Metal-ligand synergy driven functionalisation of alkylene linked bis(aldimine) on a diruthenium(II) platform. Cyclisation oxygenation.

This article addresses the impact of metal-ligand redox cooperativity on the functionalisation of coordinated ligands. It demonstrates the structure-reactivity correlation of bis(aldimine) derived bis-bidentate L (Py-CHN-(CH)-NCH-Py, with = 2 (L1), 3 (L2), 4 (L3)) as a function of the conformation (/) of its alkylene linker as well as the overall structural form (/) of (acac)Ru(μ-L)Ru(acac) complex moieties (1-5) possessing an electron-rich acetylacetonate (acac) co-ligand. A systematic variation of the bridging alkylene unit of L in Ru/Ru-derived 1-5 led to the following reactivity/redox events, which were validated through structural, spectroscopic, electrochemical and theoretical evaluations: (i) Cyclisation of the ethylene linked ( conformation) bis-aldimine unit of L1 C-C coupling yielded pyrazine bridged (acac)Ru(μ-L1')Ru(acac), 1a, while the corresponding -form (ethylene linker) of the metal-bound L1 in 2 ((acac)Ru(μ-L1)Ru(acac)) led to oxygenation at the ligand backbone (bis-aldimine (L) → bis(carboxamido) (L'')) O activation to generate RuRu-derived (acac)Ru(μ-L1'')Ru(acac) (2a). (ii) Consequently, propylene and butylene linked L2 and L3 bridged between two {Ru(acac)} units in 3 and 4/5 underwent oxygenation of L to L'' to yield diruthenium(III) complexes 3a and 4a/5a, respectively. (iii) In contrast, analogous L bridged oxidised [(acac)Ru(μ-L)Ru(acac)](ClO) ([2](ClO)-[5](ClO)) and [{(PPh)(CO)(H)Ru}(μ-L)](ClO) ([6](ClO)-[8](ClO)) involving electron poor co-ligands failed to undergo the oxygenation of L irrespective of its value, reemphasising the effective role of redox interplay between Ru and L particularly in the presence of an electron-rich acac co-ligand in the functionalisation of the latter in 1a-5a.