Cyclometalated ruthenium(II) complexes of benzo[h]quinoline (bzqH)[Ru(bzq)(NCMe)4], [Ru(bzq)(LL)(NCMe)2], and [Ru(bzq)(LL)2] (LL = bpy, phen)

Cyclometalation of benzo[h]quinoline (bzqH) by [RuCl(μ-Cl)(η⁶-C₆H₆)]₂ in acetonitrile occurs in a similar way to that of 2-phenylpyridine (phpyH) to afford [Ru(bzq)(MeCN)₄]PF₆ (3) in 52% yield. The properties of 3 containing ‘non-flexible’ benzo[h]quinoline were compared with the corresponding [Ru(phpy)(MeCN)₄]PF₆ (1) complex with ‘flexible’ 2-phenylpyridine. The [Ru(phpy)(MeCN)₄]PF₆ complex is known to react in MeCN solvent with ‘non-flexible’ diimine 1,10-phenanthroline to form [Ru(phpy)(phen)(MeCN)₂]PF₆, being unreactive toward ‘flexible’ 2,2′-bipyridine under the same conditions. In contrast, complex 3 reacts both with phen and bpy in MeCN to form [Ru(bzq)(LL)(MeCN)₂]PF₆ {LL = bpy (4) and phen (5)}. Similar reaction of 3 in methanol results in the substitution of all four MeCN ligands to form [Ru(bzq)(LL)₂]PF₆ {LL = bpy (6) and phen (7)}. Photosolvolysis of 4 and 5 in MeOH occurs similarly to afford [Ru(bzq)(LL)(MeCN)(MeOH)]PF₆ as a major product. This contrasts with the behavior of [Ru(phpy)(LL)(MeCN)₂]PF₆, which lose one and two MeCN ligands for LL = bpy and phen, respectively. The results reported demonstrate a profound sensitivity of properties of octahedral compounds to the flexibility of cyclometalated ligand. Analogous to the 2-phenylpyridine counterparts, compounds 4-7 are involved in the electron exchange with reduced active site of glucose oxidase from Aspergillus niger. Structure of complexes 4 and 6 was confirmed by X-ray crystallography.     

Versatile coordination behaviour of Ph2AsCH2AsPh2 with Ru(II)

Treatment of ‘RuCl₃ · 3H₂O’ with Ph₂AsCH₂AsPh₂ (dpam) in hot EtOH gives either trans-[RuCl₂(dpam-As,As′)(dpam-As)₂] (1), or cis-[RuCl₂(dpam-As,As′)₂] (2), depending on the mole ratio. On exposure to light, solutions of 2 isomerise to trans-[RuCl₂(dpam-As,As′)₂] (3). Treatment of [RuCl₂(PPh₃)₃] with two equivalents of dpam in CH₂Cl₂ gave a mixture of two products, from which trans-[RuCl₂(PPh₃) (dpam-As,As′)(dpam-As)] (4) was isolated by recrystallisation. The crystal structures of 1-4 are reported. Complexes 1-3 in CH₂Cl₂ undergo electrochemical oxidation to Ru(III), and the Ru(III) form of 2 undergoes isomerisation on the voltammetric timescale to the Ru(III) form of 3.     

Synthesis, structure, and characterization of some ruthenium arene complexes of N-(arylmethylene)-2-(methylthio)anilines and 2-(methylthio)aniline

A series of cationic, half-sandwich ruthenium complexes with the general formula [(η⁶-p-cymene)RuCl(MeSC₆H₄2-NCHAr)][PF₆] (3a-h), have been prepared from the reaction of [(η⁶-p-cymene)RuCl₂]₂ with various N,S-donor Schiff base ligands derived from 2-(methylthio)aniline and several substituted benzaldehydes. The related aniline complex [(η⁶-p-cymene)RuCl(MeS-C₆H₄-2-NH₂)][PF₆] (4) was synthesized from 2-(methylthio)aniline. All of the ruthenium complexes were characterized by IR, ¹H NMR, and UV/Vis spectroscopies. The molecular structure of complex 4 was determined by X-ray crystallography.     

