Waste Recycling: Ionic Liquid-Catalyzed 4-Electron Reduction of CO₂ with Amines and Polymethylhydrosiloxane Combining Experimental and Theoretical Study

Abstract

The acetate-based ionic liquids (ILs), e.g., [ n Bu4N]­OAc, have been developed for challenging 4-electron reduction of CO2 with amines and hydrosilane to afford aminals. Notably, polymethylhydrosiloxane, a cheap byproduct of the silicone industry, also works well as a reductant. Furthermore, an alternative pathway is rationally proposed via thorough density functional theory (DFT) study. In addition, the ILs play a surprisingly significant role through decreasing activation free energy. More importantly, the essence of being kinetically favorable with 4-electron reduction and thermodynamically favorable with 6-electron reduction is unveiled by DFT study, which guides us to successfully get 6-electron reductive products of CO2, i.e., methylamine. This work represents upgrading usage of both carbon and silicon wastes to valuable chemicals via IL catalysis.

Heterogeneous Organocatalysts for the Reduction of Carbon Dioxide with Silanes

“…Transfer hydrosilylation of aldehydes with silylformate as the "SiÀ H" surrogate. [41] Commonly, minor protocol modifications such as higher amount of hydrosilanes or increase in the temperature lead to formation of aminal [49] and N-methyl amine products. [50,51] In the context of reusing anthropogenic CO 2 to abate its contribution to global warming, the CO 2 utilization method should not only be effective but also sustainable, thus mitigating the environmental impact of the process.…”

“…These new synthetic methods toward amine derivatives offer more direct and atom‐efficient transformations under reaction conditions that are milder than those of existing processes. Commonly, minor protocol modifications such as higher amount of hydrosilanes or increase in the temperature lead to formation of aminal [49] and N ‐methyl amine products [50,51] …”

From CO2 activation to catalytic reduction: a metal-free approach

“…Therefore, only a few reports are currently available that address the metal-free reductive functionalization of CO 2 to aminals. 98,99 In 2015, Cantat and co-workers reported the rst metal-free catalyst for the 4e-reductive functionalization of CO 2 . 98 In the presence of 10 mol% TBD and CO 2 , secondary aromatic amines underwent reduction by PhSiH 3 at 80 C in acetonitrile, resulting in aminals with 98% yield (Scheme 30A).…”

Heteropolyacid ionic liquid heterogeneously catalyzed synthesis of isochromans via oxa-Pictet–Spengler cyclization in dimethyl carbonate

“…In the past few decades, the counter-cation precursors of some typical HPAsbased ionic liquids have been designed as pyridine, 1-methyl imidazole, and 1-methyl-2-pyrrolidinone, etc. [22][23][24][25][26][27] O 40 ]. We are making attempts to further develop this catalytic system for more valuable reactions, for example, the synthesis of isochromans from arylethanols and aldehydes via oxa-Pictet-Spengler cyclization (Scheme 1a).…”