Claisen rearrangement of graphite oxide: a route to covalently functionalized graphenes.

The MIT Faculty has made this article openly available. Please share how this access benefits you. Your story matters. The chemical modification of nano-or micro-molecular surfaces is widely used for the precise structural and/or electrical manipulation of bulk materials. [1] In particular, atomically thin graphitic molecules such as fullerene, carbon nanotubes, and graphene display pronounced physicochemical and electronic changes after synthetic derivatization of their surfaces. [2] In many cases these graphitic substrates can be imbued with a wide range of desirable attributes such as increased solubility in a specific solvent, enhanced mechanical properties, chemosensing, and conductance changes. Because of these attributes, numerous prepared graphitic derivatives have been utilized in a variety of academic and industrial applications. Unfortunately, few synthetic methods currently exist to covalently functionalize the surface of graphene. [4] This deficiency is due to both the use of meta-stable colloidal suspensions of reduced graphite oxide (GO) as the starting material for many transformations, [5] as well as the decreased chemical reactivity of graphene in comparison to the more strained fullerene or carbon nanotubes. [6],[7] Herein we report the covalent functionalization of soluble, exfoliated graphite oxide through a Claisen rearrangement (Scheme 1). Specifically, the allylic alcohol functional groups found on the surface of GO, [8] are converted in-situ to vinyl allyl ethers, and allylically transposed in a sigmatropic-type fashion to form new carbon-carbon bonds. As a direct result of this transformation robust carbonyls are installed on the surface, which can undergo subsequent synthetic manipulations. The Eschenmoser-Claisen rearrangement variant was chosen as the proof of principle test reaction on GO (Scheme 1, where R = N(CH 3) 2). In this reaction allylic alcohols are converted to γ,δ-unsaturated N,N-dimethylamides through the use of the vinyl transfer reagent N,N-dimethylacetamide dimethyl acetal (DMDA). This reaction was chosen specifically for the following reasons: 1) the ability to quantitatively evaluate the efficacy of the transformation through nitrogen incorporation, 2) DMDA's chemospecificity for alcohol functional groups, 3) only thermal treatment of DMDA is necessary to affect the vinyl group transfer, and 4) the formation of quaternary carbon-carbon bonds is well established using the Eschenmoser-Claisen variant. Scheme 1. Allylic oxygen to carbon bond transposition on graphite oxide (additional substrate oxygenation removed for clarity). For the Eschenmoser-Claisen rearrangement variant R = N(CH 3) 2. We began the investigations into the proposed transformation by mixing graphite oxide with DMDA (~2 equivalents per oxygen on GO, see Supporting Information) [10] in …