Reactivity studies of highly electrophilic ruthenium complexes

The 16-electron, coordinatively unsaturated, dicationic ruthenium complex [Ru(P(OH)₂(OMe))(dppe)₂][OTf]₂ (1a) brings about the heterolysis of the C-H bond in phenylacetylene to afford the phenylacetylide complex trans-[Ru(CCPh)(P(OH)₂(OMe))(dppe)₂][OTf] (2). The phenylacetylide complex undergoes hydrogenation to give a ruthenium hydride complex trans-[Ru(H)(P(OH)₂(OMe))(dppe)₂][OTf] (3) and phenylacetylene via the addition of H₂ across the Ru-C bond. The 16-electron complex also reacts with HSiCl₃ quite vigorously to yield a chloride complex trans-[Ru(Cl)(P(OH)₂(OMe))(dppe)₂][OTf] (4). On the other hand, the other coordinatively unsaturated ruthenium complex [Ru(P(OH)₃)(dppe)₂][OTf]₂ (1b) reacts with a base N-benzylideneaniline to afford a phosphonate complex [Ru(P(O)(OH)₂)(dppe)₂][OTf] (5) via the abstraction of one of the protons of the P(OH)₃ ligand by the base. The phenylacetylide, chloride, and the phosphonate complexes have been structurally characterized. The phosphonate complex reacts with H₂ to afford the corresponding dihydrogen complex trans-[Ru(η²-H₂)(P(O)(OH)₂)(dppe)₂][OTf] (5-H₂). The intact nature of the H-H bond in this species was established using variable temperature ¹H spin-lattice relaxation time measurements and the observation of a significant J(H,D) coupling in the HD isotopomer trans-[Ru(η²-HD)(P(O)(OH)₂)(dppe)₂][OTf] (5-HD).     

Coordination polymers and monomers based on new aminocarboxylate ligands: A cadmium(II) polymer containing dimeric aqua-bridged cadmium complex governed by polymeric chain

The synthesis and characterization of novel coordination polymers [Co(HCCB)(H₂O)₂]_n (1), [Zn(HCCB)(H₂O)₂]_n (2), {[Cd(HCCB)₂]·0.5[Cd(μ-H₂O)(H₂O)₄]₂}_n (3) and [Cu(HCCB)(H₂O)₂]_n (4) based on 3-(carboxymethylamino)-4-chlorobenzoic acid (H₃CCB) and mononuclear complexes [Cu(HBCCB)(H₂O)]·H₂O (5), [Co(HBCCB)(H₂O)]·H₂O (6), [Zn(HBCCB)(H₂O)] (7) and [Cd(HBCCB)(H₂O)] (8) containing 3-bis(carboxymethylamino)-4-chlorobenzoic acid (H₃BCCB) have been described. The compounds under investigation have been characterized by elemental analyses, spectral studies and structures of 1-3 and 5 determined crystallographically. Structural data of 1 and 2 revealed that the deprotonated HCCB²⁻ bridges metal centers leading to a double stranded 1D chain. On the other hand, the HCCB²⁻ coordinated thorough carboxylate oxygen and amino nitrogen in 3 to afford a 1D chain whose charge neutrality is maintained by inclusion of aqua-bridged dimer [{Cd(μ-H₂O)(H₂O)₄}₂]⁴⁺. Strong Cu?Cl interaction (2.754 Å) in 5 imposes a coordination geometry that is half-way between the square planar and square pyramidal. The H₃CCB, H₃BCCB and 1-3 and 5 are fluorescent at rt. Thermal studies (TG and DSC) on 1-3 suggested higher stability of 2 relative to 1 and 3 [ΔH_f (kcal/mol), ΔS_f = 152.17, 0.60, 1; 195.56: 0.86, 2; 69.33:0.36, 3].     

