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We report the synthesis, characterization, and electrocatalytic water oxidation activity of two cobalt complexes, (6-FP)Co(NO₃)₂ (1) (6-FP = 8,8′-(1,2-phenylene)diquinoline) and (5-FP)Co(NO₃)₂ (2) (5-FP = 1,2-bis(N-7-azaindolyl)benzene), containing “capping arene” bidentate ligands with nitrogen atom donors. The cobalt complexes 1 and 2 were supported on ordered mesoporous carbon (OMC) by π–π stacking, resulting in heterogenized cobalt materials 6-FP-Co-OMC-1 and 5-FP-Co-OMC-2, respectively, and studied for electrocatalytic water oxidation. We find that 6-FP-Co-OMC-1 exhibits an overpotential of 355 mV for a current density of 10 mA cm⁻² and a turnover frequency (TOF) of ∼0.53 s–1 at an overpotential of 400 mV at pH 14. 6-FP-Co-OMC-1 exhibits activity that is ∼1.6 times that of 5-FP-Co-OMC-2, which gives a TOF of 0.32 s⁻¹ at 400 mV overpotential. The structural stability of the single-atom Co site was demonstrated for 6-FP-Co-OMC-1 using X-ray absorption spectroscopy for the molecular complex supported on OMC, but slow degradation in catalyst activity can be attributed to eventual formation of Co oxide clusters. DFT computations of electrocatalytic water oxidation using the molecular complexes as models provide a description of the catalytic mechanism. These studies reveal that the mechanism for O–O bond formation involves an intermediate Coᴵⱽ oxo complex that undergoes an intramolecular reductive O–O coupling to form a Coᴵᴵ–OOH species. Further, the calculations predict that the molecular 6-FP-Co structure is more active for electrocatalytic water oxidation than 5-FP-Co, which is consistent with experimental studies of 6-FP-Co-OMC-1 and 5-FP-Co-OMC-2, highlighting the possibility that the ligand structure influences the catalytic activity of the supported molecular catalysts.

We show how to improve the yield of MeX from CH4 activation catalysts from 12% to 90% through the use of “capping arene” ligands. Four (FP)RhIII(Me)(TFA)2 {FP = “capping arene” ligands, including 8...

Hydrogen–deuterium exchange (H/D exchange) is a method commonly used for studying catalytic activation of C–H(D) bonds by transition metal complexes. In this study, a series of additives were studi...

Arene alkenylation is commonly achieved by late transition metal-mediated C(sp2)–C(sp2) cross-coupling, but this strategy typically requires prefunctionalized substrates (e.g., with halides or pseu...

Oxidative addition and reductive elimination reactions are central steps in many catalytic processes, and controlling the energetics of reaction intermediates is key to enabling efficient catalysis. A series of oxidative addition and reductive elimination reactions using (RPNP)RhX complexes (R = tert-butyl, isopropyl, mesityl, phenyl; X = Cl, I) was studied to deduce the effect of the size of the phosphine substituents. Using (^RPNP)RhCl as the starting material, oxidative addition of MeI was observed to produce (^RPNP)Rh(Me)(I)Cl, which was followed by reductive elimination of MeCl to form (^RPNP)RhI. The thermodynamics and kinetics vary with the identity of the substituent R on phosphorus of the PNP ligand. The presence of large steric bulk (e.g., R = tert-butyl, mesityl) on the phosphine favors Rh(I) in comparison to the presence of two smaller substituents (e.g., R = isopropyl, phenyl). An Eyring plot for the oxidative addition of MeI to (^(tBu)PNP)RhCl in THF-d₈ is consistent with a polar two-step reaction pathway, and the formation of [(^(tBu)PNP)Rh(Me)I]I is also consistent with this mechanism. DFT calculations show that the steric bulk affects the reaction energies of addition reactions which generate six-coordinate complexes by tens of kcal mol⁻¹. The ligand steric bulk is calculated to have a reduced effect (a few kcal mol⁻¹) on S_N2 addition barriers, which only require access to one side of the square plane.

For many years, the development of new methods and catalytic processes for the functionalization of C–H bonds has been among the primary challenges in the field of synthetic chemistry. The selective functionalization of light alkanes offers the possibility of expanded and more efficient use of natural gas, as the functionalization of larger hydrocarbons (e.g., long chain alkanes or arenes) could afford less expensive processes that are more environmentally benign as well as access to entirely new compounds, and the selective C–H functionalization of more complex organic compounds offers strategies for improved routes to prepare high-value fine chemicals.