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.