Ruthenium(II) complexes of aroylhydrazones: structural,electrochemical and electrostatic interactions with DNA

Four Ru(II) complexes with tridentate ligands viz. (4-hydroxy-N′-(pyridin-2-yl-ethylene) benzohydrazide [Ru(L¹)(PPh₃)₂(Cl)] (1), N′-(pyridin-2-yl-methylene) nicotinohydrazide [Ru(L²)(PPh₃)₂(Cl)] (2), N′-(1H-imidazol-2-yl-methylene)-4-hydroxybenzohydrazide [Ru(L³)(PPh₃)₂(Cl)] (3), and N′-(1H-imidazol-2-yl-methylene) nicotinohydrazide [Ru(L⁴)(PPh₃)₂(Cl)] (4) have been synthesized and characterized. The methoxy-derivative of L³H (abbreviated as L³H*) exists in E configuration with torsional angle of 179.4° around C₇-N₈-N₉-C₁₀ linkage. Single crystal structures of acetonitrile coordinated ruthenium complexes of 1 and 3 having compositins as [Ru(L¹)(PPh₃)₂(CH₃CN)]Cl (1a) and [Ru(L³)(PPh₃)₂(CH₃CN)]Cl (3a) revealed coordination of tridentate ligands with significantly distorted octahedral geometry constructed by imine nitrogen, heterocyclic nitrogen, and enolate amide oxygen, forming a cis-planar ring with trans-placement of two PPh₃ groups and a coordinated acetonitrile. Ligands (L¹H-L⁴H) and their ruthenium complexes (1–4) are characterized by ¹H, ¹³C, ³¹P NMR, and IR spectral analysis. Ru(II) complexes have reversible to quasi-reversible redox behavior having Ru(II)/Ru(III) oxidation potentials in the range of 0.40–0.71 V. The DNA binding constants determined by absorption spectral titrations with Herring Sperm DNA (HS-DNA) reveal that L⁴H and 1 interact more strongly than other ligands and Ru(II) complexes. Complexes 1–3 exhibit DNA cleaving activity possibly due to strong electrostatic interactions while 4 displays intercalation.     

Four mono-/bi-nuclear palladium(II) complexes of triphenylphosphine and heterocyclic-N/NS ligands: Synthesis, structural characterization and luminescence properties

The reactions of palladium(II) chloride, PPh₃ and heterocyclic-N/NS ligand in a mixture of CH₃CN (5 ml) and CH₃OH (5 ml) produced [PdCl₂(PPh₃)(L1)]·(CH₃CN) (1) (L1 = ADMT = 3-amino-5,6-dimethyl-1,2,4-triazine), [PdCl₂(PPh₃)(L2)] (2) (L2 = 3-CNpy = 3-cyanopyridine), [PdCl(PPh₃)(L3)]₂·(CH₃CN) (3), [PdCl(PPh₃)₂(HL3)]Cl (4) (HL3 = Hmbt = 2-mercaptobenzothiazole). The coordination geometry around the Pd atoms in these complexes is a distorted square plane. In 3, L3 acts as a bidentate ligand, bridging two metal centers, while in 4, HL3 appears as monodentate ligand with one nitrogen donor atom uncoordinated. Complexes 1-4 are characterized by IR, luminescence, NMR and single crystal X-ray diffraction analysis. All complexes exhibit luminescence in solid state at room temperature.     

Nucleophilic addition of water to coordinated dipyridylethylene in rhenium(V) complexes

Complexes of general formula [ReOX₂{(C₅H₄N)CH(O)CH₂(C₅H₄N)}] (X?=?Cl,?I) were prepared by reaction of trans-[ReOCl₃(PPh₃)₂] and trans-[ReOI₂(OEt)(PPh₃)₂] with cis-1,2-di-(2-pyridyl)ethylene (DPE) in ethanol and benzene in air. The coordinated DPE ligand undergoes addition of water at the ethylenic carbon atoms, and the (C₅H₄N)CH(O)CH₂(C₅H₄N) moiety acts as a uninegative terdentate N,O,N-donor ligand. X-ray crystal structures of both complexes have been determined and show distorted octahedral geometry at the rhenium(V) centre.     

