Selective Oxygen Atom Insertion into an Aryl–Palladium Bond

The chemistry of a palladium­(II) complex containing both an alkyl– and an aryl–palladium bond is reported. The reaction of [Pd­(CH2CMe2C6H4)­(MesNCHCHNMes)] with bromine or iodine leads to reductive elimination of 1,1-dimethylcyclobutabenzene with formation of [PdX2(MesNCHCHNMes)] (X = Br, I). However, the reaction with hydrogen peroxide gives [Pd­(CH2CMe2C6H4O)­(MesNCHCHNMes)] by overall oxygen atom insertion into the aryl–palladium rather than the alkyl–palladium bond. This complex [Pd­(CH2CMe2C6H4O)­(MesNCHCHNMes)] reacts with bromine, iodine, or hydrogen peroxide to give 3,3-dimethyl-2,3-dihydrobenzofuran and the corresponding complex [PdX2(MesNCHCHNMes)]. The mechanisms of reaction and basis for selectivity are discussed. The results support the view that oxygen atom insertion is a mechanistically viable pathway for selective catalytic oxidation of hydrocarbons by the green oxidant hydrogen peroxide.