Structural, Electronic, and Thermochemical Preference for Multi-PCET Reactivity of Ruthenium(II)-Amine and Ruthenium(IV)-Amido Complexes

The multiredox reactivity of bioinorganic cofactors is often coupled to proton transfers. Here we investigate the structural, thermochemical, and electronic structure of ruthenium-amino/amido complexes with multi- proton-coupled electron transfer reactivity. The bis(amino)ruthenium(II) and bis(amido)ruthenium(IV) complexes [Ru-II(bpy)(en*)(2)](2+) (Ru-II-H-0) and [Ru-IV(bpy)(en*-H-2)(2)](2+) (Ru-IV-H-2) interconvert reversibly with the transfer of 2e(-)/2H(+) (bpy=2,2'-bipyridine, en*=2,3-diamino-2,3-dimethylbutane). X-ray structures allow correlations between the structural and electronic parameters, and the thermochemical data of the 2e(-)/2H(+) multi-square grid scheme. Redox potentials, acidity constants and DFT calculations reveal potential intermediates implicated in 2e(-)/2H(+) reactivity with organic reagents in non-protic solvents, which shows a strong inverted redox potential favoring 2e(-)/2H(+) transfer. This is suggested to be an attractive system for potential one-step (concerted) transfer of 2e(-)and 2H(+) due to the small changes of the pseudo-octahedral geometries and the absence of charge change, indicating a relatively small overall reorganization energy.

Automated summary

The study investigates the structural, thermochemical, and electronic structure of ruthenium-amino/amido complexes with multi-proton-coupled electron transfer reactivity. Through experimental and computational analysis, redox potentials, acidity constants, and DFT calculations are used to reveal potential intermediates involved in the 2e(-)/2H(+) reactivity with organic reagents in non-protic solvents. The findings suggest that this system may be attractive for potential one-step transfer of 2e(-) and 2H(+) due to small changes in geometry and absence of charge change, indicating relatively low overall reorganization energy.