Studies of η5-cyclichydrocarbon ruthenium(II) complexes containing para-amino-N-(pyrid-2-ylmethylene)phenylamine ligand: molecular structure of [(η5-C5H5)Ru(PPh3)(C5H4NCH=N-C6H4-p-NH2)]BF4

Reaction of [(η⁵-Cp)Ru(PPh₃)₂Cl] (1) with excess para-amino-N-(pyrid-2-ylmethylene)-phenylamine ligand (app) in methanol in the presence of NH₄BF₄ leads to the formation of [η⁵-CpRu(PPh₃)(aap)]BF₄ (6BF₄). Similarly, [(η⁵-ind)Ru(PPh₃)₂(CH₃CN)]BF₄ (4BF₄) and [(η⁵-Cp*)Ru(PPh₃)₂(CH₃CN)]BF₄ (5BF₄) react with app to yield the cationic complexes [(η⁵-ind)Ru(PPh₃)(app)]BF₄ (7BF₄) and [(η⁵-Cp*)Ru(PPh₃)(app)]BF₄ (8BF₄), respectively. The complexes were characterized by analysis and spectroscopic data. The structure of a representative complex (6BF₄) was established by single-crystal X-ray methods.     

Metal Derivatives of Heterocyclic‐2‐thiones: Crystal Structures of [Bis(diphenylphosphanyl)propane][bis(pyrimidine‐2‐thiolato)]ruthenium(II) and [Bis(diphenylphosphanyl)methane][bis(pyridine‐2‐thiolato)]ruthenium(II)

Ruthenium(II) Complexes containing pyrimidine‐2‐thiolate (pymS^–) and bis(diphenylphosphanyl)alkanes [Ph₂P–(CH₂)_m–PPh₂, m = 1, dppm; m = 2, dppe; m = 3, dppp; m = 4, dppb] are described. Reactions of [RuCl₂L₂] (L = dppm, dppp) and [Ru₂Cl₄L₃] (L = dppb) with pyrimidine‐2‐thione (pymSH) in 1:2 molar ratio in dry benzene in the presence of Et₃N base yielded the [Ru(pymS)₂L] complexes (pymS^– = pyrimidine‐2‐thiolate; L = dppm ( 1 ); dppp ( 3 ); dppb ( 4 )). The complex [Ru(pymS)₂(dppe)] ( 2 ) was indirectly prepared by the reaction of [Ru(pymS)₂(PPh₃)₂] with dppe. These complexes were characterized using analytical data, IR, ¹H, ¹³C, ³¹P NMR spectroscopy, and X‐ray crystallography (complex 3 ). The crystal structure of the analogous complex [Ru(pyS)₂(dppm)] ( 5 ) with the ligand pyridine‐2‐thiolate (pyS^–) was also described. X‐ray crystallographic investigation of complex 3 has shown two four‐membered chelate rings (N, S donors) and one six‐membered ring (P, P donors) around the metal atom. Compound 5 provides the first example in which Ru^II has three four‐membered chelate rings: two made up by N, S donor ligands and one made up by P, P donor ligand. The arrangement around the metal atoms in each complex is distorted octahedral with cis:cis:trans:P, P:N, N:S, S dispositions of the donor atoms. The ³¹P NMR spectroscopic data revealed that the complexes are static in solution, except 2 , which showed the presence of more than one species.     

(PPh4)2[MoN(N3)3Cl]2; Synthese,IR-Spektrum und Kristallstruktur

(PPh₄)₂[MoN(N₃)₃Cl]₂; Synthesis, IR Spectrum, and Crystal Structure The title compound is formed in the reaction of molybdenum (II) benzoate with trimethylsilyl azide and PPh₄Cl in dichloro methane forming dark red single crystals. A PPh₃Me⊕ salt of the ion [MoN(N₃)₃Cl]₂^2? is obtained from (PPh₃Me)₂MoNCl₄] treated with silver azide in CH₂Cl₂ suspension. The solvent CH₂Cl₂ participates in both reactions as oxidizing agent. (PPh₄)₂[MoN(N₃)₃Cl₂ is characterized by a structural analysis based upon X-ray data: space group P1 , Z = 1, a = 1050.7 pm; b = 1185.4 pm; c = 1190.8 pm; α = 98.90°; β = 106.87°; γ = 103.97° (4505 independent, observed reflexions, R = 0.039). The compound consists of PPh₄⊕ cations and centrosymmetric anions [MoN(N₃)₃Cl₂^2? in which the molybdenum atoms are bridged by the N_α atoms of two azide groups; the resulting Mo? N bond lengths are 208 pm and 260 pm. In trans position to the long Mo? N bond the terminal nitrido ligand is situated, the Mo?N distance of 164 pm corresponds to a triple bond. Two terminal azido ligands and the chloro ligand are filling up the coordination sphere of the molybdenum atoms to a coordination number of six. The i.r. spectrum is reported and assigned.     

