The effects of ionic liquids on the thermodynamics of H2 activation by frustrated Lewis pairs: a density functional theory study

TL;DR

This study uses density functional theory to analyze how ionic liquids influence hydrogen activation by frustrated Lewis pairs, revealing that ILs generally promote H-H cleavage but affect other steps differently depending on FLP type.

Contribution

It provides a detailed thermodynamic analysis of FLP-H2 activation in ionic liquids, highlighting the differential effects based on FLP structure and solvent environment.

Findings

ILs make H-H cleavage more thermodynamically favorable.

ILs disfavor proton and hydride attachment steps.

Intra-molecular FLPs are more affected by ILs than inter-molecular FLPs.

Abstract

Nowadays, hydrogen activation by frustrated Lewis pairs (FLPs) and their applications have been demonstrated to be one of emerge research topics in the field of catalysis. Previous studies have shown that the thermodynamics of these reaction is determined by electronic structures of FLPs and solvents. Herein, we investigated the systems consisting of typical FLPs and ionic liquids (ILs), which are well known by their large number of types and excellent solvent effects. The density functional theory (DFT) calculations were performed to study the thermodynamics for H2 activation by both inter- and intra-molecular FLPs, as well as the individual components. The results show that the computed overall Gibbs free energies in ILs are more negative than that computed in toluene. Through the thermodynamics partitioning, we find that ILs favor the H-H cleavage elemental step, while disfavored the elemental steps of proton attachment, hydride attachment and zwitterionic stabilization. Moreover, the results show that these effects are strongly dependent on the type of FLPs, where intra-molecular FLPs are more effected compared to the inter-molecular FLPs.