A Mononuclear Non-Heme Manganese(IV)–Oxo Complex Binding Redox-Inactive Metal Ions

Redox-inactive metal ions play pivotal roles in regulating
the
reactivities of high-valent metal–oxo species in a variety
of enzymatic and chemical reactions. A mononuclear non-heme Mn­(IV)–oxo
complex bearing a pentadentate N5 ligand has been synthesized
and used in the synthesis of a Mn­(IV)–oxo complex binding scandium
ions. The Mn­(IV)–oxo complexes were characterized with various
spectroscopic methods. The reactivities of the Mn­(IV)–oxo complex
are markedly influenced by binding of Sc3+ ions in oxidation
reactions, such as a ∼2200-fold increase in the rate of oxidation
of thioanisole (i.e., oxygen atom transfer) but a ∼180-fold
decrease in the rate of C–H bond activation of 1,4-cyclohexadiene
(i.e., hydrogen atom transfer). The present results provide the first
example of a non-heme Mn­(IV)–oxo complex binding redox-inactive
metal ions that shows a contrasting effect of the redox-inactive metal
ions on the reactivities of metal–oxo species in the oxygen
atom transfer and hydrogen atom transfer reactions.