A Non-Heme Diiron Complex for (Electro)catalytic Reduction of Dioxygen: Tuning the Selectivity through Electron Delivery

In
the oxygen reduction reaction (ORR) domain, the investigation
of new homogeneous catalysts is a crucial step toward the full comprehension
of the key structural and/or electronic factors that control catalytic
efficiency and selectivity. Herein, we report a unique non-heme diiron
complex that can act as a homogeneous ORR catalyst in acetonitrile
solution. This iron­(II) thiolate dinuclear complex, [FeII2(LS)­(LSH)] ([Fe2SH]+) (LS2– = 2,2′-(2,2′-bipyridine-6,6′-diyl)­bis­(1,1-diphenylethanethiolate))
contains a thiol group in the metal coordination sphere. [Fe2SH]+ is an efficient ORR catalyst both in the
presence of a one-electron reducing agent and under electrochemically
assisted conditions. However, its selectivity is dependent on the
electron delivery pathway; in particular, the process is selective
for H2O2 production under chemical conditions
(up to ∼95%), whereas H2O is the main product during
electrocatalysis (less than ∼10% H2O2). Based on computational work alongside the experimental data, a
mechanistic proposal is discussed that rationalizes the selective
and tunable reduction of dioxygen.