Graphite-Conjugated Rhenium Catalysts for Carbon Dioxide Reduction

Condensation of <i>fac</i>-Re­(5,6-diamino-1,10-phenanthroline)­(CO)₃Cl to <i>o</i>-quinone edge defects on graphitic carbon surfaces generates graphite-conjugated rhenium (GCC-Re) catalysts that are highly active for CO₂ reduction to CO in acetonitrile electrolyte. X-ray photoelectron and X-ray absorption spectroscopies establish the formation of surface-bound Re centers with well-defined coordination environments. GCC-Re species on glassy carbon surfaces display catalytic currents greater than 50 mA cm⁻² with 96 ± 3% Faradaic efficiency for CO production. Normalized for the number of Re active sites, GCC-Re catalysts exhibit higher turnover frequencies than that of a soluble molecular analogue, <i>fac</i>-Re­(1,10-phenanthroline)­(CO)₃Cl, and turnover numbers greater than 12,000. In contrast to the molecular analogue, GCC-Re surfaces display a Tafel slope of 150 mV/decade, indicative of a catalytic mechanism involving rate-limiting one-electron transfer. This work establishes graphite-conjugation as a powerful strategy for generating well-defined, tunable, heterogeneous electrocatalysts on ubiquitous graphitic carbon surfaces

Catalytic Methane Monofunctionalization by an Electrogenerated High-Valent Pd Intermediate

Electrophilic high-valent metal ions are potent intermediates for the catalytic functionalization of methane, but in many cases, their high redox potentials make these intermediates difficult or impossible to access using mild stoichiometric oxidants derived from O₂. Herein, we establish electrochemical oxidation as a versatile new strategy for accessing high-valent methane monofunctionalization catalysts. We provide evidence for the electrochemical oxidation of simple PdSO₄ in concentrated sulfuric acid electrolytes to generate a putative Pd₂^III,III species in an all-oxidic ligand field. This electrogenerated high-valent Pd complex rapidly activates methane with a low barrier of 25.9 (±2.6) kcal/mol, generating methanol precursors methyl bisulfate (CH₃OSO₃H) and methanesulfonic acid (CH₃SO₃H) via concurrent faradaic and nonfaradaic reaction pathways. This work enables new electrochemical approaches for promoting rapid methane monofunctionalization

Helical Ribbons for Molecular Electronics

We describe the design and synthesis of a new graphene ribbon architecture that consists of perylenediimide (PDI) subunits fused together by ethylene bridges. We created a prototype series of oligomers consisting of the dimer, trimer, and tetramer. The steric congestion at the fusion point between the PDI units creates helical junctions, and longer oligomers form helical ribbons. Thin films of these oligomers form the active layer in n-type field effect transistors. UV–vis spectroscopy reveals the emergence of an intense long-wavelength transition in the tetramer. From DFT calculations, we find that the HOMO–2 to LUMO transition is isoenergetic with the HOMO to LUMO transition in the tetramer. We probe these transitions directly using femtosecond transient absorption spectroscopy. The HOMO–2 to LUMO transition electronically connects the PDI subunits with the ethylene bridges, and its energy depends on the length of the oligomer