Electrocatalytic Transfer Hydrogenation of 1‐Octene with [(tBuPCP)Ir(H)(Cl)] and Water

Electrocatalytic hydrogenation of 1‐octene as non‐activated model substrate with neutral water as H‐donor is reported, using [(tBuPCP)Ir(H)(Cl)] (1) as the catalyst, to form octane with high faradaic efficiency (FE) of 96 % and a kobs of 87 s−1. Cyclic voltammetry with 1 revealed that two subsequent reductions trigger the elimination of Cl− and afford the highly reactive anionic Ir(I) hydride complex [(tBuPCP)Ir(H)]− (2), a previously merely proposed intermediate for which we now report first experimental data by mass spectrometry. In absence of alkene, the stoichiometric electrolysis of 1 in THF with water selectively affords the Ir(III) dihydride complex [(tBuPCP)Ir(H)2] (3) in 88 % FE from the reaction of 2 with H2O. Complex 3 then hydrogenates the alkene in classical fashion. The presented electro‐hydrogenation works with extremely high FE, because the iridium hydrides are water stable, which prevents H2 formation. Even in strongly alkaline conditions (Bu4NOH added), the electro‐hydrogenation of 1‐octene with 1 also proceeds cleanly (89 % FE), suggesting a highly robust process that may rely on H2O activation, reminiscent to transfer hydrogenation pathways, instead of classical H+ reduction. DFT calculations confirmed oxidative addition of H2O as a key step in this context. We report the quantitative electro‐hydrogenation of unactivated alkenes with H2O in neutral or even alkaline conditions. Electro‐hydrogenation is typically driven by H+ reduction in acidic media to generate reactive metal‐hydrides, which then either hydrogenate or react with H+ to liberate H2 in a parasitic process. Our work shows that H2 evolution can be suppressed by forming metal‐hydrides via oxidative addition of H2O instead of H+ reduction.