High-Yield Alkylation and Arylation of Graphene via Grignard Reaction with Fluorographene

C functionalization of graphene significantly broadens its application potential via tuning its electronic and surface properties. Therefore, a wide range of dry and wet chemistry approaches have been developed for graphene functionalization. Despite recent progress in this field, covalent modification of graphene is still hampered by its low reactivity. Moreover, the reactivity depends on the type of graphene support and number of graphene layers. Consequently, there is a need for new strategies that permit high yielding graphene functionalization under more controlled conditions. Very recently, fluorographene (FG), a stoichiometric (C1F1) and well-established graphene derivative, has been shown to be susceptible to reductive defluorination and nucleophilic attack. These findings suggest that FG may be a useful alternative material to graphene for the preparation of graphene derivatives. This idea is supported by recent achievements in the field employing nucleophilic substitution of fluorine atoms by other groups, such as sulfhydryl, amino, alkoxy, dichlorocarbene and urea. However, efficient reaction of FG with Grignard reagents to allow high yield alkylation and arylation of graphene has not yet been reported. The Grignard reaction is one of the most well-established methodologies for the formation of C−C bonds in organic chemistry. Grignard reagents bear a nucleophilic carbon atom owing to its bonding to magnesium, and the in situ formed hydrocarbon anion can attack electrophilic carbons, such as the carbons of FG. The Grignard reaction has been successfully applied to fluorinated carbon nanotubes, but to date, there is only one report regarding the covalent modification of chlorinated graphene with Grignard reagents. Very recently, the same group reported that Grignard reaction on fluorinated epitaxial graphene was not feasible. In the present work, we report the first successful covalent modification of FG based on the Grignard reaction, which yielded homogeneous and high-density (5.5−11.2%) functionalization of the graphene surface. Three different types of organometallic reagents, containing alkane (pentyl), alkene (allyl), and aryl (anisolyl or p-methoxyphenyl) moieties, reacted successfully, unlike the reaction with the ethynyl reagent. This behavior was rationalized in terms of the nucleophilicities of the reactive centers, assessed by computational chemistry (Figure 1). The new covalently functionalized graphene derivatives were characterized by complementary techniques: spectroscopic, thermogravimetric and microscopic. In addition, we used density functional theory (DFT) calculations to evaluate the thermodynamic stabilities of the chemically modified graphenes, and delineate the influence of the different covalently attached groups on the electronic properties of graphene. Initially, a FG suspension was prepared by sonication of graphite fluoride (GF) in dry tetrahydrofuran. Next, the Grignard reagent (Figure 1) was added dropwise to the suspension and the mixture was stirred under nitrogen for 5 h. Afterward, excess Grignard reagent was quenched with a saturated aqueous solution of ammonium chloride and the material was washed with a copious amount of water. To remove any residues of magnesium salts, the product was resuspended in aqueous 5% HCl solution and washed with water, ethanol and dichloromethane, consecutively. When ethynylmagnesium bromide was used as a precursor compound for the generation of the nucleophile (ethynyl group), the reaction with FG was unsuccessful, even after