Unusual ruthenium hydride complexes supported by the [N(2-PPh2-4-Me-C6H3)2] pincer ligand

Complexes of Ru(II) containing the pincer ligand [⁻N(2-PPh₂-4-Me-C₆H₃)₂] (PNP^Ph) were prepared. The complex (PNP^PhH)RuCl₂ (1) was treated with 2 equiv AgOTf to produce the triflate complex (PNP^PhH)Ru(OTf)₂ (2). Complex 1 was also treated with an excess of NaBH₄ to give a bimetallic complex [(PNP^Ph)RuH₃]₂ (3). A number of methods, including X-ray crystallography, NMR spectroscopy, and computational studies, were used to probe the structure of 3. Addition of Lewis bases to 3 resulted in octahedral complexes containing a hydride ligand trans to a dihydrogen ligand.     

Spectral properties and bio-activity of copper(II) clofibriates, part III: crystal structure of Cu(clofibriate)2(2-pyridylmethanol)2, Cu(clofibriate)2(4-pyridylmethanol)2(H2O) dihydrate, and Cu2(clofibriate)4(N,N-diethylnicotinamide)2

New copper(II) clofibriates (clof, {2-(4-chlorophenoxy)-2-methylpropionic or 2-(4-chlorophenoxy)isobutyric acid}) of composition Cu(clof)₂L₂ (where L=2-pyridylmethanol (2-pymeth) (1), N-methylnicotinamide (Menia) (4), N,N-diethylnicotinamide (Et₂nia) (5), isonicotinamide (isonia) (7) or methyl-3-pyridylcarbamate (mpc) (8)), [Cu(clof)₂(4-pymeth)₂(H₂O)] · 2H₂O (4-pymeth=4-pyridylmethanol) (2 · 2H₂O) and Cu(clof)₂L (where L=4-pymeth (3) or Et₂nia (6)) have been prepared and spectroscopically characterized. All the Cu(clof)₂L₂ compounds seem to possess distorted octahedral copper(II) stereochemistry with differing tetragonal distortions. An X-ray analysis of 1 was carried out and it featured a tetragonal-bipyramidal geometry around the copper(II) atom. X-ray analysis of 2 · 2H₂O featured a square-pyramidal geometry around copper(II) atom. Both the Cu(clof)₂L compounds seem to consist of a binuclear unit of tetracarboxylate type bridging. An X-ray analysis of 6 revealed typical binuclear paddle-wheel type structure, consisting of two copper(II) atoms in square-pyramidal geometry bridged by four carboxylate anions in the xy-plane. All complexes under study were characterized by EPR and electronic spectroscopy. The antimicrobial effects have been tested on various strains of bacteria, yeasts and filamentous fungi.     

Ligand effects in cis-Ru(N-N)2L2 species where N-N is a substituted 2,2′-bisoxazoline and L is monodentate

Starting from previously reported cis-Ru(MeL)₂Cl₂, where MeL is 4,4,4′,4′-tetramethyl-2,2′-bisoxazoline, cis-Ru(MeL)₂Br₂ (1), cis-Ru(MeL)₂I₂ (2), cis-Ru(MeL)₂(NCS)₂ · H₂O (3), cis-Ru(MeL)₂(N₃)₂ (4) and cis-[Ru(MeL)₂(MeCN)₂](PF₆)₂ · (CH₃)₂CO (5) are synthesised. The X-ray crystal structures of complexes 1, 2, 3 and 5 have been determined. All the five new complexes have been characterized by FTIR, ESIMS and ¹H NMR. In cyclic voltammetry in acetonitrile at a glassy carbon electrode, the complexes display a quasireversible Ru(II/III) couple in the range 0.32-1.71 V versus NHE. The Ru(II/III) potentials yield a satisfactorily linear correlation with Chatt’s ligand constants P_L for the monodantate ligands. From the intercept and by comparing the known situation in Ru(2,2′-bipyridine)₂L₂, it is concluded that MeL, a non-aromatic diimine, is significantly more π-acidic than 2,2′-bipyridine.     

