Impact of Protic Ligands in the Ir-Catalyzed Dehydrogenation of Formic Acid in Water

Abstract

New Ir-IPr complexes featuring a variety of chelate ligands, some of them featuring NH moieties, were synthesized. These complexes proved to be efficient catalysts for the dehydrogenation of formic acid in DMF and H 2 O. The dehydrogenation rates were dependent on the nature of the ligands that accompany IPr in the coordination sphere of the metal. In fact, complexes that contain protic ligands, namely, [Ir(8-aminoquinoline)(H) 2 (IPr)(PPhMe 2)]BF 4 and [Ir(CH 3 CN)(2-phenylimidazole)(H)(IPr)(PPhMe 2)]BF 4 showed the best activities in H 2 O. The former, which presents an NH 2 group bound to the Ir center, is the most active (in H 2 O) of the catalysts presented in this work, and can be recycled up to 10 times without an apparent loss of activity. This behavior may be attributed to the robust ligand system and, likely, to its ability to establish outer-sphere interactions. This postulation is supported by the fact that complex [Ir(8dimethylaminoquinoline)(H) 2 (IPr)(PPhMe 2)]BF 4 , which features an-NMe2 instead of an-NH2 donor group, gives rise to a strikingly lower catalytic activity.

Hydrogen production from formic acid catalyzed by a phosphine free manganese complex: investigation and mechanistic insights

“…In the past decade, noble metal complexes with heterocyclic ligands, especially those bearing an N-H moiety, showed high efficiency in the DH of formic acid [24][25][26][27] or the hydrogenation of carbon dioxide. 28,29 In this context, a panel of manganese complexes was synthesized and tested for the DH of FA (Table 1).…”

Dehydrogenation of Formic Acid Catalyzed by Water‐Soluble Ruthenium Complexes: X‐ray Crystal Structure of a Diruthenium Complex

“…We demonstrated that the N‐H moieties of en and AmQ ligands play a crucial role in the initial activation of formic acid to facilitate the transfer hydrogenation of furfural to furfuryl alcohol, which eventually transformed to LA , . Very recently, Oro et al reported Ir‐NHC (NHC = N‐heterocyclic carbene) based complexes for formic acid dehydrogenation in DMF and H 2 O . Though these complexes exhibit only moderate activity in H 2 O, the initial TOF is highest (790 h –1 ) for the Ir‐NHC‐AmQ complex.…”

“…[17,18] Very recently, Oro et al reported Ir-NHC (NHC = N-heterocyclic carbene) based complexes for formic acid dehydrogenation in DMF and H 2 O. [14] Though these complexes exhibit only moderate activity in H 2 O, the initial TOF is highest (790 h -1 ) for the Ir-NHC-AmQ complex. Moreover, a significant quenching of the catalytic activity of Ir-NHC complex was observed when AmQ was replaced with 8-(N,N-dimethylamino)quinoline (DMAmQ), suggesting the crucial role of NH moiety of AmQ in enhancing the catalytic activity for formic acid dehydrogenation in H 2 O. Envisioned by our previous observations, herein, we investigated in detail the dehydrogenation of formic acid over Ruarene complexes containing various nitrogen-donor chelating ligands and demonstrated the crucial role of these ligands on the formic acid dehydrogenation process.…”

A Precious Catalyst: Rhodium‐Catalyzed Formic Acid Dehydrogenation in Water

“…In many scenarios, the reaction is performed in water, a benign and green solvent, but many other well‐working solvent systems are known to literature, including the direct dehydrogenation of neat FA . The continuous attempts to elucidate the mode of operation of various catalysts give detailed insight into the mechanistic processes during the reaction …”

“…Especially prolific are bidentate nitrogen donor ligands,[15b], [15f], phosphane containing structures, and pincer ligands. [13d], However, for a large‐scale application, first‐row transition metal catalysts are more attractive, for many reasons but mainly because they are cheap and abundant. The development of working iron catalysts is an essential step in this direction .…”