Electrocatalytic Transfer Hydrogenation of 1-Octene with [( tBu PCP)Ir(H)(Cl)] and Water.

Electrocatalytic hydrogenation of 1-octene as non-activated model substrate with neutral water as H-donor is reported, using [( tBu PCP)Ir(H)(Cl)] (1) as the catalyst, to form octane with high faradaic efficiency (FE) of 96 % and a k obs 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 [( tBu PCP)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 [( tBu PCP)Ir(H) 2 ] (3) in 88 % FE from the reaction of 2 with H 2 O. 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 H 2 formation. Even in strongly alkaline conditions (Bu 4 NOH added), the electro-hydrogenation of 1-octene with 1 also proceeds cleanly (89 % FE), suggesting a highly robust process that may rely on H 2 O activation, reminiscent to transfer hydrogenation pathways, instead of classical H + reduction. DFT calculations confirmed oxidative addition of H 2 O as a key step in this context.