Synthesis, structure and reactivity of complexes containing [M(S2)2] fragments (M=Ru, Os; (S2)=1,2-benzenedithiolate (2−))

Subsequent addition of 1,2-benzenedithiol (S₂-H₂) and nBuLi to a solution of [Ru(NO)Cl₃ · xMeOH] in THF afforded exclusively the monomeric species NBu₄[Ru^II(NO)(S₂)₂] (1). Formation of dimeric (NBu₄)₂[Ru^II(NO)(S₂)₂]₂ (2) has been confirmed when the deprotonated ligand S₂-Li₂ was added to [Ru(NO)Cl₃ · xMeOH] and allowed to stir for 30 h. The monomer 1 undergoes aerial oxidation to give (NBu₄)₂[Ru^IV(S₂)₃] (3). The reaction between RuCl₃ · xH₂O and S₂-H₂ in the presence of NaOMe, afforded the dinulear Ru^III species (NMe₄)₂[Ru^III(S₂)₂]₂ (4). A modified method for the preparation of 1 is being employed to synthesize the osmium analogue NBu₄[Os(NO)(S₂)₂] (5) effectively. The solid state structures of 1, 2 and 3 were determined by X-ray crystal structure analysis. A comparison of relevant bond distance data suggests that 1,2-benzenedithiolate acts as an “innocent” ligand.     

Unexpected formation and structure elucidation of mer-[RuCl3(TMSO)(bpy)] derived from [H(TMSO)][trans-RuCl4(TMSO)2] under mild condition

Treatment of [H(TMSO)][trans-RuCl₄(TMSO)₂] (1) with 2,2′-bipyridine (bpy) in ethanol at room temperature resulted an unknown mer-[RuCl₃(TMSO)(bpy)] (3) and a known cis-[RuCl₂(TMSO)₄] (4) (TMSO =  tetramethylene sulfoxide) complexes. The 3 was obtained by the substitution with bpy in mer-[RuCl₃(TMSO)₃] (2), whereas 4 was obtained by one-electron reduction of 2, suggesting that 2 is a precursor for both 3 and 4. The structure of 3 was determined by single crystal X-ray diffraction. The reaction is a new synthetic procedure for 3 and/or 3 and 4 in mild reaction conditions from the anionic complex 1. It involves simultaneous substitution and redox reaction. This is the first known example of precisely characterized Ru(III)-chloride-TMSO-bpy-complex derived from anionic [H(TMSO)][trans-RuCl₄(TMSO)₂] at room temperature.     

Cu(II) complexes with square pyramidal (N2S)CuCl2 chromophore: Jahn-Teller distortion and subsequent effect on spectral and structural properties

One monomeric neutral Cu(II) complex [(pmtpm)CuCl₂] (1) is reported by Lindoy and Livingstone [8]. Two new complexes namely, μ-Cl bridged binuclear Cu(II) complex [{(pmtpm)Cu(Cl)}₂ μ-Cl](ClO₄) (2) and a bis μ-Cl bridged binuclear Cu(II) complex [{(pmtpm)Cu}₂(μ-Cl)₂](ClO₄)₂ (3) derived from a tridentate Schiff base ligand, 2-pyridyl-N-(2′-methylthiophenyl)methyleneimine (pmtpm) were synthesized and characterized by various spectroscopic methods and by X-ray crystallography. (N₂S)CuCl₂ chromophore(s) of distorted square pyramidal coordination geometries around Cu(II) ion(s) have been observed for all the complexes 1-3. The equatorial sites of the square plane comprise two N and a thioether S donor atoms of the pmtpm ligand as well as one Cl⁻ ion (terminal in 1 and 2, and bridging in 3) while the remaining axial site is occupied by a terminal Cl⁻ ion (for 1) or a bridging Cl⁻ ion (for 2 and 3). The equatorial Cu-Cl distances are much shorter [1: 2.2511(4) Å, 2: 2.2307(12) Å, 3: 2.2513(12) Å] than the axial Cu-Cl distances [1: 2.4394(4) Å, 2: 2.5597(9) Å, 3: 2.7037(12) Å]. The correlation of an axial Cu-Cl bond elongation with a lower g_|| value in the solid state EPR spectrum and a blue shifted ligand field transition in the solid and solution phase absorption spectrum has been observed.     

Short-bite aminobis(phosphonite) containing olefinic functionalities, PhN{P(OC6H3(OMe-o)(C3H5-p))2}2: Synthesis and transition metal complexes

