Inside the glovebox, the tetrafluoroborate salt was suspended in THF (0.05 M) and NaH (4 equiv) was added in plus catalytic amount (spatula tip) of KOtBu in a Schlenk tube. The mixture was taken outside the glovebox and sonicated at room temperature for 4 hours, then the mixture was brought back inside the glovebox. After removal of the solid by-products by filtration through a pad of celite on a frit. The solution was concentrated directly afforded the desired carbenes.