Ruthenium, Rhodium, Osmium, and Iridium Complexes of Osazones (Osazones = Bis-Arylhydrazones of Glyoxal): Radical versus Nonradical States

Mixed-valence di-ruthenium(II,III) complexes of redox non-innocent N-aryl-o-phenylenediamine derivatives

A mononuclear ruthenium(ii), [(L1IQ)Ru2+(PPh3)2Cl2]·CHCl3 (1·CHCl3), a di-ruthenium(ii,ii), [(L2IQ)2Ru24+Cl4(PPh3)2] (2) and a mixed-valence di-ruthenium(ii,iii), [(L3IQ)Ru25+Cl5(PPh3)2]·MeOH (3·MeOH) complex, where L1IQ, L2IQ and L3IQ are, respectively, o-diiminobenzoquinone forms of redox non-innocent N-(5-nitropyridyl)-o-phenylenediamine (L1H2), N-(2,4-dinitrophenyl)-o-phenylenediamine (L2H2) and N-(3-nitropyridyl)-o-phenylenediamine (L3H2) derivatives, were successfully isolated. The molecular and electronic structures of 1·CHCl3, 2 and 3·MeOH were confirmed by single-crystal X-ray crystallography, EPR, UV-Vis-NIR spectroscopies and density functional theory (DFT) calculations. Both 1·CHCl3 and 2 exhibited reversible anodic waves due to the Ru(iii)/Ru(ii) redox couple, while the cyclic voltammogram of 3·MeOH displayed two successive cathodic waves due to ruthenium(iii)/ruthenium(ii) and (L3IQ/L3ISQ) redox couples. EPR spectroscopy and DFT calculations inferred that 1+ is a ruthenium(iii) complex of L1IQ, [(L1IQ)Ru3+(PPh3)2Cl2]+, 2+ is a mixed-valence di-ruthenium(ii,iii) complex of L2IQ, [(L2IQ)2Ru25+Cl4(PPh3)2]+ and 3- is a di-ruthenium(ii,ii) complex, [(L3IQ)Ru24+Cl5(PPh3)2]-, while 32- is a di-ruthenium(ii,ii) complex of L3ISQ, [(L3ISQ)Ru24+Cl5(PPh3)2]2-, where L3ISQ is the o-diiminobenzosemiquinonate anion radical form of the L3H2 with a significant contribution of the mixed-valence di-ruthenium(iii,ii) form, [(L3AM)Ru25+Cl5(PPh3)2]2- (L3AM is the di-amido form of the L3H2 ligand). The spin density obtained from the Mulliken spin population analyses of the broken-symmetry (BS) DFT calculations was localized on Ru(2) in 3, while it was delocalized over both Ru(1) and the o-phenylenediamine fragment in 32-. The inter-valence charge-transfer (IVCT) transitions of 2+ and 3 were relatively weaker and occurred at 1680 and 1685 nm, respectively, while 32- exhibited a broader NIR absorption band at 1500-2000 nm. The calculated electronic-coupling parameters (Hab) using the Mulliken-Hush equation for 3 and 2+ ion, respectively, were 62 and 103 cm-1, defining these as Robin-Day class II mixed-valence systems.

Metal promoted conversion of aromatic amines to ortho-phenylenediimine derivatives by a radical coupling path

Transition metal promoted conversion of o-substituted arylamines to o-phenylenediimine derivatives by a radical C–N coupling path is reported.

Palladium(ii) and platinum(ii) complexes of glyoxalbis(N-aryl)osazone: molecular and electronic structures, anti-microbial activities and DNA-binding study

A new family of palladium(ii) and platinum(ii) complexes of redox non-innocent osazone ligands that exhibit moderate antileishmanial activity were isolated.