Short-bite aminobis(phosphonite) containing olefinic functionalities, PhN{P(OC₆H₃(OMe-o)(C₃H₅-p))₂}₂ (1) was synthesized by reacting PhN(PCl₂)₂ with eugenol in the presence of triethylamine. The ligand 1 acts as a bidentate chelating ligand toward metal complexes [M(CO)₄(C₅H₁₀NH)₂] forming [M(CO)₄{η²-PhN{P(OC₆H₃(OMe-o)(C₃H₅-p))₂}₂}] (M = Mo, 2; W, 3). The reaction between 1 and [CpFe(CO)₂]₂ leads to the cleavage of one of the P-N bonds due to the metal assisted hydrolysis to give a mononuclear complex [CpFe(CO){P(O)(OC₆H₃(OMe-o)(C₃H₅-p))₂}{PhN(H)(P(OC₆H₃(OMe-o)(C₃H₅-p))₂)}] (4). Treatment of 1 with gold(I) derivative, [AuCl(SMe₂)] resulted in the formation of a dinuclear complex, [(AuCl)₂{PhN{P(OC₆H₃(OMe-o)(C₃H₅-p))₂}₂}] (5) with a Au···Au distance of 3.118(2) Å indicating the possibility of aurophilic interactions. An equimolar reaction between 1 and [Ru(η⁶-p-cymene)Cl₂]₂ afforded a tri-chloro-bridged bimetallic complex [(η⁶-p-cymene)Ru(μ-Cl)₃Ru{PhN(P(OC₆H₃(OMe-o)(C₃H₅-p))₂)₂}Cl] (6). The crystal structures of 1-3 and 5 were established by single crystal X-ray diffraction studies.     

Supramolecular assemblies of new 2-D complexes: Syntheses, crystal structures, spectroscopic and magnetic properties of {[MnAu2(CN)4(NITpPy)2(H2O)2]}n and {[Co(N(CN)2)2(NITpPy)2(H2O)2]}n

Two new complexes, {[MnAu₂(CN)₄(NITpPy)₂(H₂O)₂]}_n (1) and {[Co(N(CN)₂)₂(NITpPy)₂(H₂O)₂]}_n (2), have been synthesized and characterized. The single-crystal X-ray analysis for the complexes 1 and 2 demonstrates that each M(II) (M = Mn or Co) ion assumes a distorted octahedral MN₄O₂ coordination polyhedron. Four nitrogen atoms come from the cyanide groups and the pyridyl rings in a common plane, and two oxygen atoms come from the H₂O molecules in trans-positions. The structures of complexes 1 and 2 illustrate that aurophilicity and/or hydrogen bonding interactions play important roles in increasing dimensionality. Magnetic investigations on complexes 1 and 2 show the presence of weak antiferromagnetic interactions.     

Ruthenium(II/III) mediated transformation of 1,2-bis(2′-pyridylmethyleneimino)benzene (L) to 2-(2′-benzimidazolyl)pyridine (L′H) and its in situ formed complexes with Ru(II): X-ray structure of trans-[Ru(PPh3)2(L′H)2](ClO4)2

A series of ruthenium (II) complexes of formulae trans-[Ru(PPh₃)₂(L′H)₂](ClO₄)₂ (1), [Ru(bpy)(L′H)₂](ClO₄)₂ (2), [Ru(bpy)₂(L′H)](ClO₄)₂ (3), cis-[Ru(DMSO)₂(L′H)₂]Cl₂ (4), and [Ru(L′H)₃](PF₆)₂ (5) (where L′H = 2-(2′-benzimidazolyl)pyridine) have been synthesized by reaction of the appropriate ruthenium precursor with 1,2-bis(2′-pyridylmethyleneimino)benzene (L). The complexes were characterized by elemental analyses, spectroscopic and electrochemical data. All the complexes were found to be diamagnetic and hence metal is in +2 oxidation state. The molecular structure of trans-[Ru(PPh₃)₂(L′H)₂](ClO₄)₂ has been determined by the single crystal X-ray diffraction studies. The molecular structure shows that Ru(II) is at the center of inversion of an octahedron with N₄P₂ coordination sphere. The ligand acts as a bidentate N,N′donor. The electronic spectra of the complexes display intense MLCT bands in the visible region.Cyclic voltammetric studies show quasi-reversible oxidative response at 0.99-1.32 V (vs Ag/AgCl reference electrode) due to Ru(III)/Ru(II) couple.     

p-Quinquephenyl diamine, C6H5-p-C6H4-p-C6H2(2,3-NH2)-p-C6H4-C6H5, and its corresponding diimine-Ru(II) complex: Crystal structure and electrochemical and optical properties

