Redox Potentials of High‐Valent Iron‐, Cobalt‐, and Nickel‐Oxido Complexes: Evidence for Exchange Enhanced Reactivity. Issue 10 (25th May 2020)

• Record Type: Journal Article
• Authors: Comba, Peter; Löhr, Anna‐Maria; Pfaff, Florian; Ray, Kallol
• Is Part Of: Israel journal of chemistry. Volume 60:Issue 10/11(2020)
• Page Start: 957
• Page End: 962
• Publication Date: 2020-05-25
• Subjects: exchange enhanced reactivity -- high-valent metal-oxido complexes -- reduction potential -- non heme iron -- late transition metals; Chemistry -- Periodicals; 540.5
• DOI: 10.1002/ijch.202000038
• Languages: English
• ISSNs: 0021-2148

Abstract

Abstract: The ferrocene titration method has been employed to determine the one‐electron reduction potentials of a series of oxido‐iron(IV), oxido‐cobalt(IV) and oxido/hydroxido‐nickel(III) complexes based on the same tetradentate TMG3 tren ligand (TMG3 tren=tris[2‐( N ‐tetramethylguanidyl)ethyl]amine). The S =2 ground state of the [(TMG3 tren)Fe IV =O] 2+ complex allows an exchange enhanced reactivity, which enables it to perform efficient oxygen atom transfer (OAT) and hydrogen atom abstraction (HAA) reactions with a low one‐electron reduction potential of 270 mV vs . SCE. In the absence of exchange enhanced reactivity, the OAT and HAA abilities of the S =3/2 [(TMG3 tren)Co IV −O(Sc(OTf)3 )] 2+, S =1/2 [(TMG3 tren)Ni III −O(H)] 2+ and the previously reported S =1 [(TMC)(CH3 CN)Fe IV =O] 2+ and [(N4Py)Fe IV =O] 2+ complexes can be directly correlated to their reduction potentials. Notably, [(N4Py)Fe IV =O] 2+ and [(TMG3 tren)Fe IV =O] 2+ exhibit similar OAT and HAA reactivities although the reduction potential of [(N4Py)Fe IV =O] 2+ is 0.24 V more positive than that of [(TMG3 tren)Fe IV =O] 2+ . The present study therefore provides experimental evidence for exchange enhanced reactivity and rationalizes nature's choice for employing S =2 oxido‐iron(IV) cores to achieve difficult oxidation reactions at biologically viable potentials. Abstract :