Oxygen reduction reactivity of cobalt(II) hangman porphyrins

Cobalt(II) hangman porphyrins are delivered from easily available starting materials, in two steps, in good yields, and with abbreviated reaction times. Selected compounds from a library of Co(II) hangman porphyrins immobilized on multiwall carbon nanotubes establish that the four-electron four-proton catalytic reduction of oxygen to water in aqueous solution can be achieved at the single cobalt center of the hangman platform. Reaction trends within the library reveal that the selective reduction of O(2) to H(2)O occurs at electron deficient hangman porphyrin platforms possessing a distal group that is capable of proton transfer.