Recent Advances on CO2 Utilization as C1 Building Block in C-N and C-O Bond Formation

Direct Synthesis of N-formamides by Integrating Reductive Amination of Ketones and Aldehydes with CO2 Fixation in a Metal-Organic Framework

Formamides are important feedstocks for the manufacture of many fine chemicals. State-of-the-art synthesis of formamides relies on the use of an excess amount of reagents, giving copious waste and thus poor atom-economy. Here, we report the first example of direct synthesis of N-formamides by coupling two challenging reactions, namely reductive amination of carbonyl compounds, particularly biomass-derived aldehydes and ketones, and fixation of CO2 in the presence of H2 over a metal-organic framework supported ruthenium catalyst, Ru/MFM-300(Cr). Highly selective production of N-formamides has been observed for a wide range of carbonyl compounds. Synchrotron X-ray powder diffraction reveals the presence of strong host-guest binding interactions via hydrogen bonding and parallel-displaced π⋅⋅⋅π interactions between the catalyst and adsorbed substrates facilitating the activation of substrates and promoting selectivity to formamides. The use of multifunctional porous catalysts to integrate CO2 utilisation in the synthesis of formamide products will have a significant impact in the sustainable synthesis of feedstock chemicals.

Catalytic reduction of carbon dioxide by a zinc hydride compound, [Tptm]ZnH, and conversion to the methanol level

The zinc hydride compound, [Tptm]ZnH, may achieve the reduction of CO₂ by (RO)₃SiH (R = Me, Et) to the methanol oxidation level, (MeO)_xSi(OR)_4-x, via the formate species, HCO₂Si(OR)₃. However, because insertion of CO₂ into the Zn-H bond is more facile than insertion of HCO₂Si(OR)₃, conversion of HCO₂Si(OR)₃ to the methanol level only occurs to a significant extent in the absence of CO₂.

Borane-Trimethylamine Complex as a Reducing Agent for Selective Methylation and Formylation of Amines with CO2

We report herein that a borane-trimethylamine complex worked as an efficient reducing agent for the selective methylation and formylation of amines with 1 atm CO₂ under metal-free conditions. 6-Amino-2-picoline serves as a highly efficient catalyst for the methylation of various secondary amines, whereas in its absence, the formylation of primary and secondary amines was achieved in high yield with high chemoselectivity. Mechanistic studies suggest that the 6-amino-2-picoline-borane catalytic system operates like an intramolecular frustrated Lewis pair to activate CO₂.

Ni-Catalyzed Direct Carboxylation of an Unactivated C-H Bond with CO2

The transition-metal-catalyzed direct carboxylation of an unactivated C-H bond is rarely reported, and no example of catalysis using abundant and cheap nickel has been reported. In this work, the first Ni-catalyzed direct carboxylation of an unactivated C-H bond under an atmospheric pressure of CO₂ is reported. This method affords moderate to high carboxylation yields of various methyl carboxylates under mild conditions. Preliminary mechanistic studies reveal that a Ni(0)-Ni(II)-Ni(I) catalytic cycle may be involved in this reaction.

Ruthenium-Catalyzed Synthesis of Cyclic and Linear Acetals by the Combined Utilization of CO2 , H2 , and Biomass Derived Diols

Herein a transition-metal catalyst system for the selective synthesis of cyclic and linear acetals from the combined utilization of carbon dioxide, molecular hydrogen, and biomass derived diols is presented. Detailed investigations on the substrate scope enabled the selectivity of the reaction to be largely guided and demonstrated the possibility of integrating a broad variety of substrate molecules. This approach allowed a change between the favored formation of cyclic acetals and linear acetals, originating from the bridging of two diols with a carbon-dioxide based methylene unit. This new synthesis option paves the way to novel fuels, solvents, or polymer building blocks, by the recently established "bio-hybrid" approach of integrating renewable energy, carbon dioxide, and biomass in a direct catalytic transformation.

Scalable direct N-methylation of drug-like amines using 12CO2/13CO2 by simple inorganic base catalysis

With the growing urgency of potential catastrophic climate changes due to anthropogenic CO₂ emissions, numerous efforts have been devoted to development of synthetic protocols using CO₂ as a building block in organic reactions, but the general applicability to complex drug-like substrates remains a challenge. We develop a general protocol for scalable direct N-methylation of a wide-scope drug-like amines using CO₂ and polymethylhydrosiloxane-a nontoxic, aerobically-stable hydrosilane considered as an industrial waste-via simple inorganic base catalysis. A rare application of the Sabatier principle in organic chemistry led to the discovery of cheap, nontoxic K₃PO₄ as an efficient catalyst. Preparations of a wide-scope drug-like amines with carbon-isotope label were also successfully achieved, enabling direct use of CO₂ in studies of drug absorption, distribution, metabolism and excretion.