The Z-selective semi-reduction of alkyne using CoBr2/6,6'-dimethylbipyridine (Conditions C) was also investigated. Similarly, CV studies with increasing concentration of ligand were also performed (Figure ). With such a system, no distinct peak separation was observed at 1:1 ratio of CoBr2/ligand. However, upon the increasing concentration of the ligand, a notable cathodic peak shift was observed where the reduction peak potential becomes less negative as a function of increasing ligand concentration. The shifted regions were labeled as predominantly one-electron reduction of monoligated and bisligated Co(II), respectively (Figure , step A). Using a mixture of 1:1.5 ratio of CoBr2/ligand (predominantly monoligated, and similar to the ratio in the reaction conditions), the effect of HFIP and alkyne addition (Figure ) was studied. The addition of 1 equivalent of HFIP showed a shift in the peak, denoting a chemical step that generates a new electroactive cobalt intermediate proposed as Co(III)-H (Figure , step B). The addition of alkyne to this mixture resulted in an increase in cathodic peak current with reduction potential similar to the active catalyst. This denotes a chemical reaction of the cobalt-hydride intermediate with the alkyne accompanied by regeneration of the monoligated cobalt(II) catalyst (Figure , steps F to H). Computational analysis corroborated this proposed mechanism of proton migration from HFIP to the coordinated alkyne (Figure -10, step G) as it demonstrated feasible energetics. The barrier for such a process is notably low (∆G ‡ =6.2 kcal/mol) as it proceeds through a completely concerted mechanism (see SI for details). These values provide support for step G of the alkyne reduction catalytic cycle.