Diverse Coordination Modes and Bidirectional Noninnocence of Pyridyl-β-diketonate on Ruthenium Platforms as a Function of Coligands.

The article demonstrated diverse binding modes of deprotonated 1,3-di(2-pyridinyl)-1,3-propanedione (HL) (κ-[O,O], κ-[N,O], and μ-bis-κ-[N,O]) on selective ruthenium platforms: Ru(acac) (dimeric []ClO), Ru(bpy) (monomeric []ClO), Ru(pap) (isomeric monomeric []ClO/[]ClO, dimeric [](ClO)), and Ru(PPh)(CO) (monomeric , isomeric dimeric []ClO/[]ClO) (acac = acetylacetonate, bpy = 2,2-bipyridine, pap = 2-phenylazopyridine). Structural authentication of the complexes revealed (i) diverse binding mode of L including its unprecedented bridging mode in []ClO, (ii) varying degrees of nonplanarity of L, and (iii) development of 1D polymeric chains or dimeric/tetrameric forms via intermolecular π-π interactions. The preferential binding feature of L in the complexes could also be corroborated by their calculated relative energies. The analysis of the multiredox steps of the complexes suggested severe mixing of metal-ligand frontier orbitals, which in effect pinpointed the involvement of L in both the oxidative and reductive processes along the redox chain, suggesting its bidirectional noninnocence under the present coordination situations. Though α-diketone or β-diketiminate was reported to activate O on the selective Ru(acac) platform, the inability of analogous β-diketonate-derived []ClO could be attributed to its calculated greater HOMO-LUMO energy gap, which disfavored electron exchange at the metal(Ru)-ligand(L) interface to introduce the required unpaired spin at the ligand backbone toward the O activation event.