Synthesis and exploratory coordination chemistry of the new ditertiary carbinamine ligand 2,6-bis(α-aminoisopropyl)pyridine

The new pyridine-based N∩N∩N tridentate ligand 2,6-C₅H₃N(CMe₂NH₂)₂ (1) was synthesized by the treatment of 2,6-pyridinedicarbonitrile with an excess of the organocerium reagent in situ generated from CeCl₃ and methyllithium in THF. The reaction of 1 with [RuCl₂(PPh₃)₃] in THF at ambient conditions afforded (OC-6-23)-[RuCl{2,6-C₅H₃N(CMe₂NH₂)₂}(PPh₃)₂]Cl (2). The corresponding dimethyl sulfoxide complex [RuCl{2,6-C₅H₃N(CMe₂NH₂)₂}{S(O)Me₂}₂]Cl (3) was isolated as a mixture of the (OC-6-23) and (OC-6-32) stereoisomers 3a and 3b from the reaction between 1 and (OC-6-22)-[RuCl₂{S(O)Me₂}₃(OSMe₂)] in toluene at 80 °C. A prolonged interaction in toluene at reflux temperature gave isomerically pure 3a. The metal trichloride hydrates MCl₃ · xH₂O (M = Ru, Rh, Ir; x ≅ 2-4) produced mer-[RuCl₃{2,6-C₅H₃N(CMe₂NH₂)₂}] (M = Ru: 4; Rh: 5; Ir: 6), when combined with 1 in refluxing ethanol. The crystal structures of the following compounds were determined: ligand 1 and complexes 2-5 as addition compounds 2 · CH₂Cl₂, 3a · C₇H₈, 4 · EtOH and .     

Acidic 1,3-propanediaminetetraacetate zinc complexes as a probe of water soluble coordination polymers

In a very acidic solution, potassium 1,3-propanediaminetetraacetate zinc chloride K_2n[ZnCl₂(1,3-H₂pdta)ZnCl₂]_n (1) and its substituted iodide [ZnI₂(H₂O)(1,3-H₄pdta)]_n (2) (H₄pdta = 1,3-propanediaminetetraacetatic acid, C₁₁H₁₈N₂O₈) were isolated. The former was obtained from the reaction of zinc chloride and H₄pdta in pH ∼1.5. Further substitution of 1 results in the formation of iodide 2 with the addition of potassium iodide in acidic solution of pH 0.5. Complex 1 consists of a dimeric anionic unit [ZnCl₂(1,3-H₂pdta)ZnCl₂]²⁻ with strong intra-molecular hydrogen bonds [N1?O2 2.648(4); N1?O4 2.710(4) Å]. In neutral complex 2, an 1,3-pdta ligand links each monomeric unit [Zn(H₂O)I₂] to generate an infinite 1D chain, which extents into a 3D supramolecular structure by very strong inter-molecular hydrogen bonds the [O4?O2b 2.50 (1) Å, bx, y, z + 1]. 1 is soluble in water at room temperature, which is traced by ¹³C NMR experiment.     

The first report on specific binding mode of diethylmalonate acting as a bridging ligand between ruthenium (II) ions stabilized by intramolecular hydrogen bonds

Typically 2,2-diethylmalonate (dem) acts as a chelating ligand and binds to the metal in a η² (dem-O, O′) mode. However, when cis,fac-[RuCl₂(TMSO-S)₄] is treated with K₂(dem), it prefers to bind in an unusual bridging mode (μ-dem-O, O′) with the ruthenium (II) cation containing coordinated water, forming a strong hydrogen bond with the non-coordinated oxygen atoms of the 2,2-diethylmalonate ligand. The reaction products of cis,fac-[RuCl₂(TMSO-S)₄] (1) and cis,fac-[RuCl₂(DMSO-S)₃(DMSO-O)] (2) with dem are the dinuclear species with two bridging dem units, fac-[Ru(TMSO-S)₃(H₂O)(μ²-dem-O, O′)]₂ (3) and fac-[Ru(DMSO-S)₃(H₂O)(μ²-dem-O, O′)]₂ (4), respectively. The complex 3 was characterized by X-ray crystallography in which water ligands occupy anti positions with respect to each other. The NMR and X-ray study support each other with respect to dinuclear structure of 3 and 4, indicating that the dinuclear structure observed in the solid state is preserved in solution as well. The mononuclear anionic complex with chelating dem unit, K{fac-[RuCl(η²-dem-O, O′)(TMSO-S)₃} (5), was also isolated from the reaction of 1 and K₂(dem) demonstrating that 5 is an intermediate in the formation of 3.     

