In a three-necked, round bottom flask bisimine (1.0 eq) was dissolved in THF (0.5 M) and the solution was heated to 70 °C. To this solution ZnCl2 (1.05 eq) was added and the mixture was stirred for 5 minutes. 2 M solution of HCl in diethyl ether (1.25 eq) and paraformaldehyde (1.3 eq) were added succesively and rapidly and stirred over night at 70 °C. The mixture was cooled to ambient temperature and concentrated and the resultant residue was then dissolved in DCM (50 mL) and washed with 2 M HCl (3 x 50mL) and brine (1 x 50mL) and brine of pH = 8 (1 x 50ml), with 2 times back-extracting with DCM. The organic solution was dried over MgSO4 and concentrated. The black crude oil was suspended in water and acetone (1:1) was added sodium iodide or sodium tetrafluoroborate (5 eq). The mixture was stirred for 4h at rt (sonicator to achieve homogenous suspension). The black mixture was extracted with DCM and dried over MgSO4. The solution was then concentrated under reduced pressure, the mixture was then added dropwise to diethyl ether or pentane with stirring. The carbene salts formed as solid, were then collected by simple filtration. Ketones 1a to 1z were synthesized according to the literature . Ketones 1aa to 1ae were used as received.