Applications of the Marcus cross relation to inner sphere reduction of O2: implications in small-molecule activation†
Application of the Marcus cross relation (MCR) to determine electron transfer rate constants is well documented. In addition to outer sphere reduction/oxidation of O2/O2˙−, the MCR is also applicable for proton transfer (PT), proton-coupled electron transfer (PCET), and hydride transfer rate constants. A question this report aims to address is whether or not the MCR can predict rate constants for inner sphere electron transfer (ISET) reactions between iron complexes and O2. By including the iron–superoxide bond dissociation energy (BDFEFe–O2) into the MCR equilibrium constant, close values to experimental inner sphere O2 reductions are estimated. This insight of including the iron–superoxide binding energy as a design element for the development of synthetic oxygenases is considered.