The unexpected reactions of [RuCl3(2mqn)NO] (H2mqn=2-methyl-8-quinolinol) with 2-chloro-8-quinolinol (H2cqn) and of [RuCl(2cqn)(2mqn)NO] on photoirradiation

The reaction of [RuCl₃(2mqn)NO]⁻ (H2mqn=2-methyl-8-quinolinol) with 2-chloro-8-quinolinol (H2cqn) afforded cis-1 [RuCl(2cqn)(2mqn)NO] (the oxygen of 2cqn is trans to the NO) (complex 1), cis-1 [RuCl(2cqn)(2mqn)NO] (the oxygen of 2mqn is trans to the NO) (complex 2) and a 1:1 mixture of cis-2 [RuCl(2cqn)(2mqn)NO] (the oxygen of 2mqn is trans to the NO) and cis-2 [RuCl(2cqn)(2mqn)NO] (the oxygen of 2cqn is trans to the NO) (complex 3). The reaction was compared with that of [RuCl₃(2mqn)NO]⁻ with 8-quinolinol (Hqn) or 5-chloro-8-quinolinol (H5cqn). Photoirradiation reaction of complex 1 at room temperature in deaerated CH₂Cl₂ in the presence of NO gave trans-[RuCl(2cqn)(2mqn)NO] (the Cl is trans to the NO) and complex 2 with recovery of complex 1. The reaction was contrasted with that of cis-1 [RuCl(qn)(2mqn)NO] or cis-1 [RuCl(5cqn)(2mqn)NO]. The crystal structure of complex 1 was determined by X-ray diffraction. The reactions were examined under consideration of atomic charge of the phenolato oxygen in 8-quinolinol and its derivatives calculated at the restricted Hartree-Fock/6-311G** level.     

Dinuclear ruthenium(II) catecholato and 2,3-naphthalenediolato complexes featuring κ-diaryloxo/η-arene coordination mode

A new dinuclear ruthenium(II) catecholato complex [Cp*Ru(κ²:η⁶-μ₂-1,2-O₂C₆H₄)RuCp*] (3; Cp* = η⁵-C₅Me₅) has been prepared by the reaction of [Cp*RuCl]₄ with 2 equiv. of disodium catecholate in THF. Complex 3 has a dinuclear structure, in which one of the Cp*Ru fragments is κ²-bonded to the two oxygen atoms and the other is η⁶-bonded to the aromatic ring. Similar treatment of [Cp*RuCl]₄ with disodium 2,3-naphthalenediolate affords an analogous κ²:η⁶-bonded dinuclear complex [Cp*Ru(κ²:η⁶-μ₂-2,3-O₂C₁₀H₆)RuCp*] (4) with selective π-complexation at the oxygen-substituted naphthalene ring. The molecular structure of 4 has been determined by X-ray crystallography. The oxygen-bound ruthenium atoms in complexes 3 and 4 are coordinatively unsaturated and readily uptake 1 equiv. of carbon monoxide to give the corresponding carbonyl adducts [Cp*Ru(CO)(κ²:η⁶-μ₂-1,2-O₂C₆H₄)RuCp*] (5) and [Cp*Ru(CO)(κ²:η⁶-μ₂-2,3-O₂C₁₀H₆)RuCp*] (6), respectively.     

Synthesis, structure and property of manganese(II) complexes with mixed tetradentate imidazole-containing ligand and benzenedicarboxylate

Three new coordination complexes [Mn(L)(H₂O)₂](1,4-BDC)·2H₂O (1), [Mn(L)_0.5(1,4-BDC)]CH₃OH·H₂O (2) and [Mn(L)(H₂O)₂](1,2-HBDC)₂·2H₂O (3) were synthesized by solvothermal reactions of 1,2,4,5-tetrakis(imidazol-1-ylmethyl)benzene (L) and 1,4-benzenedicarboxylic acid (1,4-H₂BDC) or 1,2-benzenedicarboxylic acid (1,2-H₂BDC) with Mn(II) salt, and characterized by single crystal X-ray diffraction, IR, thermogravimetric and elemental analyses. In complexes 1 and 3, each ligand L links four Mn(II) atoms to form two-dimensional (2D) cationic network with non-coordinated 1,4-BDC²⁻ and 1,2-HBDC⁻ anions lying in the voids between the two adjacent layers, respectively. The 2D layers are further connected together by hydrogen bonds to give three-dimensional (3D) supramolecular structures. However, the 1,4-BDC²⁻ in 2 acts not only as counteranion, but also as bridging ligand leading to the formation of 2-fold interpenetrated 3D framework with pcu (primitive cubic unit) topology. The Mn(II) atoms bridged by carboxylate groups in 2 show antiferromagnetic interactions.     

