Lewis acidic salts of earth-abundant metals have recently gained attention as economically and environmentally advantageous alternatives to transition metal catalysts in chemical reactions. However, little is known about how altering the metal ion or the counterion of the Lewis acidic salt affects the nature of the salt-substrate binding and interaction modes during the activation process. To investigate this effect, we use a recent report on metal-mediated sulfur (VI) fluoride exchange (SuFEx) as a case study. In the report, calcium salts with bistriflimide counterions outperformed those with triflate and fluoride, and calcium outperformed magnesium, lithium, sodium, and potassium, revealing a clear ion-pair effect on SuFEx reactivity. In this work, density functional theory methods were used to uncover differences in the structural, energetic, and electronic properties of the SuFEx ground and transition states mediated by the calcium salts. The data gathered from our study provided key insights into the origins of the counterion effects and resulted in a new hypothesis for understanding reactivity differences across the Lewis acidic salts.

Metal ion-counterion effects on Lewis acid-mediated sulfur-fluoride exchange

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