The molecular structure of an o-phenylenediamine unit-containing oligophenylene (1), Ph-Ph′-Ph′(2,3-NH₂)-Ph′-Ph (Ph = phenyl; Ph′ = p-phenylene; Ph′(2,3-NH₂) = 2,3-diamino-p-phenylene), was determined by X-ray crystallography. 1 has a twisted structure, and forms an intermolecular C-H?π interaction network. The -NH₂ group of 1 was air-oxidized to an imine, NH, group in the presence of [RuCl₂(bpy)₂] (bpy = 2,2′-bipyridyl) and gave a ruthenium(II)-benzoquinone diimine complex [Ru(2)(bpy)₂](PF₆)₂ (2: Ph-Ph′-Ph′(2,3-imine)-Ph′-Ph). The molecular structure of [Ru(2)(bpy)₂](PF₆)₂ was confirmed by X-ray crystallography. [Ru(2)(bpy)₂](PF₆)₂ underwent two-step electrochemical reduction with E^1/2 = −0.889 V and −1.531 V versus Fc⁺/Fc. The E^1/2’s were located at higher potentials by 91 mV and 117 mV, respectively, than those of reported [Ru(bqdi)(bpy)₂](PF₆)₂ (bqdi = benzoquinone diimine). Electrochemical oxidation of [Ru(2)(bpy)₂](PF₆)₂ occurred at a lower potential by 180 mV than that of [Ru(bqdi)(bpy)₂](PF₆)₂. Occurrence of the easier reduction and oxidation of [Ru(2)(bpy)₂](PF₆)₂ than those of [Ru(bqdi)(bpy)₂](PF₆)₂ is ascribed to the presence of a large π-conjugation system in 2.     

Coordination polymers of 1,8-bis(2-methylthioethoxy)anthraquinone and 1,5-bis(2-methylthioethoxy)anthraquinone with Ag(I): Synthesis and X-ray crystallography

The reaction of 2-(methylthioethanol) with 1,8-dichloroanthraquinone and 1,5-dichloroanthraquinone in THF with base produces 1,8-bis(2-methylthioethoxy)anthraquinone (1) and 1,5-bis(2-methylthioethoxy)anthraquinone (2), respectively. Silver(I) complexes of 1 and 2 have been synthesized after combination with [Ag(CH₃CN)₄]BF₄ in 1:1 M ratio to yield, [(1,8-bis(2-methylthioethoxy)anthraquinone)Ag]BF₄, (3) and [(1,5-bis(2-methylthioethoxy)anthraquinone)Ag·CH₃CN]BF₄, (4). X-ray crystal structures of the free ligand (1) and the Ag(I) complexes (3 and 4) are reported. The intraannular carbonyl group forms a coordinate-covalent bond with Ag(I) and, in the solid state, both silver(I) complexes are found as coordination polymers.     

Syntheses and structures of the heterometallic clusters [(Ph3PAu)3Re(CO)4], [(Ph3PAu)4Re(CO)4], [(Ph3PAu)6AuRe2(CO)8], and [(Ph3PAu)6Re(CO)3]

The reaction of [HRe₃(CO)₁₂]²⁻ with an excess of Ph₃PAuCl in CH₂Cl₂ yields [(Ph₃PAu)₄Re(CO)₄]⁺ as the main product, which crystallizes as [(Ph₃PAu)₄Re(CO)₄]PF₆ · CH₂Cl₂ (1 · CH₂Cl₂) after the addition of KPF₆.The crystal structure determination reveals a trigonal bipyramidal Au₄Re cluster with the Re atom in equatorial position.If [(Ph₃PAu)₄Re(CO)₄]⁺ is reacted with PPh₄Cl, a cation [Ph₃PAu]⁺ is eliminated as Ph₃PAuCl, and the neutral cluster [(Ph₃PAu)₃Re(CO)₄] (2) is formed.It combines with excess [(Ph₃PAu)₄Re(CO)₄]⁺ to afford the cluster cation, [(Ph₃PAu)₆AuRe₂(CO)₈]⁺. It crystallizes from CH₂Cl₂ as[(Ph₃PAu)₆AuRe₂(CO)₈]PF₆ · 4CH₂Cl₂ (3 · 4CH₂Cl₂). In [(Ph₃PAu)₃Re(CO)₄] the metal atoms are arranged in form of a lozenge while in [(Ph₃PAu)₆AuRe₂(CO)₈]⁺ two Au₄Re trigonal bipyramids are connected by a common axial Au atom.The treatment of [(Ph₃PAu)₄Re(CO)₄]⁺ with KOH and Ph₃PAuCl in methanol yields the cluster cation [(Ph₃PAu)₆Re(CO)₃]⁺, which crystallizes with from CH₂Cl₂ as [(Ph₃PAu)₆Re(CO)₃]PF₆ · CH₂Cl₂ (4 · CH₂Cl₂). The metal atoms in this cluster form a pentagonal bipyramid with the Re atom in the axial position.     

