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 2 -[O,O] - , κ 2 -[N,O] - , and μ-bis-κ 2 -[N,O] - ) on selective ruthenium platforms: Ru(acac) 2 (dimeric [ 1 ]ClO 4 ), Ru(bpy) 2 (monomeric [ 2 ]ClO 4 ), Ru(pap) 2 (isomeric monomeric [ 3 ]ClO 4 /[ 4 ]ClO 4 , dimeric [ 5 ](ClO 4 ) 3 ), and Ru(PPh 3 ) 2 (CO) (monomeric 6 , isomeric dimeric [ 7 ]ClO 4 /[ 8 ]ClO 4 ) (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 [ 8 ]ClO 4 , (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 2 on the selective Ru(acac) 2 platform, the inability of analogous β-diketonate-derived [ 1 ]ClO 4 could be attributed to its calculated greater HOMO-LUMO energy gap, which disfavored electron exchange at the metal(Ru III )-ligand(L - ) interface to introduce the required unpaired spin at the ligand backbone toward the 3 O 2 activation event.