Activation of SO2 by N/Si+ and N/B Frustrated Lewis Pairs: Experimental and Theoretical Comparison with CO2 Activation.

The guanidine 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) and the substituted derivatives [TBD-SiR2 ]+ and TBD-BR2 reacted with SO2 to give different FLP-SO2 adducts. Molecular structures, elucidated by X-ray diffraction, showed some structural similarities with the analogous CO2 adducts. Thermodynamic stabilities were both experimentally evidenced and computed through DFT calculations. The underlying parameters governing the relative stabilities of the different SO2 and CO2 adducts were discussed from a theoretical standpoint, with a focus on the influence of the Lewis acidic moiety.