Intramolecular Electron Exchange Induced Oxygenation of Aldimine Functions of N,N'-bis(pyridin-2-ylmethylene)naphthyl-1,5-diimine in Isomeric Diruthenium Frameworks.

The article describes stepwise oxygenation of the aldimine functions at the backbone of N,N'-bis(pyridin-2-ylmethylene)naphthyl-1,5-diimine (L) in non-interconvertible L-bridged isomeric diruthenium(II)-acac complexes [{RuII(acac)2}2(µ-L)] (cis-1a/trans-1b, acac=acetylacetonate, DFT calculated DEcis-trans = 440 cm-1) via dioxygen activation.. It leads to the formation of the corresponding carboxamido bridged [{RuIII(acac)2}2(µ-Ld2-)] (cis-1ad/ trans-1bd; d denotes doubly-oxygenation) with the concomitant metal oxidation. However, L in doubly oxidized (RuIIIRuIII) congeners i.e. [{RuIII(acac)2}2(µ-L)](ClO4)2 (cis-[1a](ClO4)2/trans-[1b](ClO4)2) as well as electron poor metal fragments derived [{RuII(bpy)2}2(µ-L)]4+ [2](ClO4)4 (bpy=2,2'-bipyridine) and [{RuII(PPh3)2(CO)(H)}2(µ-L)]2+ [3](ClO4)2  failed to undergo the aforestated oxygenation process on purging O2 even at elevated temperature due to the absence of necessary electron exchange between ruthenium and L (i.e. RuII-L-RuII«RuIII-L·--RuII) to initiate the oxygen activation step. Besides structural and spectroscopic characterization of the complexes, oxygenation processes were further monitored through electrochemical, EPR and kinetic experiments in conjunction with DFT calculations, which highlighted mechanistic insights into the reaction sequence.