The utilization of carbon dioxide (CO 2) as feedstock for chemical industries is gaining interest as a sustainable alternative to nonrenewable fossil resources. However, CO 2 reduction is necessary to increase its energy content. Hydrosilane is a potential reducing agent that exhibits excellent reactivity under ambient conditions. CO 2 hydrosilylation yields versatile products such as silylformate and methoxysilane, whereas formamides and N-methylated products are obtained in the presence of amines. In these transformations, organocatalysts are considered as the more sustainable choice of catalyst. In particular, heterogeneous organocatalysts featuring precisely designed active sites offer higher efficiency due to their recyclability. Herein, an overview is presented of the current development of basic organocatalysts immobilized on various supports for application in the chemical reduction of CO 2 with hydrosilanes, and the potential active species parameters that might affect the catalytic activity are identified.
Various organocatalysts are developed to accelerate the carbon dioxide utilisation as feedstock to value-added organic chemicals synthesis with silanes as strategic reducing agents.
Formate
salts were found to be active and selective homogeneous
catalysts for the hydrosilylation of CO2. Counter cations
and solvents strongly affected their catalytic activity. The use of
toluene as a solvent rendered the recyclable catalyst system. Lewis
basic polar solvents such as N-methylpyrrolidone
and dimethyl sulfoxide significantly accelerated the reaction. The
turnover number approached up to 1800. Analyses of the Fourier-transform
infrared spectroscopy and in situ 1H nuclear magnetic resonance
spectra suggested that the catalysis proceeds via electron donation
from the solvent to hydrosilane, thereby accelerating the hydride
transfer step.
A heterogeneous formate anion catalyst for the transformative reduction of carbon dioxide (CO2) based on a polystyrene and divinylbenzene copolymer modified with alkylammonium formate was prepared from a widely available anion exchange resin. The catalyst preparation was easy and the characterization was carried out by using elemental analysis, Fourier transform infrared (FTIR) spectroscopy, X‐ray photoelectron spectroscopy (XPS), and solid‐state 13C cross‐polarization/magic‐angle spinning nuclear magnetic resonance (13C CP/MAS NMR) spectroscopy. The catalyst displayed good catalytic activity for the direct reduction of CO2 with hydrosilanes, tunably yielding silylformate or methoxysilane products depending on the hydrosilanes used. The catalyst was also active for the reductive insertion of CO2 into both primary and secondary amines. The catalytic activity of the resin‐supported formate can be predicted from the FTIR spectra of the catalyst, probably because of the difference in the ionic interaction strength between the supported alkylammonium cations and formate anions. The ion pair density is thought to influence the catalytic activity, as shown by the elemental and solid‐state 13C NMR analyses.
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