Diverse Coordination Modes and Bidirectional Noninnocence of Pyridyl-ß-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) (κ2-[O,O]-, κ2-[N,O]-, and µ-bis-κ2-[N,O]-) on selective ruthenium platforms: Ru(acac)2 (dimeric [1]ClO4), Ru(bpy)2 (monomeric [2]ClO4), Ru(pap)2 (isomeric monomeric [3]ClO4/[4]ClO4, dimeric [5](ClO4)3), and Ru(PPh3)2(CO) (monomeric 6, isomeric dimeric [7]ClO4/[8]ClO4) (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]ClO4, (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 ß-diketiminate was reported to activate O2 on the selective Ru(acac)2 platform, the inability of analogous ß-diketonate-derived [1]ClO4 could be attributed to its calculated greater HOMO-LUMO energy gap, which disfavored electron exchange at the metal(RuIII)-ligand(L-) interface to introduce the required unpaired spin at the ligand backbone toward the 3O2 activation event.

Metal-ligand synergy driven functionalisation of alkylene linked bis(aldimine) on a diruthenium(II) platform. Cyclisation versus 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-(CH2)n-NCH-Py, with n = 2 (L1), 3 (L2), 4 (L3)) as a function of the conformation (syn/anti) of its alkylene linker as well as the overall structural form (cis/trans) of (acac)2RuII(µ-L)RuII(acac)2 complex moieties (1-5) possessing an electron-rich acetylacetonate (acac) co-ligand. A systematic variation of the bridging alkylene unit of L in RuII/RuII-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 (syn conformation) bis-aldimine unit of L1 via C-C coupling yielded pyrazine bridged (acac)2RuII(µ-L1')RuII(acac)2, 1a, while the corresponding anti-form (ethylene linker) of the metal-bound L1 in 2 ((acac)2RuII(µ-L1)RuII(acac)2) led to oxygenation at the ligand backbone (bis-aldimine (L) → bis(carboxamido) (L'')) via O2 activation to generate RuIIIRuIII-derived (acac)2RuIII(µ-L1''2-)RuIII(acac)2 (2a). (ii) Consequently, propylene and butylene linked L2 and L3 bridged between two {Ru(acac)2} 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)2RuIII(µ-L)RuIII(acac)2](ClO4)2 ([2](ClO4)2-[5](ClO4)2) and [{(PPh3)2(CO)(H)RuII}2(µ-L)](ClO4)2 ([6](ClO4)2-[8](ClO4)2) involving electron poor co-ligands failed to undergo the oxygenation of L irrespective of its n value, reemphasising the effective role of redox interplay between RuII and L particularly in the presence of an electron-rich acac co-ligand in the functionalisation of the latter in 1a-5a.

Dioxygen Activation by Redox-Active Bis(aldimine) Ligand Bridged Diruthenium Complex Possessing Singlet Ground State.

The unexplored 'actor' behavior of redox-active bis(aldimine) congener, p-phenylene-bis(picoline)aldimine (L1), towards dioxygen activation and subsequent functionalization of its backbone was demonstrated on coordination with {Ru(acac)2 } (acac= acetylacetonate). Reaction under aerobic condition led to the one-pot generation of dinuclear complexes with unperturbed L1, imino-carboxamido (L2- ), and bis(carboxamido) (L32- )-bridged isovalent {RuII (µ-L1)RuII }, 1/ {RuIII (µ-L32- )RuIII }, 3 and mixed-valent {RuII (µ-L2- )RuIII }, 2. Authentication of the complexes along with the redox non-innocence behavior of their bridge have been validated through structure, spectroelectrochemistry and DFT calculations. Kinetic and isotope labelling experiments together with DFT analyzed transition states justified the consideration of redox shuttling at metal/L1 interface for 3 O2 activation despite of the closed shell configuration of 1 (S=0) to give carboxamido derived 2/3.

Redox-Induced Intramolecular C-C Coupling of Acyclic Bis(2-pyridylmethylene)ethylenediamine on a Ru(acac)2 Platform.

The paper documents redox-triggered C-C coupling of acyclic N,N'-bis(2-pyridylmethylene)ethylenediamine (BPE) to yield 2,3-bis(2-pyridyl)pyrazine (DPP) upon coordination to an electron-rich {Ru(acac)2} (acac = acetylacetonate) unit. This led to DPP-bridged [{Ru(acac)2}2(DPP)]0/+ (2 and [2]ClO4) along with the unperturbed BPE-bridged [{Ru(acac)2}2(BPE)] (1). On the contrary, electron-poor {Ru(Cl)(H)(CO)(PPh3)3} yielded BPE-bridged [3](ClO4)2 as an exclusive product. Synergistic metal (Ru)-ligand (BPE) redox participation toward chemical noninnocence of the Schiff base ligand and DPP-mediated electronic communication in RuIIRuIII-derived [2]ClO4 are addressed.