N-Formylation of Amines with Carbon Dioxide and Hydrogen Catalyzed by Ionic Liquid-Assisted Ru Complexes

Abstract

The N-formylation reaction of various amines with CO 2 is a promising method to utilize CO 2 for the production of high value-added chemicals. Herein, an efficient Ru catalyst system consisting of Ru complex ([PPN][Ru(CO) 3 Cl 3 ]) and the ionic liquid 1-butyl-3-methylimidazolium hydrogen phosphate ([Bmim] 2 [HPO 4 ]), has been developed for the N-formylation reaction. Activity evaluation demonstrated that the catalyst system exhibited good to excellent yields of formamides under very mild conditions with the assistance of ionic liquids (ILs). Furthermore, the catalyst system could be reused at least five times with a slight loss of activity in N-formylmorpholine production. Further characterization by 1 H nuclear magnetic resonance (NMR), 13 C NMR, and density functional theory (DFT) calculations showed that the ILs ([Bmim] 2 [HPO 4 ]) could facilitate the adsorption of CO 2 by a concerted action of both cations and anions of the ILs to form phosphorus carbonate intermediate, thus effectively promoting the reaction. DFT calculations demonstrated that the formation of Ru−H was the first step, and then the CO 2 absorbed by [Bmim] 2 [HPO 4 ] inserted directly into Ru−H by cooperating with the Ru sites to form HCOO − species. After that, formate species dissociated from Ru catalysts and dehydrated to form formamides by the catalytic action of Ru complex and the basic IL.

Solvent-Assisted Ruthenium Complex Catalyzes Hydrogenation and the Reductive Amination of Carbon Dioxide

“…It can be seen that the catalytic system can be recycled at least five times with high selectivity to the formamide, revealing that the loss of activity was not significant. The slight decline of activity could be assigned to the possible blocking of Ru active sites by residual products in the consecutive runs as revealed previously …”

“…The slight decline of activity could be assigned to the possible blocking of Ru active sites by residual products in the consecutive runs as revealed previously. 84 Then, the combination of Ru-3 and TBAOAc was also explored for N-formylation of other secondary or primary amines. As shown in Table S5, morpholine gave low conversion in organic solvents (Table S5, entries 1 and 2), but showed excellent reaction activity in TBAOAc (Table S5, entry 3), which was consistent with the observation for ML hydrogenation.…”

Metal‐Catalyzed Carbonylation Reactions with CO2: An Update

“…The N ‐formylation reaction of amines 1 with CO 2 and H 2 was explored in 2021 by Hou and co‐workers in the presence of a Ru catalyst ([PPN][Ru(CO) 3 Cl 3 ]) (PPN, bis(triphenylphosphine)iminium) and the ionic liquid 1‐butyl‐3‐methylimidazolium hydrogen phosphate ([Bmim] 2 [HPO 4 ], Scheme 11). [20] The assistance of the ionic liquid improved the catalyst dispersion and CO 2 absorption, allowing the process to be run under very mild conditions, over a small range of aliphatic and aromatic primary/secondary amines 1 and granted a good degree of reusability of the catalytic system. Experimental NMR studies and DFT calculations elucidated the role of ([Bmim] 2 [HPO 4 ]), promoting the adsorption of CO 2 by a concerted action of both ions for the formation of a phosphorus carbonate adduct 27 , being the effective carbonylating species.…”

Ruthenium Single-Atom Anchored in Polyoxometalate-Ionic Liquids for N-Formylation of Amines with CO2 and H2

“…Based on our previous research work on CO 2 conversion, , we developed an efficient and highly stable binary IL catalytic system, consisting of ruthenium single-atom substituted Keggin-type POM IL (Ru-POM-IL) and 1-butyl-3-methyl-imidazolium acetate (BMImOAc). Notably, the introduction of ruthenium into the framework of POMs can construct POM-stabilized SACs, and the oxygen-enriched environment of POMs can play as “inorganic ligands” to coordinate with the ruthenium single atom, offering highly stable catalysts.…”