罕见的氧化还原可切换过程的实例。相比之下，不含NDI单元的（CCC）-钳形钯（II）和钯（IV）配合物对氟离子不敏感。我们的研究表明一种简单的试剂，如氟离子阴离子，可以有效地调节钯（II）/钯（IV）对的反应活性。更广泛地说，它表明氟离子是氧化还原可切换催化中常用的金属基还原剂的一种更简单的替代品。
