Fine Tuning between Radical versus Nonradical States of Azoheteroarenes on Selective Osmium Platforms.

The article highlights the cooperative impact of azoheteroarenes [abbt: 2,2'-azobis(benzothiazole), L1-L3; bmpd: ()-1,2-bis(1-methyl-1-pyrazole-3-yl) diazene, L4] and coligands [bpy: 2,2'-bipyridine; pap: 2-phenylazopyridine] in tuning radical (N-N) versus nonradical (N═N) states of L on selective Os-platforms in structurally/spectroscopically characterized monomeric []ClO-[]ClO and [](ClO)-[](ClO)/[](ClO)-[](ClO), respectively. The preferred -configuration of L in the complexes prevented obtaining ligand bridged dimeric species. It revealed that {Os(bpy)} facilitated the stabilization of both nonradical ([](ClO)-[](ClO)) and radical ([]ClO-[]ClO) states of L1/L2, while it delivered exclusively the radical form for L3 in []ClO.

Sequential Oxygenation of Bis(β-diketiminate) on a Selective Diruthenium Platform.

This article demonstrated the redox-noninnocent phenylene-linked bis(β-diketiminate) (L)-bridged first example of isomeric diruthenium(III)-acac species (acac = acetylacetonate) and its ability to activate dioxygen. The coordination of deprotonated L to the {Ru(acac)} in bis(bidentate) mode led to isomeric {(acac)Ru}(μ-L) ( = 1, -/- ). displayed Ru(III)-based anisotropic EPR in CHCN but without the resolution of the forbidden (Δ = 2) signal at 77 K.

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).

The isomer-sensitive electrochemical HER of ruthenium(II)-hydrido complexes involving redox-active azoheteroaromatics.

The article deals with the development of isomeric ruthenium(II)-hydrido complexes [Ru(H)(L1)(PPh)(CO)]ClO ([1a]ClO-[1b]ClO)/[Ru(H)(L2)(PPh)(CO)]ClO ([2a]ClO-[2b]ClO) involving azo coupled L1 [L1: ()-1,2-bis(1-methyl-1-pyrazol-3-yl)diazene]/L2 [L2: ()-1,2-bis(4-iodo-1-methyl-1-pyrazol-3-yl)diazene], respectively. Structural evaluation of the complexes affirmed the conformation of the coordinated/uncoordinated pyrazole groups of L and its unperturbed neutral azo (NN) state. Isomeric forms in [1a]ClO/[1b]ClO or [2a]ClO/[2b]ClO differed with respect to the and orientations of the coordinated CO and N(azo) donor of L, respectively.

Donor-acceptor bridge 2,5-bis(2-oxido-phenyl)thiazolo-[5,4-]thiazole derived diruthenium and diosmium systems. Structural and competitive electronic events as a function of metal ion, bridge and ancillary ligand.

The article deals with the structural and electronic forms of hitherto unexplored L (HL = 2,5-bis(2-hydroxyphenyl)thiazolo-[5,4-]thiazole) bridged analogous diruthenium [{(AL1/AL2) Ru}(μ-L)] [1](ClO)/[2](ClO) and diosmium [{(AL1/AL2)Os}(μ-L)] [3](PF)/[4](ClO) complexes as a function of moderate-to-strongly π-accepting ancillary ligands: AL1 = 2,2'-bipyridine (bpy) and AL2 = 2-phenylazopyridine (pap). Structural elucidation of the complexes established an -oriented bridge (L) linked to the metal units through its N,O/O,N-donor sets, which led to two six-membered chelates in each case. It also highlighted the twisting of the phenolato functions of L with respect to the central thiazolothiazole (TzTz) unit and the unreduced state of the azo function of AL2 and multiple non-covalent π⋯π/CH⋯π interactions within the molecules in the nearby asymmetric units.

Inner-Sphere Electron Transfer Induced Reversible Electron Reservoir Feature of Azoheteroarene Bridged Diruthenium Frameworks.

This article demonstrates the stabilization of ground- and redox-induced metal-to-ligand charge transfer excited states on coordination of azo-coupled bmpd(L4) [bmpd = ()-1,2-bis(1-methyl-1-pyrazol-3-yl)diazene; L4 = -N═N-] to the electron-rich {Ru(acac)} (acac = acetylacetonate) unit in mononuclear Ru(acac)(L4) () and diastereomeric dinuclear (acac)Ru(μ-L4)Ru(acac) [, ΔΔ/ΛΛ ()/, ΔΛ ()] complexes, respectively. It also develops further one-step intramolecular electron transfer induced L4 bridged isovalent higher analogue [(acac)Ru(μ-L4)Ru(acac)]ClO in diastereomeric forms, -[]ClO-[]ClO. On the contrary, under identical reaction conditions electronically and sterically permuted bimpd [L5, ()-1,2-bis(4-iodo-1-methyl-1-pyrazol-3-yl)diazene)] delivered mononuclear Ru(acac)(L5) () as an exclusive product.