Stereospecific synthesis and redox properties of ruthenium(II) carbonyl complexes bearing a redox-active 1,8-naphthyridine unit

Two stereoisomers of cis-[Ru(bpy)(pynp)(CO)Cl]PF₆ (bpy = 2,2′-bipyridine, pynp = 2-(2-pyridyl)-1,8-naphthyridine) were selectively prepared. The pyridyl rings of the pynp ligand in [Ru(bpy)(pynp)(CO)Cl]⁺ are situated trans and cis, respectively, to the CO ligand. The corresponding CH₃CN complex ([Ru(bpy)(pynp)(CO)(CH₃CN)]²⁺) was also prepared by replacement reactions of the chlorido ligand in CH₃CN. Using these complexes, ligand-centered redox behavior was studied by electrochemical and spectroelectrochemical techniques. The molecular structures of pynp-containing complexes (two stereoisomers of [Ru(bpy)(pynp)(CO)Cl]PF₆ and [Ru(pynp)₂(CO)Cl]PF₆) were determined by X-ray structure analyses.     

Synthese und Eigenschaften von (Acido)(nitrosyl)phthalocyaninato(2–)ruthenium

Synthesis and Properties of (Acido)(nitrosyl)phthalocyaninato(2–)ruthenium (Acido)(nitrosyl)phthalocyaninato(2–)ruthenium, [Ru(X)(NO)pc^2–] (X = F, Cl, Br, I, CN, NCO, NCS, NCSe, N₃, NO₂) is obtained by acidification of a solution of bis(tetra(n-butyl)ammonium) bis(nitro)phthalocyaninato(2–)ruthenate(II) in tetrahydrofurane with the corresponding conc. mineral acid or aqueous ammonium salt solution. The nitrite-nitrosyl conversion is reversal in basic media. The cyclic and differential pulse voltammograms show mainly three quasi-reversible one-electron processes at 1.05, –0.65 and –1.25 V, ascribed to the first ring oxidation and the stepwise reduction to the complexes of type {RuNO}⁷ and {RuNO}⁸, respectively. The B < Q < N regions in the electronic absorption spectra are still typical for the pc^2– ligand, but are each split into two strong absorptions (14500/16500(B); 28000/30500(Q); 34500/37000 cm^–1(N)), whose relative intensities strongly depend on the nature of the axial ligand X. In the IR spectra is active the N–O stretching vibration between 1827 (X = I) and 1856 cm^–1 (F), the C–N stretching vibration at 2178 (X = NCO), 2072 (NCS), 2066 (NCSe), 2093 cm^–1 (CN), the N–N stretching vibration of the azide ligand at 2045 cm^–1, the fundamentals of the nitrito(O) ligand at 1501, 932, and 804 cm^–1, and the Ru–X stretching vibration at 483 (F), 332 (Cl), 225 (Br), 183 (I), 395 (N₃), 364 (ONO), 403 (CN), 263 (NCS), and 231 cm^–1 (NCSe). In the resonance Raman spectra, excited in coincidence with the B region, the Ru–NO stretching vibration and the very intense Ru–N–O deformation vibration are selectively enhanced between 580 and 618 cm^–1, and between 556 and 585 cm^–1, respectively.     

Redox,spectroscopic, photo-induced ligand exchange,and DNA interaction studies of a new Ru(II)Pt(II) bimetallic complex

