Suman Kundu

Synthesis, structure and DNA binding studies of 9-phenyldibenzo[a,c] phenazin-9-ium

The reaction of phenanthrene-9,10-dione with N-phenylbenzene-1,2-diamine in methanol in the presence of anhydrous CuCl2 and HCl affords a 9-phenyldibenzo[a,c]phenazin-9-ium cation, [1]+, as in [1][CuCl2], in good yields. The reaction of [1][CuCl2] in methanol with excess iodide salt affords [1][I]. The formations of [1][CuCl2] and [1][I] have been confirmed by elemental analyses, mass, IR, UV-vis and 1H NMR spectra including the single crystal X-ray structure determination of [1][CuCl2]. DNA binding studies by UV-vis spectra, fluorescence spectra, circular dichroism spectra, hydrodynamic, isothermal titration calorimetric (ITC), UV optical melting and gel electrophoresis experiments have substantiated that [1]+, like ethidium bromide, is a strong DNA intercalator.

Orthometalation of Dibenzo[1,2]quinoxaline with Ruthenium(II/III), Osmium(II/III/IV), and Rhodium(III) Ions and Orthometalated [RuNO]6/7 Derivatives

A new family of organometallics of ruthenium(II/III), osmium(II/III/IV), and rhodium(III) ions isolated from C-H activation reactions of dibenzo[1,2]quinoxaline (DBQ) using triphenylphosphine, carbonyl, and halides as coligands is reported. The CN-chelate complexes isolated are trans-[Ru(III)(DBQ)(PPh3)2Cl2] (1), trans-[Ru(II)(DBQ)(CO)(PPh3)2Cl] (2), trans-[Os(III)(DBQ)(PPh3)2Br2] (3), trans-[Os(II)(DBQ)(PPh3)2(CO)Br] (4), and trans-[Rh(III)(DBQ)(PPh3)2Cl2] (5). Reaction of 1 with NO affords trans-[Ru(DBQ)(NO)(PPh3)2Cl]Cl (6(+)Cl(-)), isoelectronic to 2, with a byproduct, [Ru(NO)(PPh3)2Cl3] (7). Complexes 1-5 and 6(+) were characterized by elemental analyses, mass, IR, NMR, and electron paramagnetic resonance (EPR) spectra including the single-crystal X-ray structure determinations of 1-3 and 5. The Ru(III)-C, Ru(II)-C, Os(III)-C, and Rh(III)-C lengths are 2.049(2), 2.074(3), 2.105(16), and 2.012(3) Å in 1, 2, 3, and 5. In cyclic voltammetry, 2, 3, and 4 undergo oxidation at 0.59, 0.39, and 0.46 V, versus Fc(+)/Fc couple, to trans-[Ru(III)(DBQ)(CO)(PPh3)2Cl](+) (2(+)), trans-[Os(IV)(DBQ)(PPh3)2Br2](+) (3(+)), and trans-[Os(III)(DBQ)(CO)(PPh3)2Br](+) (4(+)) ions. Complex 3(+) incorporates an Os(IV)(d(4) ion)-C bond. The 6(+)/trans-[Ru(DBQ)(NO)(PPh3)2Cl] (6) reduction couple at -0.65 V is reversible. 2(+), 3(+), 4(+) and 6 were substantiated by spectroelectrochemical measurements, EPR spectra, and density functional theory (DFT) and time-dependent (TD) DFT calculations. The frozen-glass EPR spectrum of the electrogenerated 6 exhibits hyperfine couplings due to (99,101)Ru and (14)N nuclei. DFT calculations on trans-[Os(III)(DBQ)(PMe3)2Br2] (3(Me)), St = 1/2 and trans-[Os(IV)(DBQ)(PMe3)2Br2](+) (3(Me+)), St = 0, trans-[Ru(DBQ)(NO)(PMe3)2Cl](+) (6(Me+)), St = 0 and trans-[Ru(DBQ)(NO)(PMe3)2Cl] (6(Me)), St = 1/2, authenticated a significant mixing between dOs and πaromatic* orbitals, which stabilizes M(II/III/IV)-C bonds and the [RuNO](6) and [RuNO](7) states, respectively, in 6(+) and 6, which is defined as a hybrid state of trans-[Ru(II)(DBQ)(NO(•))(PPh3)2Cl] and trans-[Ru(I)(DBQ)(NO(+))(PPh3)2Cl] states.

Mono- and di-nuclear photoluminescent complexes of zinc(II), cadmium(II) and mercury(II) of a chiral diimine ligand

Reaction of α-pyridoin and N-phenyl-o-phenylenediamine affords 2-(2-(phenylamino)phenylimino)-1,2-di(pyridin-2-yl)ethanol (L) which undergoes cyclization to a chiral diimine, 2-methoxy-1-phenyl-2,3-di(pyridin-2-yl)-1,2-dihydroquinoxaline, L(OMe) (conjugated 14πe system) in the presence of zinc(II), cadmium(II) and mercury(II) ions affording [Zn(L(OMe))Cl2] (1), [Cd2(L(OMe))2Cl4] (2) and [Hg2(L(OMe))2Cl4] (3) complexes. Ligand L and complexes 1-3 are substantiated by elemental analyses, mass, IR, (1)H NMR and UV-vis spectra including the single-crystal X-ray structures of 1 and 3. The possibility of the atropisomerism of L is restricted in cyclic L(OMe). L and complexes 1-3 are fluorescent in fluid solutions at 298 K (CH2Cl2: 1, λ(ex) = 470 nm, λ(em) = 627 nm, Φ = 0.014, τ(avg) = 2.5 ns; 2, λ(ex) = 430 nm, λ(em) = 599 nm, Φ = 0.08, τ(avg) = 7.6 ns; 3, λ(ex) = 415 nm, λ(em) = 600 nm, Φ = 0.021, τ(avg) = 2.8 ns). Time-resolved emission spectra (TRES) established that the two-component lifetimes of 1-3 are due to the existence of two conformers. Density functional theory (DFT) and time dependent (TD) DFT calculations authenticated that 1-3 complexes are fluorescent due to intra-ligand charge transfer (ILCT) to the π(diimines)* orbital.

