Highly selective electrocatalytic dehydrogenation at low applied potential catalyzed by an Ir organometallic complex

Abstract

A homogeneous organometallic Ir complex was shown to catalyze the electro-oxidation of 4-methoxybenzyl alcohol to p-anisaldehyde at a very low applied potential with remarkably high selectivity and Faradaic efficiency. In the chemical catalysis, when stoichiometric oxidant and anionic base were used to separately accept electrons and protons, aldehyde selectivity was in agreement with electrolysis results.

Reversible catalytic dehydrogenation of alcohols for energy storage

“…Oxidants were surveyed with each catalyst over a relatively narrow range of chemical potentials in o-dichlorobenzene (o-DCB). All were greater than −0.13 V vs. the ferrocenium/ferrocene couple (Fc +/0 ), which is the peak oxidation potential (observed to be pseudoreversible at scan rates ≥ 1 V/s) that we reported for monodeprotonated 5, namely the neutral Ir-amido-amine complex [Ir(trop 2 DACH-1H)] 0 (30).…”

“…We regard separately extracting protons and electrons in a catalytic dehydrogenation reaction together with the microscopic reverse (29) (i.e., separately injecting protons and electrons to effect substrate hydrogenation) as fundamental in the development of a reversible alcohol dehydrogenation-hydrogenation electrocatalyst. It was clear at the outset that the possibility (30,31).…”

“…We now report our findings with 5 and 6 for alcohol dehydrogenation in terms of separately extracting protons and electrons through chemical catalysis results that used stoichiometric oxidants (e.g., ferrocenium) combined with a weak base (phenolate). We targeted separation of proton and electron transfer processes (instead of simultaneous transfer of protons and electrons to the same molecule, such as in BQ) to show the first necessary step in a broader strategy to transition Grützmacher's system to an electrocatalytic (i.e., electrodedriven) dehydrogenation and use such complexes as electrocatalysts (30). To verify the possibility of operating these catalysts in both directions, we have also studied the reverse reaction, separately injecting protons and electrons for aldehyde hydrogenation using 5 and 6 combined with stoichiometric reductants (e.g., cobaltocene) and weak conjugate acid (phenol).…”

Energy Production and Storage Promoted by Organometallic Complexes

“…Despite these advantages, there are still few examples of metal complexes employed as electrocatalysts for the oxidation of small organic molecules like CO, alcohols or sugars. These organometallic compounds are based both on precious metals like rhodium,, iridium, and ruthenium,, and on non‐precious metals like nickel , …”

“…A typical characteristic of these reactions is the need for a hydrogen acceptor, such as another ketone, olefin, or halocarbon compound. Bonitatibus et al replaced the hydrogen acceptor with an electrode to perform the 4‐methoxybenzyl alcohol oxidation to p ‐anisaldehyde with the Ir‐diaminodiolefin complex [Ir(trop 2 DACH)][OTf] [trop 2 DACH = N , N′ ‐bis(5 H dibenzo[ a,d ]cyclohepten‐5‐yl)‐1,2‐diaminocyclohexane] as electrocatalyst (Figure ) …”