Reverse reactivity in hydroxylation of adamantane and epoxidation of cyclohexene catalyzed by the mononuclear ruthenium-oxo complexes with 6-substituted tripodal polypyridine ligands

The electronic character of the ruthenium complexes with tripodal polypyridine ligands, which is controlled by the substituted groups at pyridine 6-position, gives rise to differences in the reactivity for the ruthenium catalyzed hydroxylation of adamantane and epoxidation of cyclohexene with PhIO as an oxidant; Ru complexes containing electron-withdrawing groups (1, 3, and 5) promote the epoxidation, while those containing electron-donating groups (2, 4, and 6) promote the hydroxylation.