Base‐Free Dehydrogenation of Aqueous and Neat Formic Acid with Iridium(III) Cp*(dipyridylamine) Catalysts

Abstract

The selective dehydrogenation of formic acid by iridium(III) Cp*(dipyridylamine) catalysts is reported. The electron‐enriched catalyst [IrIIICp*{(4‐dimethylaminopyridin‐2‐yl‐κΝ)(pyridin‐2′‐yl‐κΝ)amine}(OSO3)] gave the best performances enabling the base free dehydrogenation of aqueous and neat formic acid. In both cases the reaction was selective with no carbon monoxide detectable. The IrIII complex demonstrated latent behavior, which may be of practical utility. Experimental results suggest an outer‐sphere interaction with the ligand.

Understanding the Deactivation Pathways of Iridium(III) Pyridine‐Carboxiamide Catalysts for Formic Acid Dehydrogenation

“…They exhibit high activity also under mild reaction conditions, and often operate in water and in the absence of any base and additive, which is essential for practical applications. High performances are frequently achieved via cooperativity between the metal center and suitable functionalities on the ancillary ligands [15, 21–24] . For example, the groups of Himeda and Fujita reported a variety of high‐performing iridium catalysts with pH‐responsive hydroxyl‐substituted bipyridine (TOF up to 14 000 h −1 at 90 °C), [25] bipyrimidine (12 000 h −1 at 60 °C), [26] and bisimidazole (34 000 h −1 at 80 °C) [27] ligands and combinations thereof, [13, 28] all of them function efficiently in aqueous solutions and in the absence of any base and additive.…”

“…Highp erformances are frequently achieved via cooperativity between the metal centera nd suitable functionalities on the ancillary ligands. [15,[21][22][23][24] For example, the groups of Himeda and Fujita reported av ariety of high-performing iridium catalysts with pH-responsive hydroxyl-substituted bipyridine (TOF up to 14 000 h À1 at 90 8C), [25] bipyrimidine( 12 000 h À1 at 60 8C), [26] and bisimidazole (34 000 h À1 at 80 8C) [27] ligands and combinationst hereof, [13,28] all of them function efficiently in aqueous solutionsa nd in the absence of any base and additive. One of the highest TOFs has been reported in 2015 by Li and co-workers, who developed exceedingly active iridium catalysts with N,N'-diimine ligands( TOF up to 487 500 h À1 at 90 8C).…”

Sustainable catalysis with fluxional acridine-based PNP pincer complexes

“…85 Formic acid is a promising H 2 carrier for its use in the transportation sector, however, most H 2 liberation systems from formic acid require solvents and/or additives, 86,87 which decreases the practical applicability, with only handful reports for neat FA dehydrogenation. [88][89][90] Complex 4 showed excellent activity in additive-free neat FA dehydrogenation achieving turnover frequencies (TOFs) over 3000 h -1 . The catalyst is also effective in producing H 2 from commercially available low-grade 85% FA, and at the same time, can also generate high-pressure H 2 /CO 2 from neat FA (100 bars).…”

An Update on Formic Acid Dehydrogenation by Homogeneous Catalysis

“…Williams's group described an iridium−NP complex 4 (Figure ), which can continue to work up to 4 months and provide a TON of 2,160,000 under the neat FA condition . Fischmeister and co‐workers also reported an iridium complex with Cp*(dipyridylamine) ligand to selective decompose aqueous and neat FA under the base‐free conditions to give TOF of 13,292 h −1 at 100 °C . More discussions will be provided in section 3.…”