Calcium triflimide, triflate, and fluoride salts have recently gained attention as cheap, abundant, and non-toxic Lewis acid catalysts. However, little is known about the mechanism of activation or the role of the counterions in these chemical reactions. Recent experiments show that calcium bistriflimide was effective in activating sulfur(VI) fluorides toward nitrogen-containing sulfur(VI) compounds via sulfur-fluoride exchange (SuFEx). However, significantly reduced yields were observed when calcium fluoride instead of bistriflimide, was used as the Lewis-acid activator, suggesting the non-innocent role of the counterion in facilitating calcium catalysis. In this work, density functional theory methods were used to compute and compare the SuFEx mechanism mediated by calcium fluoride to that of calcium bistriflimide. Structural, energetic, and electronic properties of the activated species are analyzed to reveal the origins of the counterion-induced differences in reactivity between Lewis-acidic calcium salts.

Investigating the role of the counterion in calcium-mediated sulfur-fluoride exchange

ACS Spring 2022

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