A new bimetallic complex, [Ru(biq)₂(dpp)PtCl₂](PF₆)₂ (where biq = 2,2′-biquinoline and dpp = 2,3-bis(2-pyridyl)pyrazine), containing a cis-PtCl₂ moiety coupled to a sterically strained Ru(II)-based chromophore was designed, synthesized, and investigated with respect to its spectroscopic, redox, photo-induced ligand exchange, and DNA-interaction properties. The electrochemistry of the designed complex was found to be consistent with the bridging coordination of the dpp ligand and formation of the bimetallic complex. The complex displays intense ligand-based π → π* transitions in the UV region and metal-to-ligand charge-transfer transitions (MLCT) in the visible region. The loss of bridging coordination of the dpp ligand and formation of complexes, [Ru(biq)₂(CH₃CN)₂]²⁺ and [Pt(dpp)(CH₃CN)₂]²⁺ was observed when an acetonitrile solution of the metal complex was irradiated with visible light (λ_irr ≥ 550 nm). The designed complex displays covalent binding with DNA in dark through the cis-PtCl₂ moiety, as confirmed by agarose gel electrophoresis. Upon photoirradiation, the complex dissociates into two DNA-binding moieties and displays covalent binding through: (i) a cis-PtL₂ subunit of [Ptdpp(L)₂]²⁺ and (ii) open coordination sites of the ruthenium of [Ru(biq)₂(L)₂]²⁺ (L = solvent). The designed complex represents the first Ru(II)Pt(II) complex that undergoes photo-induced ligand exchange and displays multifunctional interactions with DNA upon photoirradiation.     

Darstellung und Kristallstrukturen von Ag[N(CN)2](PPh3)2, Cu[N(CN)2](PPh3)2 und Ag[N(CN)2](PPh3)3

Preparation and Crystal Structures of Ag[N(CN)₂](PPh₃)₂, Cu[N(CN)₂](PPh₃)₂, and Ag[N(CN)₂](PPh₃)₃ The coordination compounds Ag[N(CN)₂](PPh₃)₂ ( 1 ), Cu[N(CN)₂](PPh₃)₂ ( 2 ), and Ag[N(CN)₂](PPh₃)₃ ( 3 ) are obtained by the reaction of AgN(CN)₂ or CuN(CN)₂ with triphenylphosphane in CH₂Cl₂. X‐ray structure determinations were performed on single crystals of 1 , 2 , and 3 · C₆H₅Cl. The three compounds crystallize monoclinic in the space group P2₁/n with the following unit cell parameters. 1 : a = 1216.07(9), b = 1299.5(2), c = 2148.4(3) pm, β = 99.689(13)°, Z = 4; 2 : a = 1369.22(10), b = 1257.29(5), c = 1888.04(15) pm, β = 94.395(7)°, Z = 4; 3 · C₆H₅Cl: a = 1276.6(4), b = 1971.7(3), c = 2141.3(5) pm, β = 98.50(3)°, Z = 4. In all structures the metal atoms have a distorted tetrahedral coordination. The crystal structure of 3 · C₆H₅Cl shows monomeric molecular units with terminal coordinated dicyanamide. The crystal structure of 1 is built up by dinuclear units, which are bridged by dicyanamide ligands. However, the crystal structure of 2 corresponds to a onedimensional coordination polymer, bridged by dicyanamide anions.     

Studies on the reactivity of cis-RuCl2 fragment in Ru(PPh3)2(TaiMe)Cl2 with N,N-chelators (TaiMe = 1-methyl-2-(p-tolylazo)imidazole). Spectral and electrochemical characterisation of the products

Dechlorination of Ru(PPh₃)₂(TaiMe)Cl₂ (TaiMe = p-Me-C₆H₄-N=N-C₃H₂NN(1)-Me (1), 1-methyl-2-(p-tolylazo)imidazole) has been carried out in acetone solution by Ag⁺ and reacted with N,N’-chelators to synthesise [Ru(PPh₃)₂ (TaiMe)(N,N’)]²⁺. The complexes have been isolated as their perchlorate salts. The N,N’ chelators are 1-alkyl-2-(phenylazo)imidazoles (PaiX, X = Me, Et, CH₂Ph); 2-(arylazo)pyridines, (Raap,p-R-C₆H₄-N=N-C₅H₄N; R = H, Me, Cl); 2-(arylazo)pyrimidines (Raapm,p-R-C₆H₄-N=N-C₃N₂H₂; R = H, Me, Cl); 2,2’-bipyridine (bpy) and 1,10-phenanthroline (o-phen). Unsymmetrical N,N’ chelators may give two isomers and this is indeed observed. The¹H NMR spectral data refer to the presence of two isomers in the mixture in different proportions. With consideration of coordination pairs in the order of PPh₃, PPh₃; N,N (N refers to N(immidazole)) and N’,N (N’ refers to N(azo)), the complexes have been characterised astrans-cis-cis andtrans-trans-trans configuration; the former predominates in the mixture. Electrochemical studies exhibit high potential Ru(III)/Ru(II) couple and quasireversible N=N reduction. Electronic spectra show high intensity (ε ∼ 10⁴) MLCT transition in the visible region (520 ±10) nm along with a shoulder (ε ∼ 10³) in the longer wavelength region.     

