文摘
A series of monomeric (amino)(carboxy) radicals featuring carbonyl substituents with increasing electron-withdrawing properties (<b>3ab>, phenyl; <b>3bb>, 3,5-bis(trifluoromethyl)phenyl; <b>3cb>, perfluorophenyl; <b>3db>, heptafluoropropyl; <b>3eb>, 2H-pyrroliumyl) were synthesized in two or three steps from stable cyclic (alky)(amino)carbenes (CAACs). Although (amino)(carboxy) radicals had been previously considered as highly air-sensitive, some of these compounds feature half-lives of hours (<b>3db>), and even days (<b>3cb> and <b>3eb>) in well-aerated solutions. DFT calculations show that (amino)(carboxy) radicals evolve from C-centered radical to ambidentate C,O-radicals when increasing the electron-withdrawing properties of the carbonyl substituent. This is paralleled with a destabilization of the peroxide resulting from the addition of dioxygen to the radical. This latter reaction is even predicted to be endothermic for substituents with Hammett constant 蟽b>pb> > 0.2.