Electronic effects on the interactions of complexes [Ru(phen)2(p-L)] (L=MOPIP, HPIP, and NPIP) with DNA

In order to explore the electronic effects of Ru(II) complexes binding to DNA, a series of Ru(II) complexes [Ru(phen)₂ (p-MOPIP)]²⁺ (1), [Ru(phen)₂ (p-HPIP)]²⁺ (2), and [Ru(phen)₂(p-NPIP)]²⁺ (3) were synthesized and characterized by elementary, ¹H NMR, and ES-MS analysis. The binding properties of these complexes to CT-DNA were investigated with spectroscopic methods and viscosity experiments. Furthermore, the computations for these complexes applying the density functional theory (DFT) method have also been performed. The results show that all of these complexes can well bind to DNA in intercalation mode and DNA-binding affinity of these complexes is greatly influenced by electronic effects of intercalating ligands. The intrinsic binding constants for 1, 2, and 3 are 0.20, 0.69, and 1.56 × 10⁵ M⁻¹, respectively. This order is in accordance with that of the electron-withdrawing ability of substituent [-OR < -OH < -NO₂]. Such a trend in electronic effects of Ru(II) complexes binding to DNA can be reasonably explained by the DFT calculations.     

fac-/mer-[RuCl3(NO)(P-N)] (P-N = [o-(N,N-dimethylamino)phenyl]diphenylphosphine): Synthesis, characterization and DFT calculations

Complex fac-[RuCl₃(NO)(P-N)] (1) was synthesized from the reaction of [RuCl₃(H₂O)₂(NO)] and the P-N ligand, o-[(N,N-dimethylamino)phenyl]diphenylphosphine) in refluxing methanol solution, while complex mer,trans-[RuCl₃(NO)(P-N)] (2) was obtained by photochemical isomerization of (1) in dichloromethane solution. The third possible isomer mer,cis-[RuCl₃(NO)(P-N)] (3) was never observed in direct synthesis as well as in photo- or thermal-isomerization reactions. When refluxing a methanol solution of complex (2) a thermally induced isomerization occurs and complex (1) is regenerated.The complexes were characterized by NMR (³¹P{¹H}, ¹⁵N{¹H} and ¹H), cyclic voltammetry, FTIR, UV-Vis, elemental analysis and X-ray diffraction structure determination. The ³¹P{¹H} NMR revealed the presence of singlet at 35.6 for (1) and 28.3 ppm for (2). The ¹H NMR spectrum for (1) presented two singlets for the methyl hydrogens at 3.81 and 3.13 ppm, while for (2) was observed only one singlet at 3.29 ppm. FTIR Ru-NO stretching in KBr pellets or CH₂Cl₂ solution presented 1866 and 1872 cm⁻¹ for (1) and 1841 and 1860 cm⁻¹ for (2). Electrochemical analysis revealed a irreversible reduction attributed to Ru^II-NO⁺ → Ru^II-NO⁰ at −0.81 V and −0.62 V, for (1) and (2), respectively; the process Ru^II → Ru^III, as expected, is only observed around 2.0 V, for both complexes.Studies were conducted using ¹⁵NO and both complexes were isolated with ¹⁵N-enriched NO. Upon irradiation, the complex fac-[RuCl₃(NO)(P-N)] (1) does not exchange ¹⁴NO by ¹⁵NO, while complex mer,trans-[RuCl₃(NO)(P-N)] (2) does. Complex mer,trans-[RuCl₃(¹⁵NO)(P-N)] (2′) was obtained by direct reaction of mer,trans-[RuCl₃(NO)(P-N)] (2) with ¹⁵NO and the complex fac-[RuCl₃(¹⁵NO)(P-N)] (1′) was obtained by thermal-isomerization of mer,trans-[RuCl₃(¹⁵NO)(P-N)] (2′).DFT calculation on isomer energies, electronic spectra and electronic configuration were done. For complex (1) the HOMO orbital is essentially Ru (46.6%) and Cl (42.5%), for (2) Ru (57.4%) and Cl (39.0%) while LUMO orbital for (1) is based on NO (52.9%) and is less extent on Ru (38.4%), for (2) NO (58.2%) and Ru (31.5%).     

