Successive Free-Radical C(sp ² )–C(sp ² ) Coupling Reactions to Form Graphene

Abstract

Graphene has aroused great interest on account of its exciting properties and potential applications, but its production on a large-scale still presents considerable challenges. Here, we report the synthesis of predominately few-layer graphene, due to - stacking, as well as single-layer graphene, from reaction between hexabromobenzene and sodium metal, followed by annealing treatment to improve crystallinity.The reaction proceeds via a free-radical C(sp 2 )-C(sp 2 ) coupling mechanism, which is supported by theoretical calculations. The graphene can host unpaired spins, leading to a short acquisition time for a solid-state nuclear magnetic resonance 13 C spectrum from unlabeled graphene, which is ascribed to the very short spinlattice relaxation time. High catalytic activity for transforming amine to imine with a conversion of >99% and a yield of 97% is demonstrated, and high electronic conductivity of 10 5 Sm -1 has been found by terahertz spectroscopy. The reaction represents a method for synthesizing graphene with a high spin concentration from perbrominated benzene molecules by using an active metallic agent, such as, Na or Li, or Mg.

Electron Spin Catalysis with Graphene Belts

“…Some short‐range ordering of the GBs is demonstrated by both X‐ray diffraction (Figure S3) and Raman spectroscopy (Figure 1f) and is consistent with what is typically seen in defective graphene. Following normalization processing, [5] the X‐ray photoelectron spectroscopy (XPS) data (Figure 1g) identified that the oxygen content of the GBs was 5.89 at.% (Figure 1g, Figure S4, and Tables S3 & S4). The fraction of sp 2 carbon relative to the total carbon was 82.8 at.%.…”

“…The fitting results of the C1s signal showed that the concentration of C−H bonds was 16.5 at.%, which is consistent with the proton hyperfine coupling effects observed in the ESR data (see below). In the 13 C solid‐state nuclear magnetic resonance (ssNMR) spectrum (Figure 1h), the peaks at 128.03 ppm, and 140.75 ppm, identified by the cross‐polarization‐polarization inversion (CPPI) technique, belong to the hydrogen‐bonded aromatic carbons and carbon‐attached aromatic carbons, respectively (Figure S5), [13] while the 1 H ssNMR characterization showed that two types of protons were found in the product (Figure 1i and Figure S6); these correspond to aromatic hydrogens ( δ =6.86 ppm), and those from shielded hydroxyl hydrogens ( δ =1.57 ppm), respectively [5] …”

“…This is slightly larger than the free‐electron value for g e of 2.00232, which we attribute to oxygen content at the surface of the product due to the radical reacting with O 2 and/or CO 2 in the termination step of the coupling reaction (Figure 1j). [5] GB samples were annealed at different temperatures from 700 °C to 1000 °C for 2 h in air (denoted as GB‐T, where T represents temperature) (Figures S8–S16 and Table S5–S10). In addition to samples GB‐700, GB‐800, GB‐900, and GB‐1000, a further sample, which was annealed at 900 °C for 2 h in an H 2 /Ar mixed gas, is denoted as GB‐900‐H 2 /Ar.…”

“…However, natural sources of many metals are limited [4] and more attention is now being paid to the development of metal‐free alternatives. Carbon, which is both abundant and widely available, is a promising candidate as an alternative to traditional catalysts, [5, 6] and several carbons and doped carbon materials have been reported as catalysts. Important examples include their use in aerobic oxidation reactions, [7–9] such as imine synthesis via the dehydrogenation of an amine by using O 2 as the hydrogen acceptor [5, 7] .…”

“…Carbon, which is both abundant and widely available, is a promising candidate as an alternative to traditional catalysts, [5, 6] and several carbons and doped carbon materials have been reported as catalysts. Important examples include their use in aerobic oxidation reactions, [7–9] such as imine synthesis via the dehydrogenation of an amine by using O 2 as the hydrogen acceptor [5, 7] . They have also been used for transformations beyond organic syntheses, such as in the oxygen reduction reaction (ORR), [9] which is one of the most challenging chemical processes at present.…”