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

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%, similar to 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.