Interactions of arene-Ru(II)-chloroquine complexes of known antimalarial and antitumor activity with human serum albumin (HSA) and transferrin

The interactions of π-arene-Ru(II)-chloroquine complexes with human serum albumin (HSA), apotransferrin and holotransferrin have been studied by circular dichroism (CD) and UV-Visible spectroscopies, together with isothermal titration calorimetry (ITC). The data for [Ru(η⁶-p-cymene)(CQ)(H₂O)Cl]PF₆ (1), [Ru(η⁶-benzene)(CQ)(H₂O)Cl]PF₆ (2), [Ru(η⁶-p-cymene)(CQ)(H₂O)₂][PF₆]₂ (3), [Ru(η⁶-p-cymene)(CQ)(en)][PF₆]₂ (4), [Ru(η⁶-p-cymene)(η⁶-CQDP)][BF₄]₂ (5) (CQ: chloroquine; DP: diphosphate; en: ethylenediamine), in comparison with CQDP and [Ru(η⁶-p-cymene)(en)Cl][PF₆] (6) as controls demonstrate that 1, 2, 3, and 5, which contain exchangeable ligands, bind to HSA and to apotransferrin in a covalent manner. The interaction did not affect the α-helical content in apotransferrin but resulted in a loss of this type of structure in HSA. The binding was reversed in both cases by a decrease in pH and in the case of the Ru-HSA adducts, also by addition of chelating agents. A weaker interaction between complexes 4 and 6 and HSA was measured by ITC but was not detectable spectroscopically. No interactions were observed for complexes 4 and 6 with apotransferrin or for CQDP with either protein. The combined results suggest that the arene-Ru(II)-chloroquine complexes, known to be active against resistant malaria and several lines of cancer cells, also display a good transport behavior that makes them good candidates for drug development.     

Trans-cis-cis-[RuCl2(DMSO)2(2-amino-5-methyl-thiazole)2], (PMRu52), a novel ruthenium(II) compound acting as a strong inhibitor of cathepsin B

A novel ruthenium(II) compound, trans-cis-cis-[Ru(II)Cl₂(DMSO)₂(2-amino-5-methyl-thiazole)₂], (I), PMRu52 hereafter, that may be obtained from the previously described (cis and trans)-[Ru(II)Cl₂(DMSO)₄] complexes, was designed, synthesized and characterised. The single crystal X-ray structure shows a roughly regular octahedral environment for the ruthenium(II) center with the two chloride ligands in trans and the other two pairs of identical ligands in cis. The behaviour of PMRu52 in phosphate buffer, at pH = 7.4, was characterised spectroscopically as well as its interactions with a few representative biomolecules. Tight ruthenium binding to serum albumin was established by joint use of spectroscopic and separation methods. Afterward, the reactions of PMRu52 with the model proteins ubiquitin and cytochrome c were monitored through electrospray ionisation mass spectrometry (ESI-MS) methods: the formation of metallodrug-protein adducts was documented in detail and the fragmentation patterns of PMRu52 were defined. Finally, the ability of PMRu52 to affect the activity of cathepsin B, a well known cysteine protease, was evaluated in vitro and a pronounced enzyme inhibition highlighted, with an IC₅₀ value of 5.5 μM. This latter finding is of particular interest as cathepsin B constitutes an attractive “druggable” target for cancer, rheumatoid arthritis and other important diseases.     

Carboxylate and dicarboxylate derivatives of [Et4N][Re2(CO)6(OR)3] (R = H or Me)

The ligand exchange reaction of the anionic binuclear rhenium complexes (R = H (1) or Me (2)) has been studied with the carboxylic acids; benzoic acid (3, 4, and 5), fumaric acid (6), and terephthalic acid (7). The exchange with benzoic acid can be controlled by stoichiometry to one, two, or three substitutions. The doubly (4) and triply (5) substituted complexes represent new structural motifs for the triply bridged Re₂(CO)₆ unit. The dicarboxylic acids fumaric and terephthalic bridge two dirhenium centers. Crystal structure determinations have been carried out for the new complexes synthesized.