Abstract
Frustrated Lewis pairs (FLPs) based on nitrogen heterocycles (pyridine, pyrazole, and imidazole) with a silane or germane group in the α-position of a nitrogen atom have been considered as potential molecules to sequestrate carbon dioxide. Three stationary points have been characterized in the reaction profile: a pre-reactive complex, an adduct minimum, and the transition state connecting them. The effect of external (solvent) or internal (hydroxyl group) electric fields in the reaction profile has been considered. In both cases, it is possible to improve the kinetics and thermodynamics of the complexation of CO2 by the FLP and favor the formation of adducts.
Highlights
Carbon dioxide, CO2, is a fascinating molecule
The first part analyzes the electronic properties of the isolated frustrated Lewis pairs (FLPs) and CO2 molecules
The isolated FLP considered in this work present a molecular electrostatic potential (MEP) suitable for simultaneous interactions of one of the nitrogen atoms as a Lewis base with the carbon atom of CO2 and the silane/germane group as a Lewis acid with one of the oxygen atoms of CO2
Summary
CO2, is a fascinating molecule. It is small, stable, and available in abundance; this apparently inoffensive compound has often its name written in capital letters next to the global warming phenomenon. It has been shown that carbon dioxide is able to form complexes with phosphines,[8−11] sulfur dioxide,[12] pyridine derivatives,[13−15] imidazole,[16−18] and other heterocycles.[19,20] It has been proved that CO2 can form adducts with carbenes[21−27] and frustrated Lewis pairs (FLPs),[28−33] some of them including silicon and germanium as Lewis acid centers.[34−36]. We explore the use of FLP based on Nheterocycles with a silane or germane group in the α-position of a nitrogen atom as potential molecules to form adducts with CO2 (Scheme 1). The nitrogen atom could act as a Lewis base (LB) and the silane or germane group as a Lewis acid (LA).[37−39] The intramolecular disposition of the LA and LB adds rigidity to these systems, which should minimize the entropic effects. We explore the effect on the kinetics and thermodynamics of the reaction by means of an electric field generated by a solvent (external) and a hydroxyl group in the heterocyclic ring
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