Reductant-Activated, High-Coverage, Covalent Functionalization of 1T′-MoS₂

Abstract

Recently developed covalent functionalization chemistry for MoS2 in the 1Tʹ 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 negative charge stored in the exfoliated MoS2 sheets to <25-30% per MoS2 unit. We report herein a reductantactivated 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.

Covalent Functionalization of Nickel Phosphide Nanocrystals with Aryl-Diazonium Salts

“…This concept was recently validated by the Lewis group who showed that the functionalization density of MoS2 by alkyl iodide species could be increased by adding sacrificial reductants to the reaction mixture. 113 This study demonstrated a strong correlation between the strength of the reductant and the coverage of functional groups, supporting our hypothesis that each surface functional group equivalent becomes increasingly difficult to generate and is strongly dependent on the thermodynamic driving force for both generating the radical species and facilitating surface-C bond formation.…”

Covalent Functionalization of Nickel Phosphide Nanocrystals with Aryl-Diazonium Salts

“…This concept was recently validated by the Lewis group who showed that the functionalization density of MoS2 by alkyl iodide species could be increased by adding sacrificial reductants to the reaction mixture. 112 This study demonstrated a strong correlation between the strength of the reductant and the coverage of functional groups, supporting our hypothesis that each surface functional group equivalent becomes increasingly difficult to generate and is strongly dependent on the thermodynamic driving force for both generating the radical species and facilitating surface-C bond formation.…”

Covalent functionalization of molybdenum disulfide by chemically activated diazonium salts

“…Interestingly, a similar approach, where alkyl halides were chemically reduced, has recently been used to functionalize 1T'-MoS2. 26 It has been shown earlier that, in the case of diazonium salts, chemical activation via ascorbic acid or iron powder can form aryl radicals for covalent functionalization of a wide range of substrates. [27][28][29] Even before that, this approach was used to perform aryl-aryl coupling in solution, for instance using iodide to induce the reduction of aryl diazonium salts, obtaining quantitative yield of biaryls.…”