On the Question of S-S Bond Cleavage of 2,2'-Dithiodipyridine on Selective Ru and Os Platforms. MLCT or Hydride or Solvent Mediated Event.

This article deals with the S-S bond scission of the model substrate 2,2'-dithiodipyridine (DTDP) in the presence of a selective set of metal precursors: Ru(acac), [RuCl(PPh)], [RuHCl(CO)(PPh)], [Ru(H)(CO)(PPh)], [Ru(bpy)Cl], [Ru(pap)Cl], [Os(bpy)Cl], and [Os(pap)Cl] (acac, acetylacetonate; bpy, 2,2'-bipyridine; pap, 2-phenylazopyridine). This led to the eventual formation of the corresponding mononuclear complexes containing the cleaved pyridine-2-thiolate unit in -/[]ClO-[]ClO. The formation of the complexes was ascertained by their single-crystal X-ray structures, which also established sterically constrained four-membered chelate (average N1-M-S1 angle of 67.

Diosmium compounds containing bis(imidazole)--quinone bridging ligands.

The doubly deprotonated bridging ligand L derived from 2,6-bis(2-pyridyl)-1,5-dihydro-1',4'-benzoquinono[2',3'-:5',6'-']diimidazole HL forms coordination compounds with two bis(2,2'-bipyridine)osmium(II) complex fragments in ([1](ClO)) and configurations ([2](ClO)) of {(μ-L)[Os(bpy)]}(ClO), as evident from crystal structure analyses. Exchange of the metal-coordinating 2-pyridyl functions in the bridge through non-coordinating 4-tolyl substituents (L → L) leads to [3](ClO) which involves chelation of the [Os(bpy)] groups through imidazole-N and carbonyl-O atoms of the central -quinone function. In addition to identification, the compounds were subjected to electrochemical (CV, DPV) and spectroelectrochemical (UV-vis-NIR, EPR) analyses of electron transfer, the results being supported by results from TD-DFT calculations.

Redox induced oxidative C-C coupling of non-innocent bis(heterocyclo)methanides.

Redox driven C-C bond formation has gained recent attention over the traditional sequence of oxidative addition, insertion and reductive elimination reactions. In this regard, the transient radical mediated diverse reactivity profile of bis(heterocyclo)methanes (H-BHM: HL1-HL4) has been demonstrated as a function of varying metal ions and ligand backbones. It highlighted the following events: (a) redox induced homocoupling of deprotonated HL1 and HL4 on coordination to M(OAc) precursors (M = Cu, Zn, Pd, Ag), including the effective role of molecular oxygen in the transformation process; (b) steric inhibition of C-C coupling of HL1 or HL4 on inserting the substituent at the bridged methylene centre (Ph in HL2 or CH in HL3); (c) competitive C-C coupling oxygenation of free HL1 with varying concentrations of Pd(OAc) as the ease of oxygenation over dimerisation of the deprotonated HL1 was corroborated by the DFT calculated lower activation barrier and greater thermodynamic stability of the former; and (d) redox non-innocence of BHMs on a coordinatively inert ruthenium platform, which in turn favored the involvement of a radical pathway for the aforestated coupling or oxygenation process.

Redox induced S-S bond cleavage of 2,2'-dithiobisbenzothiazole - leading to a [2Ru-2S] core analogous to [2Fe-2S] cluster.

Facile reduction of 2,2'-dithiobisbenzothiazole by the mediation of metal-to-ligand charge transfer or by internal reducing equivalent is demonstrated. It leads to various binding modes of thiolates (κ, κ, μ) in a series of mononuclear and dinuclear ruthenium complexes. The dinuclear complex exhibited electron transfer processes similar to a [2Fe-2S] cluster.

Host-Guest Feature of DPPP Bridged Arene-Ruthenium Clip Derived Molecular Rectangle.

The development of DPPP (HDPPP = 2,5-dihydro-3,6-di-2-pyridylpyrrolo(3,4-)pyrrole-1,4-dione) bridged () diruthenium complexes [(Cym)(X)Ru(μ-dppp)Ru(X)(Cym)] (Cym = -cymene and X = OTf (), SCN (), N (), NO()) are considered as the probable molecular clips for the construction of metallarectangle. Crystal structures of - established anticonfiguration with respect to monodentate SCN, N and NO groups, respectively. Though molecular clips - failed to provide the desired metallarectangle in combination with the 4,4'-bipyridine spacer, with the labile OTf groups facilitated to achieve the metallarectangle .