Ruthenium(II) complexes with 2-(benzylimino-methyl)-4-R-phenol containing the trans(PPh3),cis(CO,Cl)-{Ru(PPh3)2(CO)Cl} unit

Reactions of [Ru(PPh₃)₃Cl₂] with 2-(benzylimino-methyl)-4-R-phenol (H^RL, R = H, Cl, Br and OMe) in boiling methanol in presence of triethylamine afford ruthenium(II) complexes of general formula [Ru(^RL)(PPh₃)₂(CO)Cl] in 57-64% yield. Microanalysis, spectroscopic (infrared, electronic and NMR) and cyclic voltammetric measurements have been used for the characterization of the complexes. Crystal structures of two representative complexes have been determined by X-ray crystallography. The carbonyl, the chloride, the N,O-donor ^RL⁻ and the two mutually trans PPh₃ molecules assemble a distorted octahedral CClNOP₂ coordination sphere around the metal centre in each complex. The complexes display the Ru(II) → Ru(III) oxidation in the potential range 0.62-1.16 V (vs. Ag/AgCl).     

Synthesis,structural characterization,oxygen sensitivity,and antimicrobial activity of ruthenium(II) carbonyl complexes with thiosemicarbazones

[Ru(CO)(PPh₃)₂(η³-O,N³,S-TSC¹)] (1), [Ru(Cl)(CO)(PPh₃)₂(η²-N³,S-TSC²)] (2), and [Ru(Cl)(CO)(PPh₃)₂(η²-N³,S-TSC³)] (3) have been prepared by reacting [Ru(H)(Cl)(CO)(PPh₃)₃] with the respective thiosemicarbazones TSC¹ (2-hydroxy-3-methoxybenzaldehyde thiosemicarbazone), TSC² (3-hydroxybenzaldehyde thiosemicarbazone), and TSC³ (3,4-dihydroxybenzaldehyde thiosemicarbazone) in a 1?:?1 M ratio in toluene and all of the complexes have been characterized by UV–vis, FT-IR, and ¹H and ³¹P NMR spectroscopy. The spectroscopic studies showed that TSC¹ is coordinated to the central metal as a tridendate ligand coordinating via the azomethine nitrogen (C=N), phenolic oxygen, and sulfur to ruthenium in 1, whereas TSC² and TSC³ are coordinated to ruthenium as a bidentate ligand through azomethine nitrogen (C=N) and sulfur in 2 and 3. Oxygen sensitivities of 1–3 and [Ru(Cl)(CO)(PPh₃)₂(η²-N³,S-TSC⁴)] (4), and antimicrobial activities of 1–3 have been determined.     

Synthesis,structure and properties of three one-dimensional coordination polymers {[M(II)L(NCS)2](DMF)2} n (M(II)=cadmium(II), zinc(II), manganese(II); L=1,4-bis[2-(2-pyridyl)benzimidazolato]butane)

A tetradentate N-donor ligand 1,4-bis[2-(2-pyridyl)benzimidazolato]butane (L) was prepared for construction of a coordination framework. Three one-dimensional coordination polymers {[M(II)L(NCS)₂](DMF)₂} _n (M(II) = cadmium(II), 1, zinc(II), 2, manganese(II), 3) were obtained by reaction of metal ions and L in the presence of KSCN in DMF/water. The complexes are isostructural and consist of 1D zigzag [M(II)L(NCS)₂] _n chains and DMF molecules. Within the chains, the metal atoms are each octahedrally coordinated by four N atoms of L and two N atoms of the SCN^? anions. Complexes 1 and 2 in the solid state at room temperature exhibit intense photoluminescence at 453 and 433 nm, respectively.     