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.

Molecular and Electronic Structures of Ruthenium Complexes Containing an ONS-Coordinated Open-Shell π Radical and an Oxidative Aromatic Ring Cleavage Reaction

The coordination chemistry of 2,4-di-tert-butyl-6-[(2-mercaptophenyl)amino]phenol (LONSH3), which was isolated as a diaryl disulfide form, (LONSH2)2, with a Ru ion is disclosed. It was established that the trianionic LONS3- is redox-noninnocent and undergoes oxidation to either a closed-shell singlet (CSS), LONS-, or an open-shell π-radical state, LONS•2-, and the reactivities of the [RuII(LONS•2-)] and [RuII(LONS-)] states are different. The reaction of (LONSH2)2 with [Ru(PPh3)3Cl2] in toluene in the presence of PPh3 affords a ruthenium complex of the type trans-[Ru(LONS)(PPh3)2Cl] (1), while the similar reaction with [Ru(PPh3)3(H)(CO)Cl] yields a LONS•2- complex of ruthenium(II) of the type trans-[RuII(LONS•2-)(PPh3)2(CO)] (2). 1 is a resonance hybrid of the [RuII(LONS-)Cl] and [RuIII(LONS•2-)Cl] states. It is established that 2 incorporating an open-shell π-radical state, [RuII(LONS•2-)(CO)], reacts with an in situ generated superoxide ion and promotes an oxidative aromatic ring cleavage reaction, yielding a α-N-arylimino-ω-ketocarboxylate (LNS2-) complex of the type [RuII(LNS2-)(PPh3)(CO)]2 (4), while 1 having a CSS state, [RuII(LONS-)Cl], is inert in similar conditions. Notably, 2 does not react with O2 molecule but reacts with KO2 in the presence of excess PPh3, affording 4. The redox reaction of (LONSH2)2 with [Ru(PPh3)3Cl2] in ethanol in air is different, leading to the oxidation of LONS to a quinone sulfoxide derivative (LONSO0) as in cis-[RuII(LONSO0)(PPh3)Cl2] (3), via 1 as an intermediate. The molecular and electronic structures of 1-4 were established by single-crystal X-ray crystallography, electron paramagnetic resonance spectroscopy, electrochemical measurements, and density functional theory calculations. 1+ is a resonance hybrid of [RuIII(LONS-)(PPh3)2Cl ↔ RuIV(LONS•2-)(PPh3)2Cl]+ states, 2- is a LONS3- complex of ruthenium(II), [RuII(LONS3-)(PPh3)2(CO)]-, and 2+ is a ruthenium(II) complex of LONS- of the type [RuII(LONS-)(PPh3)2(CO)]+, where 35% diradical character of the LONS- ligand was predicted.

Proton-Coupled Oxidation of a Diarylamine: Amido and Aminyl Radical Complexes of Ruthenium(II)

Diarylamido, Q-N--Py (L-), complexes of ruthenium(II), trans-[(L-H+)RuII(PPh3)2Cl2] (1-H+) and trans-[(L-)RuII(PPh3)2(CO)Cl] (2), using N-(5-nitropyridin-2-yl)quinolin-8-amine (HL) as a ligand are disclosed (Q and Py refer to quinoline and 5-nitropyridine fragments). 1-H+ contains a zwitterionic amido ligand (Q-N--PyH+) that undergoes a concerted proton electron transfer (CPET) reaction in air, generating trans-[(L)Ru(PPh3)2Cl2] (1·CH2Cl2). The ground electronic state of 1 is delocalized as [(L-)RuIII ↔ (L•)RuII] (L• is an aminyl radical of type Q-N•-Py). The 1-H+/1 redox potential depends on the electrolytes, and the potentials are -1.57 and -1.40 V, respectively, in the presence of [N( n-Bu)4]PF6 and [N( n-Bu)4]Cl. The rate of 1-H+ → 1 conversion depends also on the medium and follows the order kD2O-CH2Cl2 > kH2O-CH2Cl2 > kCH2Cl2. In contrast, 2 containing the corresponding amido (L-) is stable and endures oxidation at 0.14 V, affording trans-[(L•)RuII(PPh3)2(CO)Cl] (2+). The electronic structures of the complexes were authenticated by single-crystal X-ray diffraction studies of HL, 1·CH2Cl2, and 2·(toluene), EPR spectroscopy, and density functional theory (DFT) calculations. Notably, the CQ-N (1.401(2) Å) and CPy-N (1.394(2) Å) lengths in 1·CH2Cl2 are relatively longer than the CQ-Namido (1.396(4) Å)and CPy-Namido (1.372(4) Å) lengths in 2·(toluene). Spin density obtained from DFT calculations scatters on both N and ruthenium atoms, revealing a delocalized state of 1. The notion was further confirmed by variable-temperature EPR spectra of a powder sample and CH2Cl2 solution, where the contributions of both [(L-)RuIII] and [(L•)RuII] components were detected. In contrast, 2+ is an aminyl radical complex of ruthenium(II), where the spin is dominantly localized on the ligand backbone (64%), particularly on N (27%). 2+ exhibits a strong EPR signal at g = 2.003. 1 and 2+ exhibit absorption bands at 560-630 and 830-840 nm, and the origins of these excitations were elucidated by TDDFT calculations on 1 and 2 in CH2Cl2.