Insertion of Molecular Oxygen into Palladium and Platinum-sp3 Carbon Bonds

摘要

Synthesis of methanol from methane and terminal alcohols from linear alkanes using molecular oxygen as an oxidant under mild conditions is an attractive and environmentally-friendly transformation reaction. Insertion of molecular oxygen into a transition metal-carbon (sp~(3)) bond is a key step to achieve the transition metal complex-catalyzed transformation. In this review, two mechanistically-different insertion reactions of oxygen into palladium and platinum-carbon (sp~(3)) bonds are introduced. The former insertion is proposed to proceed by a radical chain mechanism, which is similar to that for the auto oxidation of organic compounds. A palladium(III) 17e~(-) intermediate, (bipy = 2,2'-bipyridine), which would be formed by the attack of a methylperoxy radical to , is regarded as a characteristic species in the proposed mechanism. On the other hand, the latter insertion involves loosely aggregated Pd(II) or Pt(II) methyl complexes, (L = 6,6''-diamino-2,2':6',2''-terpyridine), which would be excited to triplet complexes, ~(3)*, upon exposure to light. Subsequent coordination of triplet oxygen and further conversions including reductive elimination of a carbon (sp~(3))- oxygen bond at the final step afford .