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When irradiated with blue light in the presence of a Lewis base (L), [CpW(CO) 3 ] 2 undergoes metal–metal bond cleavage followed by a disproportionation reaction to form [CpW(CO) 3 L] + and [CpW(CO) 3 ] − . Here, we show that in the presence of pyridinium tetrafluoroborate, [CpW(CO) 3 ] − reacts further to form a metal hydride complex CpW(CO) 3 H. The rection was monitored through in situ photo 1 H NMR spectroscopy experiments and the mechanism of light-driven hydride formation was investigated by determining quantum yields of formation. Quantum yields of formation of CpW(CO) 3 H correlate with I −1/2 (I = photon flux on our sample tube), indicating that the net disproportionation of [CpW(CO) 3 ] 2 to form the hydride precursor [CpW(CO) 3 ] − occurs primarily through a radical chain mechanism. 

Rotating disc electrode (RDE) voltammetry has been widely adopted for the study of heterogenized molecular electrocatalysts for multi-step fuel-forming reactions but this tool has never been comprehensively applied to their homogeneous analogues. Here, the utility and limitations of RDE techniques for mechanistic and kinetic analysis of homogeneous molecular catalysts that mediate multi-electron, multi-substrate redox transformations are explored. Using the ECEC′ reaction mechanism as a case study, two theoretical models are derived based on the Nernst diffusion layer model and the Hale transformation. Current–potential curves generated by these computational strategies are compared under a variety of limiting conditions to identify conditions under which the more minimalist Nernst Diffusion Layer approach can be applied. Based on this theoretical treatment, strategies for extracting kinetic information from the plateau current and the foot of the catalytic wave are derived. RDEV is applied to a cobaloxime hydrogen evolution reaction (HER) catalyst under non-aqueous conditions in order to experimentally validate this theoretical framework and explore the feasibility of RDE as a tool for studying homogeneous catalysts. Crucially, analysis of the foot-of-the-wave via this theoretical framework provides rate constants for elementary reaction steps that agree with those extracted from stationary voltammetric methods, supporting the application of RDE to study homogeneous fuel-forming catalysts. Finally, obstacles encountered during the kinetic analysis of cobaloxime, along with the voltammetric signatures used to diagnose this reactivity, are discussed with the goal of guiding groups working to improve RDE set-ups and help researchers avoid misinterpretation of RDE data.