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

The cycloneophylpalladium(II) complexes [Pd(CH 2 CMe 2 C 6 H 4 )(κ 2 - N,N '-L)], 1 or 2, with L = RO(CH 2 ) 3 N(CH 2 -2-C 5 H 4 N) 2 , with R = H or Me, respectively, react with either dioxygen or hydrogen peroxide in the presence of NH 4 [PF 6 ] to give rare examples of the corresponding hydroxopalladium(IV) complexes [Pd(OH)(CH 2 CMe 2 C 6 H 4 )(κ 3 - N,N ' ,N ''-L)][PF 6 ], 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(sp 2 )-O bond formation is observed, followed by hydrolysis, to give the corresponding pincer complex [Pd(OH)(κ 3 - N,N ' ,N ''-L)][PF 6 ] 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.