Mechanistic studies of electrocatalytic reactions play a crucial role in developing efficient electrocatalysts and solar-fuel devices. The foot of the wave analysis (FOWA) for cyclic voltammetry, recently developed by Saveánt and Costentin, provides a powerful means to evaluate the performance of molecular electrocatalysts. However, there is a considerable amount of confusion in the community on how to interpret FOWA in multielectron electrochemical reactions. Herein, we further expand their earlier models from the Nernstian region to all scenarios (i.e., including non-Nernstian behavior) and systematically examine individual parameters, such as formal potentials and reaction rate constants, to explore deeper insights and limitations. Detailed analysis from in silico voltammograms based on different mechanistic models reveals characteristic features of FOWA traces for different kinetic phenomena, which is useful to diagnose kinetic profiles and elucidate the limits of FOWA. The lessons learned from these analyses are further used to reconcile the discrepancy of rate constants determined by FOWA versus other methods, such as time-resolved spectroscopy, for molecular electrocatalysts that catalyze proton reduction or the reduction of CO 2 to CO. Such reconciliation demonstrates that electrochemical methods along with FOWA can serve as an alternative tool to determine kinetic information and probe mechanistic insights, which otherwise may be challenging and complicated to achieve by conventional methods. In addition, general guidelines and warnings are also presented to avoid potential errors or mishandling when using FOWA.
The combination of conventional transition-metal-catalyzed coupling (2 e process) and photoredox catalysis (1 e process) has emerged as a powerful approach to catalyze difficult cross-coupling reactions under mild reaction conditions. Reported is a palladium carbodicarbene (CDC) complex that mediates both a Suzuki-Miyaura coupling and photoredox catalysis for C-N bond formation upon visible-light irradiation. These two catalytic pathways can be combined to promote both conventional transition-metal-catalyzed coupling and photoredox catalysis to mediate C-H arylation under ambient conditions with a single catalyst in an efficient one-pot process.
The development of oxygen-tolerant H 2 -evolving catalysts plays a vital role for a future H 2 economy. For example, the [FeFe] hydrogenase enzymes are excellent catalyst for H 2 evolution but rapidly become inactivated in the presence of O 2 . The mechanistic details of the enzyme's inactivation by molecular oxygen still remain unclear. Here, two H 2 -evolving diiron complexes [Fe 2 (μ-SCH 2 NHCH 2 S)(CO) 6 ] (1 adt ) and [Fe 2 (μ-SCH 2 CH 2 CH 2 S)(CO) 6 ] (2 pdt ), inspired by the active site of [FeFe] hydrogenase, were investigated for their reactivity with molecular oxygen and reactive oxygen species. A one-electron reduced and oxygenated 1 adt species was identified and characterized spectroscopically, which can be directly generated by reacting with molecular oxygen and chemical reductants at room temperature but it is unstable and gradually decomposes. Interestingly, the whole process is reversible and the addition of protons can facilitate the deoxygenation process and prevent further degradation at room temperature. This new identification of intermediate species serves as a model for studying the reversible inactivation and degradation of oxygen-sensitive [FeFe] hydrogenases by O 2 , and provides chemical precedence for such processes. In comparison, the complex lacking the nitrogen bridgehead, 2 pdt , exhibits reduced reactivity towards O 2 in the presence of reductants, highlighting that the importance of the second coordination sphere on modulating the oxygenation processes. These results provide new directions to design molecular electrocatalysts for proton reduction operated at ambient conditions and the re-engineering of [FeFe] hydrogenases for improving oxygen tolerance. † Electronic supplementary information (ESI) available: Detailed experimental procedures and further spectroscopic and mechanistic studies. See ChemicalsBis(cyclopentadienyl)cobalt(II), bis(pentamethylcyclopentadienyl)cobalt(II), potassium superoxide, hydrogen peroxide (30% w/w in water) and 18 O 2 (97%) were purchased from Sigma-Aldrich. Chloroacetic acid (>99.0%), trichloroacetic acid (> 99.0%) and 3-chloroperbenzoic acid (mCPBA) were also obtained from Sigma-Aldrich. The molecular oxygen (99.9%) from Air Liquide Dalton Transactions PaperThis journal is
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