Catalytic oxygenation of olefin with dioxygen and tetra-t-butylphthalocyanine complexes in the presence of sodium borohydride

Catalytic oxygenation of styrene with dioxygen was performed by tetra-t-butylphthalocyanine complexes of manganese (III), iron(III), and cobalt(II) in the presence of sodium borohydride using ethanol as a solvent. The yield of 1-phenylethanol increased with the passage of time in the case of the manganese(III) and iron(III) complexes, but an induction period appeared in the case of the cobalt(II) complex. The initial reaction rate was 2.8 × 10^-3 or 3.4 × 10^-2 mmol min^-1 for the reaction catalyzed by the manganese(III) or cobalt(II) complex respectively. No oxygenation product was formed in anaerobic ethanol with any of the complexes, but ethylbenzene was formed exclusively in the presence of the cobalt(II) complex. A radical scavenger, 2,2,6,6-tetramethylpiperidine-1-oxyl, inhibited the reaction considerably with the manganese(III) or iron(III) complex, but inhibited the reaction slightly with the cobalt(II) complex. The amount of oxygenation product from α-methylstyrene was larger than that from styrene in the case of the manganese(III) and iron(III) complexes, but the amount of oxygenation product from α-methylstyrene was almost the same as that from styrene in the case of the cobalt(II) complex. A radical mechanism is proposed for the oxygenation reaction of olefin catalyzed by the complexes. In the case of the cobalt(II) complex, a σ-bound intermediate may also contribute to the reaction.