Structural, electronic, and thermochemical preference for multi-PCET reactivity of ruthenium(II)-amine and ruthenium(IV)-amido complexes

Abstract

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 [RuII(bpy)(en*)2]2+ (RuII-H0 ) and [RuIV(bpy)(en*-H2)2]2+ (RuIV-H2 ) 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 favouring 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.