Catalytic conversions in water. Part 22: Electronic effects in the (diimine)palladium(II)-catalysed aerobic oxidation of alcohols

The electronic effects in the (diimine)Pd(II)-catalysed aerobic oxidation of alcohols were investigated from the viewpoint of both the catalyst and the alcohol. A 'push-pull' mechanism is operative, where both electron-donating substituents on the benzyl alcohol (p = - 0.58) and electron-withdrawing groups on the 4,4'-disubstituted-2,2'-bipyridine ligand (p = + 0.18) increase the reaction rate. The results indicate partial reduction of the palladium centre in the transition state of the rate-limiting step.