A Redox-Active Cascade Precursor: Isolation of a Zwitterionic Triphenylphosphonio-Hydrazyl Radical and an Indazolo-Indazole Derivative

A redox-active [ML] unit (M = Co^II and Mn^II; LH₂ = N'-(1,4-dioxo-1,4-dihydronaphthalen-2-yl)benzohydrazide) defined as a cascade precursor that undergoes a multicomponent redox reaction comprising of a C-N bond formation, tautomerization, oxidation, C-C coupling, demetalation, and affording 6,14-dibenzoylbenzo[f]benzo[5,6]indazolo[3a,3-c]indazole-5,8,13,16-tetraone (^IndL₂) is reported. Conversion of LH₂ → ^IndL₂ in air is overall a (6H⁺+6e) oxidation reaction, and it opens a route for the syntheses of bioactive diarylindazolo[3a,3-c]indazole derivatives. The reaction occurs via a radical coupling reaction, and the radical intermediate was isolated as a triphenylphosphonio adduct. In presence of PPh₃ the [ML] unit promotes a reaction that involves a C-P bond formation, tautomerization, and oxidation to yield a stable zwitterionic triphenylphosphonio-hydrazyl radical (^PPh3L^±•). Conversion of LH₂ → ^PPh3L^±• is a (3H⁺+3e) oxidation reaction. To authenticate the [ML] unit, in addition to the ^IndL₂, a zinc(II) complex, [(L₃)Zn^II(H₂O)Cl]·2MeOH (1·2MeOH), was successfully isolated (L₃H = a pyridazine derivative of 1,4 naphthoquinone) from a reaction of LH₂ with hydrated ZnCl₂. Conversion of 3LH₂ → 1 is also a multicomponent (6H⁺+6e) oxidation reaction promoted by zinc(II) ion via a radical intermediate. Facile oxidation of [L^2-] to [L^•-] that was considered as an intermediate of these conversions was confirmed by isolating a 1,4 naphthoquinone-benzhydrazyl radical (LH^•) complex, [(LH^•)Zn^II(H₂O)Cl₂] (2H^•). The intermediates of LH₂ → ^IndL₂, LH₂ → ^PPh3L^±•, and 3LH₂ → 1 conversions were analyzed by electrospray ionization mass spectroscopy. The molecular and electronic structures of ^PPh3L^±•, ^IndL₂, 1·2MeOH, and 2H^• were confirmed by single-crystal X-ray crystallography, electron paramagnetic resonance spectroscopy, and density functional theory calculations.

Coordination of o-benzosemiquinonate, o-iminobenzosemiquinonate and aldimine anion radicals to oxidovanadium(iv)

o-Benzosemiquinonate, o-iminobenzosemiquinonate and hitherto unknown aldimine anion radical complexes of oxidovanadium(iv) are reported.

Glyoxalbis(2-methylmercaptoanil) complexes of nickel and ruthenium: radical versus non-radical states

The molecular and electronic structures of nickel(ii) and ruthenium(ii) complexes of glyoxalbis(2-methylmercaptoanil) and their reduced and oxidized analogues are reported.

Arylamino radical complexes of ruthenium and osmium: dual radical counter in a molecule

Radical and non-radical ruthenium and osmium complexes of 1-amino-9,10-anthraquinone (AqNH₂), which is defined as a molecule of dual radical counter, are disclosed. 1-Amido-9,10-anthraquinone (AqNH^-) complexes of the types trans-[Ru^II(AqNH^-)(PPh₃)₂(CO)Cl] (1), trans-[Os^II(AqNH^-)(PPh₃)₂(CO)Br] (2) and trans-[Ru^III(AqNH^-)(PPh₃)₂Cl₂] (3) were isolated. AqNH^- of 1-3 is redox active and undergoes oxidation reversibly at +(0.05-0.35) V to the 1-amino-9,10-anthraquinone radical (AqNH˙) and reduction at -(0.86-1.60) V to the 1-amido-9,10-anthrasemiquinonate anion radical (Aq^NHSQ˙^2-). The reaction of 2 with I₂ in CH₂Cl₂ afforded a crystalline AqNH˙ complex of the type trans-[Os^II(AqNH˙)(PPh₃)₂(CO)Br]⁺I₅^-·½I₂ (2⁺I₅^-·½I₂). AqNH˙ and Aq^NHSQ˙^2- complexes of the types trans-[Ru^II(AqNH˙)(PPh₃)₂(CO)Cl]⁺ (1⁺), trans-[Ru^III(AqNH˙)(PPh₃)₂Cl₂]⁺ (3⁺), trans-[Ru^II(Aq^NHSQ˙^2-)(PPh₃)₂(CO)Cl]^- (1^-) and trans-[Os^II(Aq^NHSQ˙^2-)(PPh₃)₂(CO)Br]^- (2^-) were generated chemically/electrochemically in solution. The electronic states of the complexes were authenticated by single crystal X-ray structure determinations of 1, 2·5/4 toluene, 3 and 2⁺I₅^-·½I₂, EPR spectroscopy and density functional theory (DFT) calculations. AqNH˙ instigates a 2c-3e p_π-d_π interaction and the length in 2⁺I₅^-·½I₂, 1.978(5) Å, is relatively shorter than the Os^II-NH_Aq^- length, 2.037(2) Å, while the Aq-NH˙ bond, 1.365(8) Å, is longer than the Aq-NH^- bond, 1.328(3) Å. DFT calculations predicted that the atomic spin is delocalized over the ligand backbone (1⁺, 56%) particularly in one of the p-orbitals of the nitrogen and the metal atoms of the 1⁺ and 2⁺ ions, while the spin is dominantly localized on the anthraquinone fragment of the 1^- and 2^- ions. TD DFT calculations were employed to elucidate the origins of the lower energy absorption bands of the neutral complexes. Hypsochromic shifts of the UV-vis-NIR absorption maximum during 1→1⁺, 2→2⁺ and 3→3⁺ conversions were recorded by spectroelectrochemical measurements.

