Water-soluble Fe(II)-H2O complex with a weak O-H bond transfers a hydrogen atom via an observable monomeric Fe(III)-OH.

Understanding the metal ion properties that favor O–H bond formation versus cleavage should facilitate the development of catalysts tailored to promote a specific reaction, e.g., C–H activation or H2O oxidation. The first step in H2O oxidation involves the endothermic cleavage of a strong O–H bond (BDFE = 122.7 kcal/mol), promoted by binding the H2O to a metal ion, and by coupling electron transfer to proton transfer (PCET). This study focuses on details regarding how a metal ion’s electronic structure and ligand environment can tune the energetics of M(HO–H) bond cleavage. The synthesis and characterization of an Fe(II)–H2O complex, 1, that undergoes PCET in H2O to afford a rare example of a monomeric Fe(III)–OH, 7, is described. High-spin 7 is also reproducibly generated via the addition of H2O to {[FeIII(OMe2N4(tren))]2-(μ-O)}2+ (8). The O–H bond BDFE of Fe(II)–H2O (1) (68.6 kcal/mol) is calculated using linear fits to its Pourbaix diagram and shown to be 54.1 kcal/mol less than that of H2O and 10.9 kc...