Recently developed covalent functionalization chemistry for MoS₂ in the 1T′ phase enables the formation of covalent chalcogenide–carbon bonds from alkyl halides and aryl diazonium salts. However, the coverage of functional groups using this method has been limited by the amount of negative charge stored in the exfoliated MoS₂ sheets to <25–30% per MoS₂ unit. We report, herein, a reductant-activated functionalization, wherein one-electron metallocene reductants, such as nickelocene, octamethylnickelocene, and cobaltocene, are introduced during functionalization with methyl and propyl halides to tune the coverage of the alkyl groups. The reductant-activated functionalization yields functional group coverages up to 70%, ∼1.5–2 times higher than the previous limit, and enables functionalization by weak electrophiles, such as 1-chloropropane, that are otherwise unreactive with chemically exfoliated MoS₂. We also explored the dependence of coverage on the strength of the leaving group and the steric hindrance of the alkyl halide in the absence of reductants and showed that functionalization was ineffective for chloride leaving groups and for secondary and tertiary alkyl iodides. These results demonstrate a substantial increase in coverage compared to functionalization without reductants, and may impact the performance of these materials in applications reliant on surface interactions. Furthermore, this method may be applicable to the covalent functionalization of similar layered materials and metal chalcogenides.

中文翻译：

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1T'-MoS _2的还原剂活化，高覆盖率，共价官能化

最近开发的1T'相中MoS _2的共价官能化化学反应可从烷基卤化物和芳基重氮盐形成共价硫族化物-碳键。但是，使用此方法对官能团的覆盖范围受到剥落的MoS ₂薄片中存储的负电荷量的限制，即每个MoS ₂的负电荷量<25–30％单元。我们在本文中报道了还原剂活化的官能化，其中在用甲基和丙基卤化物官能化的过程中引入单电子茂金属还原剂，例如镍茂，八甲基镍茂和钴茂，以调节烷基的覆盖范围。还原剂激活的官能化可产生高达70％的官能团覆盖率，是上一个上限的约1.5至2倍，并能够通过弱亲电试剂（例如1-氯丙烷）进行官能化，否则这些亲电试剂不会与化学脱落的MoS _2发生反应。我们还探讨了在不存在还原剂的情况下，覆盖范围对离去基团强度和烷基卤化物空间位阻的依赖性，并表明官能化对于氯化物离去基团以及仲和叔烷基碘均无效。这些结果表明，与没有还原剂的功能化相比，覆盖率有了实质性的提高，并且可能在依赖于表面相互作用的应用中影响这些材料的性能。此外，该方法可适用于相似的层状材料和金属硫属元素化物的共价官能化。