Synthesis,spectroscopy and structure of cis,cis,trans:N,N;P,P;S,S-[bis(triphenylphosphine)] [bis(pyrimidine-2-thiolato)]ruthenium(II)

Reaction of RuCl₂(PPh₃)₃with pyrimidine-2-thione (HpymS) in a 1:2?mol ratio in dry benzene in the presence of triethylamine as base yielded a complex of stoichiometry [Ru(pymS)₂(PPh₃)₂] (1). This has been characterized using analytical data and IR, ¹H, ¹³C and ³¹P NMR spectroscopy. ¹H NMR confirmed the deprotonation of HpymS. ³¹P NMR spectra showed a single peak confirming equivalent P atoms. Complex 1 crystallizes in space group Pī and HpymS acts as a η²-N,S-deprotonated bidentate anionic ligand. The coordination geometry around the Ru center is distorted octahedral with cis dispositions of P atoms, as well as two N atoms of pymS^– and trans S atoms of pymS^–. Important bond distances and angles are: Ru–N, 2.119(2), 2.106(2); Ru–S, 2.4256(8), 2.4413(8); and Ru–P, 2.3266(7), 2.3167(7)?Å; P(2)–Ru(1)–P(1), 96.07(3); N(21)–Ru(1)–N(11), 83.46(9); and S(1)–Ru(1)–S(2), 153.02(3)°.     

Regiospecific solvent-free transfer hydrogenation of α,β-unsaturated carbonyl compounds catalyzed by a cationic ruthenium(II) compound

[(PPh₃)₂Ru(CH₃CN)₃Cl][BPh₄] has been found to catalyze the selective reduction of double bonds in α,β-unsaturated ketones with high conversions when formic acid is the hydrogen donor.     

Nickel(II) Complexes of Pentadentate N5 Ligands as Catalysts for Alkane Hydroxylation by Using m‐CPBA as Oxidant: A Combined Experimental and Computational Study

A new family of nickel(II) complexes of the type [Ni(L)(CH₃CN)](BPh₄)₂, where L=N‐methyl‐N,N′,N′‐tris(pyrid‐2‐ylmethyl)‐ethylenediamine (L1, 1 ), N‐benzyl‐N,N′,N′‐tris(pyrid‐2‐yl‐methyl)‐ethylenediamine (L2, 2 ), N‐methyl‐N,N′‐bis(pyrid‐2‐ylmethyl)‐N′‐(6‐methyl‐pyrid‐2‐yl‐methyl)‐ethylenediamine (L3, 3 ), N‐methyl‐N,N′‐bis(pyrid‐2‐ylmethyl)‐N′‐(quinolin‐2‐ylmethyl)‐ethylenediamine (L4, 4 ), and N‐methyl‐N,N′‐bis(pyrid‐2‐ylmethyl)‐N′‐imidazole‐2‐ylmethyl)‐ethylenediamine (L5, 5 ), has been isolated and characterized by means of elemental analysis, mass spectrometry, UV/Vis spectroscopy, and electrochemistry. The single‐crystal X‐ray structure of [Ni(L3)(CH₃CN)](BPh₄)₂ reveals that the nickel(II) center is located in a distorted octahedral coordination geometry constituted by all the five nitrogen atoms of the pentadentate ligand and an acetonitrile molecule. In a dichloromethane/acetonitrile solvent mixture, all the complexes show ligand field bands in the visible region characteristic of an octahedral coordination geometry. They exhibit a one‐electron oxidation corresponding to the Ni^II/Ni^III redox couple the potential of which depends upon the ligand donor functionalities. The new complexes catalyze the oxidation of cyclohexane in the presence of m‐CPBA as oxidant up to a turnover number of 530 with good alcohol selectivity (A/K, 7.1–10.6, A=alcohol, K=ketone). Upon replacing the pyridylmethyl arm in [Ni(L1)(CH₃CN)](BPh₄)₂ by the strongly σ‐bonding but weakly π‐bonding imidazolylmethyl arm as in [Ni(L5)(CH₃CN)](BPh₄)₂ or the sterically demanding 6‐methylpyridylmethyl ([Ni(L3)(CH₃CN)](BPh₄)₂ and the quinolylmethyl arms ([Ni(L4)(CH₃CN)](BPh₄)₂, both the catalytic activity and the selectivity decrease. DFT studies performed on cyclohexane oxidation by complexes 1 and 5 demonstrate the two spin‐state reactivity for the high‐spin [(N5)Ni^II?O^.] intermediate (ts1_hs, ts2_doublet), which has a low‐spin state located closely in energy to the high‐spin state. The lower catalytic activity of complex 5 is mainly due to the formation of thermodynamically less accessible m‐CPBA‐coordinated precursor of [Ni^II(L5)(OOCOC₆H₄Cl)]⁺ ( 5 a ). Adamantane is oxidized to 1‐adamantanol, 2‐adamantanol, and 2‐adamantanone (3°/2°, 10.6–11.5), and cumene is selectively oxidized to 2‐phenyl‐2‐propanol. The incorporation of sterically hindering pyridylmethyl and quinolylmethyl donor ligands around the Ni^II leads to a high 3°/2° bond selectivity for adamantane oxidation, which is in contrast to the lower cyclohexane oxidation activities of the complexes.     

