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 (ρ=−0.58) and electron‐withdrawing groups on the 4,4′‐disubstituted‐2,2′‐bipyridine ligand (ρ=+0.18) increase the reaction rate. The results indicate partial reduction of the palladium centre in the transition state of the rate‐limiting step.