Ullmann-Like Covalent Bond Coupling without Participation of Metal Atoms

Abstract

Ullmann-like on-surface synthesis is one of the most appropriate approaches for the bottom-up fabrication of covalent organic nanostructures and many successes have been achieved. The Ullmann reaction requires the oxidative addition of a catalyst (a metal atom in most cases): the metal atom will insert into a carbon–halogen bond, forming organometallic intermediates, which are then reductively eliminated and form C–C covalent bonds. As a result, traditional Ullmann coupling involves reactions of multiple steps, making it difficult to control the final product. Moreover, forming the organometallic intermediates will potentially poison the metal surface catalytic reactivity. In the study, we used the 2D hBN, an atomically thin sp2-hybridized sheet with a large band gap, to protect the Rh(111) metal surface. It is an ideal 2D platform to decouple the molecular precursor from the Rh(111) surface while maintaining the reactivity of Rh(111). We realize an Ullmann-like coupling of a planar biphenylene-based molecule, i.e., 1,8-dibromobiphenylene (BPBr2), on an hBN/Rh­(111) surface with an ultrahigh selectivity of the biphenylene dimer product, containing 4-, 6-, and 8-membered rings. The reaction mechanism, including electron wave penetration and the template effect of the hBN, is elucidated by combining low-temperature scanning tunneling microscopy and density functional theory calculations. Our findings are expected to play an essential role regarding the high-yield fabrication of functional nanostructures for future information devices.

Low-temperature molten salt synthesis and catalytic mechanism of CoS2/NC as an advanced bifunctional electrocatalyst

“…Furthermore, the carbon atoms adjacent to pyridinic N exhibit Lewis basicity and are commonly believed to be the active sites for ORR in NC materials. 39 Compared to the pyridinic nitrogen content in NC (21.14%), CoS 2 /NC with a higher proportion of pyridinic nitrogen (32.38%) exhibits superior ORR activity, which is in accordance with experimental observations (Table S1 †). Fig.…”

Gram‐Scale Mechanochemical Synthesis of Atom‐Layer MoS2 Semiconductor Electrocatalyst via Functionalized Graphene Quantum Dots for Efficient Hydrogen Evolution

“…These findings indicate that MoS 2 -1600 exhibits the highest hydrogen generation rate among the tested catalysts under the same applied overpotential, confirming the enhanced Volmer step kinetics as the HER pathway. [55,56] Additionally, MoS 2 -1600 demonstrated a significantly lower R ct (48 Ω) compared to MoS 2 -1200, MoS 2 -1400, and MoS 2 -1800 (Figure 5c), indicating enhanced conductivity and improved electron migration facilitated by the appropriate ball-milling speed during preparation.…”

Solvent Engineering of Oxygen‐Enriched Carbon Dots for Efficient Electrochemical Hydrogen Peroxide Production

“…Raman spectra were displayed in Figure 2b, the strong G bands at 1575 cm −1 and the extremely weak D band at 1320 cm −1 are noticed, respectively. [31,32] It is well known that plane vibrations of sp 2 -hybridized carbon atoms exert influence on the G band, and the D band is reflected in topological defects or sp 3 -hybridized carbon atoms. [33] Thus, the D to G intensity ratio (I D /I G ) is 0.080, 0.027, 0.011, 0.081, and 0.082 ranging from O-CDs-1 to O-CDs-5, respectively, giving an expression of the largest size of sp 2 domain of O-CDs-3 among all the O-CDs, which is consistent with the above TEM results.…”