Syntheses,characterization, and crystal structures of ruthenium(II)/(III) complexes with tridentate salicylaldiminato ligands

Treatment of [Ru(PPh₃)₃Cl₂] with one equivalent of tridentate Schiff base 2-[(2-dimethylamino-ethylimino)-methyl]-phenol (HL) in the presence of triethylamine afforded a ruthenium(III) complex [RuCl₃(κ²-N,N-NH₂CH₂CH₂NMe₂)(PPh₃)] as a result of decomposition of HL. Interaction of HL and one equivalent of [RuHCl(CO)(PPh₃)₃], [Ru(CO)₂Cl₂] or [Ru(tht)₄Cl₂] (tht = tetrahydrothiophene) under different conditions led to isolation of the corresponding ruthenium(II) complexes [RuCl(κ³-N,N,O-L)(CO)(PPh₃)] (2), [RuCl(κ³-N,N,O-L)(CO)₂] (3), and a ruthenium(III) complex [RuCl₂(κ³-N,N,O-L)(tht)] (4), respectively. Molecular structures of 1·CH₂Cl₂, 2·CH₂Cl₂, 3 and 4 have been determined by single-crystal X-ray diffraction.     

A new polypyridyl-based Ru (II) complex as a highly efficient electrocatalyst for CO2 reduction

A new polypyridyl Ru (II) complex, cis-[Ru (Me₄phen)₂(CH₃CN)₂](NO₃)₂ (Me₄phen = 3,4,7,8-tetramethyl-1,10-phenanthroline) has been prepared and fully characterized by elemental analysis, X-ray crystallography, cyclic voltammetry and spectroscopic techniques. The solid-state structure of the complex indicated that the Ru (II) center is sitting in an N₄N′₂ coordination environment with a distorted octahedral geometry. Cyclic voltammetry technique was used to investigate the catalytic activity of the Ru (II) complex on the electrocatalytic reduction of CO₂ to CO in acetonitrile. The effect of the different reaction parameters, including the scan rate, concentration of the electrocatalyst [complex Ru (II)] and reaction temperature, on the catalytic activity was also investigated. The results showed that the electrocatalytic activity of the complex increases with increasing electrocatalyst concentration and scan rate. Further, the CO₂ reduction peak current decreases at lower temperatures owing to the inverse relationship between the temperature and activation energy. The theoretical calculations confirmed the proposed electrocatalytic mechanism comprising seven steps.     

Photocytotoxicity and photoinduced phosphine ligand exchange in a Ru(ii) polypyridyl complex

Two new tris-heteroleptic Ru(ii) complexes with triphenylphosphine (PPh₃) coordination, cis-[Ru(phen)₂(PPh₃)(CH₃CN)]²⁺ (1a, phen = 1,10-phenanthroline) and cis-[Ru(biq)(phen)(PPh₃)(CH₃CN)]²⁺ (2a, biq = 2,2′-biquinoline), were synthesized and characterized for photochemotherapeutic applications. Upon absorption of visible light, 1a exchanges a CH₃CN ligand for a solvent water molecule. Surprisingly, the steady-state irradiation of 2a followed by electronic absorption and NMR spectroscopies reveals the photosubstitution of the PPh₃ ligand. Phosphine photoinduced ligand exchange with visible light from a Ru(ii) polypyridyl complex has not previously been reported, and calculations reveal that it results from a trans-type influence in the excited state. Complexes 1a and 2a are not toxic against the triple negative breast cancer cell line MDA-MB-231 in the dark, but upon irradiation with blue light, the activity of both complexes increases by factors of >4.2 and 5.8, respectively. Experiments with PPh₃ alone show that the phototoxicity observed for 2a does not arise from the released phosphine ligand, indicating the role of the photochemically generated ruthenium aqua complex on the biological activity. These complexes represent a new design motif for the selective release of PPh₃ and CH₃CN for use in photochemotherapy.

New Ru(ii) complexes exhibit selective ligand dissociation driven by an excited state trans-type influence. The complexes are not toxic to triple-negative breast cancer cells in the dark, but induce cell death upon irradiation with visible light.