Hydrogenation of CO₂, Hydrogenocarbonate, and Carbonate to Formate in Water using Phosphine Free Bifunctional Iron Complexes

Abstract

The development of efficient and low-cost catalytic systems is important for the replacement of the robust noble metal complexes. A highly efficient, stable, phosphine-free, and easy-tosynthesize iron catalyst system for the reduction of CO 2 , hydrogenocarbonate, and carbonate in pure water is reported. In the presence of the bifunctional cyclopentadienone iron tricarbonyl Fe4a− d, the hydrogenation of carbonic derivatives proceeds in good yields with good catalyst productivity. Turnover numbers (TON) of up to 3343, 4234, and 40 for the hydrogenation of CO 2 , hydrogenocarbonate, and carbonate, respectively, to formate in pure water were achieved. For the CO 2 hydrogenation, a base was required, and triethanolamine emerged as the best one. DFT calculations rationalized the mechanism as well as the better performance of triethanolamine as a base.

(Cyclopentadienone)iron Complexes: Synthesis, Mechanism and Applications in Organic Synthesis

“…The complex 13 a exerted very high functional group tolerance (e. g., halide, ether, nitro, nitrile and trifluoromethyl groups) and significantly higher yields were obtained in shorter reaction times (Scheme 20A). Recently, the same group reported four new water‐soluble (diaminocyclopentadienone)iron complexes 14 a‐d (Figure 2), showing their ability to hydrogenate CO 2 with TONs up to 3540 [87] . These complexes show remarkably higher reactivity compared to an iron complex without any air‐sensitive pincer ligand or polydentate phosphine ligand.…”

Cyclopentadienone Iron Tricarbonyl Complexes-Catalyzed Hydrogen Transfer in Water

“…To develop water-soluble iron complexes, we selected a diaminocyclopentadienone ligand bearing ammonium functionalities [33]. The tetraamines 2 and 4 were prepared from diethyloxalate and N,N-dimethylpropylenediamine and N-aminopropylenemorpholine via an amidation followed by a reduction in good overall yield (93 and 95%, respectively).…”

“…The complexes Fe6 and Fe7 were synthesized in 48% and 76% yield by simple heating of the corresponding amino ligand with [Fe 2 (CO) 9 ] in refluxing toluene (Scheme 1). Finally, the water-soluble bifunctional iron complexes Fe4 and Fe5 bearing ionic frameworks were obtained in almost quantitative yields after a subsequent alkylation of the pendant amines with iodomethane (Scheme 1) [33]. These complexes were fully characterized by 1 H-, 13 C-NMR, and IR spectroscopies (see Supplementary Materials).…”

Experimental Evidence of syn H–N–Fe–H Configurational Requirement for Iron-Based Bifunctional Hydrogenation Catalysts

“…As far as the hydrogenation of CO bonds is concerned, this research field started to attract attention in the late 2000s, when the Knölker complex (a hydroxycyclopentadienyl iron dicarbonyl hydride) was demonstrated as the first well-defined iron catalyst for aldehyde/ketone hydrogenation, and diiminodiphosphine- and diaminodiphosphine-ligated iron complexes were established as the first iron-based catalytic systems for the asymmetric hydrogenation of ketones . Since these early reports, a variety of iron complexes, especially those supported by a pincer ligand, have been developed for improved catalytic efficiency , and/or enantioselectivity. , In the meantime, considerable efforts have been made to apply the iron-based hydrogenation strategy to the reduction of other carbonyl-containing substrates such as CO 2 /bicarbonates/carbonates, , esters, , amides, and oxamides …”