Energy Landscape for the Electrocatalytic Oxidation of Water by a Single-Site Oxomanganese(V) Porphyrin.

A cationic manganese porphyrin, Mn III -TDMImP, is an efficient, homogeneous, single-site water oxidation electrocatalyst at neutral pH. The measured turnover frequency for oxygen production is 32 s -1 . Mechanistic analyses indicate that Mn V (O)(OH 2 ), the protonated form of the corresponding trans -Mn V (O) 2 species, is generated from the Mn III (OH 2 ) 2 precursor in a 2-e - two-proton process and is responsible for O-O bond formation with a H 2 O molecule. Chloride ion is a competitive substrate with H 2 O for the Mn V (O)(OH 2 ) oxidant, forming hypochlorous acid with a rate constant that is 3 orders of magnitude larger than that of water oxidation. The data allow the construction of an experimental energy landscape for this water oxidation catalysis process.