Proton Independent Electrocatalytic Transfer Hydrogenation of Styrene with [(tBuPCP)Ir(H)(Cl)] and Water

08 March 2022, Version 1
This content is a preprint and has not undergone peer review at the time of posting.


A new pathway of electrocatalytic transfer hydrogenation with neutral water as the H-donor was discovered using [(tBuPCP)Ir(H)(Cl)] (1) as the catalyst and styrene as a model substrate in THF electrolyte. Cyclic voltammetry experiments with 1 revealed that two subsequent reductions at –2.55 and –2.84 V vs. Fc+/Fc trigger the elimination of Cl– and afford the highly reactive anionic Ir(I) hydride complex [(tBuPCP)Ir(H)]– (2). The identity of 2 and its reactivity were further investigated by LIFDI-MS, which confirmed 2 as reactive species in the alkene hydrogenation cycle. Bulk electrolysis and chronoamperometry for electro-hydrogenation of styrene established ethylbenzene as the only product, formed with high faradaic efficiency of 96% and a turnover frequency of 1670 h–1 at an electrolysis potential of –3.1 V, with insignificant H2 formation. Importantly, the electro-hydrogenation performance of 1 remained constant upon addition of KOH to the electrolyte, which suggests a reaction mechanism that is independent of free H+. Instead, the reactive Ir-hydrides are regenerated by oxidative addition of H2O to the complex, which creates a reaction cascade that is reminiscent of metal-hydride formation in classical transfer hydrogenation systems. As such, the herein presented study on electrocatalytic transfer hydrogenation (e-TH) with H2O as the H-donor is different from the plethora of other electro-hydrogenation studies that operate via H+ reduction, often in low-pH electrolyte. These findings may inspire the general, pH independent use of H2O as H-donor in conjunction with electrochemistry, to replace isopropanol or formate as intrinsically reducing H-donors in the many existing examples of classical transfer hydrogenation.


Electrocatalytic Hydrogenation
Pincer Complex

Supplementary materials

Supporting Information
Supporting information containing experimental details, synthesis procedures, relevant NMR data, additional electrochemical experiments and LIFDI-MS details.


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