Tris(2,2'-azobispyridine) complexes of copper(II): X-ray structures, reactivities, and the radical nonradical bis(ligand) analogues

Tris(abpy) complexes of types mer-[Cu(II)(abpy)3][PF6]2 (mer-1(2+)[PF6(–)]2) and ctc-[Cu(II)(abpy)2(bpy)][PF6]2 (ctc-2(2+)[PF6(–)]2) were successfully isolated and characterized by spectra and single-crystal X-ray structure determinations (abpy = 2,2′-azobispyridine; bpy = 2,2′-bipyridine). Reactions of mer-1(2+) and ctc-2(2+) ions with catechol, o-aminophenol, p-phenylenediamine, and diphenylamine (Ph–NH–Ph) in 2:1 molar ratio afford [CuI(abpy)2](+) (3(+)) and corresponding quinone derivatives. The similar reactions of [Cu(II)(bpy)3](2+) and [Cu(II)(phen)3](2+) with these substrates yielding [Cu(I)(bpy)2](+) and [Cu(I)(phen)2](+) imply that these complexes undergo reduction-induced ligand dissociation reactions (phen = 1,10-phenanthroline). The average −N═N– lengths in mer-1(2+)[PF6(–)]2 and ctc-2(2+)[PF6(–)]2 are 1.248(4), while that in 3(+)[PF6(–)]·2CH2Cl2 is relatively longer, 1.275(2) Å, due to dCu → πazo* back bonding. In cyclic voltammetry, mer-1(2+) exhibits one quasi-reversible wave at −0.42 V due to Cu(II)/Cu(I) and abpy/abpy(•–) couples and two reversible waves at −0.90 and −1.28 V due to abpy/abpy(•–) couple, while those of ctc-2(2+) ion appear at −0.44, −0.86, and −1.10 V versus Fc(+)/Fc couple. The anodic 3(2+)/3(+) and the cathodic 3(+)/3 redox waves at +0.33 and −0.40 V are reversible. The electron paramagnetic resonance spectra and density functional theory (DFT) calculations authenticated the existence of abpy anion radical (abpy(•–)) in 3, which is defined as a hybrid state of [Cu(I)(abpy(0.5•–))(abpy(0.5•–))] and [Cu(II)(abpy(•–))(abpy(•–))] states. 3(2+) ion is a neutral abpy complex of copper(II) of type [Cu(II)(abpy)2](2+). 3 exhibits a near-IR absorption band at 2400–3000 nm because of the intervalence ligand-to-ligand charge transfer, elucidated by time-dependent DFT calculations in CH2Cl2.

Ruthenium, osmium and rhodium complexes of 1,4-diaryl 1,4-diazabutadiene: radical versus non-radical states

Molecular and electronic structures of the ruthenium, osmium and rhodium complexes of 1,4-di(3-nitrophenyl)-1,4-diazabutadiene (L^DAB) and their redox series are reported.