Why Does Activation of the Weaker CS Bond in CS₂ by P/N-Based Frustrated Lewis Pairs Require More Energy Than That of the CO Bond in CO₂? A DFT Study

Abstract

The sequestration of carbon disulfide (CS₂), a common pollutant in environmental systems, is of great importance due to its physical harm to human beings. Compared with CO₂ capture, that of CS₂ is much less developed. The use of P/N-based frustrated Lewis pairs (FLPs) has been proven, both experimentally and theoretically, to be an alternative strategy to efficiently sequestrate CO₂. Therefore, we pose the question of whether the analogue CS₂ could also be sequestrated by the same FLPs, given that the CS bond in CS₂ is weaker than the CO bond in CO₂. Herein, we carry out a thorough DFT study to theoretically examine this hypothesis for a series of P/N-based FLPs. Our results reveal unexpectedly higher reaction barriers in CS₂ capture by most of the P/N-based FLPs, although the bond dissociation energy of the CS bond in CS₂ (105.3 kcal mol^–1) is smaller than that of the CO bond in CO₂ (127.2 kcal mol^–1). The unexpected higher energy required for CS₂ activation can be rationalized by its larger bond distortion and its reverse bond polarization, as revealed by energy decomposition analysis and natural bond orbital analysis, respectively. Our findings could be helpful for experimentalists investigating the sequestration of CS₂ with P/N-based FLPs