An efficient solvent-free synthetic method for the preparation of diphosphonium substituted naphthalenediimide (NDI) radical ions [NDI(PR₃)₂]˙⁺ Br⁻ (R = alkyl/aryl) with excellent yields and ambient stability has been described. A diverse range of trialkyl- and triarylphosphines along with different groups at the axial-positions of the NDI were assessed to verify the efficacy of this new synthetic protocol. A library comprising 24 ambient stable radical ions was synthesized and isolated via solvent-free and conventional heating conditions. The reactions were found to be quite fast and could be completed within 10–20 minutes. In addition, we applied sonication to synthesize the NDI radical ions, when the phosphine reactants exist in the liquid state. Intriguingly, NDI radical ion formation was also observed even on manual grinding of the reactants in a mortar and pestle, although with poor yields. Furthermore, we also realized NDI radical ions in moderate yields by applying ball mill grinding. In addition, we have made an attempt to unearth the most plausible reaction mechanism for these reactions. Importantly, this is the first instance whereby synthetic radical ion chemistry has been brought under the realm of green synthesis. The other significant aspect of our findings is the eco-friendly formation of two consecutive C–P bonds and the in situ one-electron transfer, which can have vital ramifications in organophosphorus and electron transfer chemistry.

中文翻译：

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环境稳定的萘二酰亚胺自由基离子：通过无溶剂，超声处理，机械研磨或研磨方案进行合成

对于二鏻取代的萘二酰亚胺（NDI）基团的离子的制备一种有效的无溶剂合成法[NDI（PR ₃）₂ ]˙ ⁺溴^-（R =烷基/芳基）具有优良的产率和环境稳定性进行了说明。评估了各种各样的三烷基和三芳基膦以及NDI轴向位置的不同基团，以验证该新合成方案的功效。合成了一个包含24个环境稳定的自由基离子的文库，并通过无溶剂和常规加热条件。发现反应非常快，可以在10至20分钟内完成。此外，当膦反应物以液态存在时，我们应用超声处理来合成NDI自由基离子。有趣的是，即使在研钵和研杵中手动研磨反应物，也观察到NDI自由基离子的形成，尽管收率很低。此外，通过球磨机研磨，我们还以中等收率实现了NDI自由基离子。此外，我们已尝试发掘这些反应最合理的反应机理。重要的是，这是将合成自由基离子化学引入绿色合成领域的第一个实例。原位单电子转移，在有机磷和电子转移化学中可能产生重要的影响。