Oxygen Reduction with a Bifunctional Iridium Dihydride Complex

The iridium dihydride [Ir(H) 2 ( H PNP)] + (PNP=N(CH 2 CH 2 P t Bu 2 ) 2 ) reacts with O 2 to give the unusual, square‐planar iridium(III) hydroxide [Ir(OH)(PNP)] + and water. Regeneration of the dihydride with H 2 closes a quasi‐catalytic synthetic oxygen‐reduction reaction (ORR) cycle that can be run several times. Experimental and computational examinations are in agreement with an oxygenation mechanism via rate‐limiting O 2 coordination followed by H‐transfer at a single metal site, facilitated by the cooperating pincer ligand. Hence, the four electrons required for the ORR are stored within the two covalent MH bonds of a mononuclear metal complex.