Hydroxopalladium(iv) complexes prepared using oxygen or hydrogen peroxide as oxidants

Abstract

The cycloneophylpalladium(II) complexes [Pd(CH₂CMe₂C₆H₄)(κ²-N,N′-L)], 1 or 2, with L = RO(CH₂)₃N(CH₂-2-C₅H₄N)₂, with R = H or Me, respectively, react with either dioxygen or hydrogen peroxide in the presence of NH₄[PF₆] to give rare examples of the corresponding hydroxopalladium(IV) complexes [Pd(OH)(CH₂CMe₂C₆H₄)(κ³-N,N′,N′′-L)][PF₆], 3 or 4. The complexes 3 and 4 are stable at room temperature and have been structurally characterized. On heating a solution of 3 or 4 in moist dimethylsulphoxide, selective reductive elimination with C(sp²)–O bond formation is observed, followed by hydrolysis, to give the corresponding pincer complex [Pd(OH)(κ³-N,N′,N′′-L)][PF₆] and 2-t-butylphenol as major products. A more complex reaction occurs in chloroform solution. The mechanisms of reaction are discussed, supported by DFT calculations.