Mononuclear and dinuclear model hydrolases of nickel and cobalt

Reaction between the dinuclear model hydrolases [M₂(μ-OAc)₂(OAc)₂(μ-H₂O)(tmen)₂]; M = Ni (1); M = Co (2) and trimethylsilyltrifluoromethanesulphonate (TMS-OTf) under identical reaction conditions gives the mononuclear complex [Ni(OAc)(H₂O)₂(tmen)][OTf] · H₂O (3) in the case of nickel and the dinuclear complex [Co₂(μ-OAc)₂(μ-H₂O)₂(tmen)₂][OTf]₂ (4) in the case of cobalt.Reaction of (3) with urea gives the previously reported [Ni(OAc)(urea)₂(tmen)][OTf] (5), whereas (4) gives [Co₂(OAc)₃(urea)(tmen)₂][OTf] (6) previously obtained by direct reaction of (2) with urea. Both (3) and (4) react with monohydroxamic acids (RHA) to give the dihydroxamate bridged dinuclear complexes [M₂(μ-OAc)(μ-RA)₂(tmen)₂][OTf]; M = Ni (7); M = Co (8) previously obtained by the reaction of (1) and (2) with RHA, illustrating the greater ability of hydroxamic acids to stabilize dinuclear complexes over that of urea by means of their bridging mode, and offering a possible explanation for the inhibiting effect of hydroxamic acids by means of their displacing bridging urea in a possible intermediate invoked in the action of urease.     

A series of d transition metal coordination complexes: Structures and comparative study of surface electron behaviors (n = 9, 8, 7, 6, 5)

Ten transition metal coordination complexes [Cu₂(phen)(p-tpha)(μ-O)]_n1, [Cu(m-tpha)(imH)₂]_n2, [Ni(5-Haipa)₂(H₂O)₂]_n3, [Ni(phen)₂(H₂O)₂]·btc·[Ni(H₂O)₆]_0.5·9H₂O 4, [Co(2,5-pdc)(H₂O)₂]_n·nH₂O 5, [Co₂(2,5-pdc)₂(H₂O)₆]_n·2nH₂O 6, [Fe(2,5-Hpdc)₂(H₂O)₂]·H₂O 7, [Co(C₆H₄NO₂)₃]·H₂O 8, [Fe₂(μ₂-btec)(μ₂-H₂btec)(bipy)₂(H₂O)₂]_n9, [Mn(phen)(2,5-pdc)(H₂O)₂]·H₂O 10 (H₄btec = 1,2,4,5-benzenetetracarboxylic acid, phen = 1,10-phenanthroline, 2,5-H₂pdc = 2,5-pyridine-dicarboxylic acid, p-tpha = p-phthalic acid, m-tpha = m-phthalic acid, bipy = 2,2′-bipyridine, 5-H₂aipa = 5-aminoisophthalic acid, imH = imidazole, H₃btc = 1,3,5-benzenetricarboxylic acid) were synthesized through hydrothermal method. They were characterized by UV-Vis absorption spectra, single-crystal X-ray diffraction and surface photovoltage spectra (SPS). Structural analysis indicated that the complexes 1, 2, 3, 5, 6 and 9 were linked into infinite structures bridged by organic acid ligands. The other four complexes were molecular complexes and further connected to 2D or 3D structures by the hydrogen bonds. The SPS of complexes 1-10 indicate that there are positive response bands in the range of 300-800 nm showing different levels of photo-electric conversion properties. The intensity, position, shape and the number of the response bands in SPS are obviously different since the structure, species, valence, dⁿ electrons configuration and coordinated environment of the center metals are different. There are good relationships between SPS and UV-Vis spectra.     

Synthesis and characterisation of bis(2,2′-bipyridine)(4-carboxy-4′-(pyrid-2-ylmethylamido)-2,2′-bipyridine)ruthenium(II) di(hexafluorophosphate): Comparison of spectroelectrochemical properties with related complexes

The new complex, [Ru^II(bpy)₂(4-HCOO-4′-pyCH₂ NHCO-bpy)](PF₆)₂ · 3H₂O (1), where 4-HCOO-4′-pyCH₂NHCO-bpy is 4-(carboxylic acid)-4′-pyrid-2-ylmethylamido-2,2′-bipyridine, has been synthesised from [Ru(bpy)₂(H₂dcbpy)](PF₆)₂ (H₂dcbpy is 4,4′-(dicarboxylic acid)-2,2′-bipyridine) and characterised by elemental analysis and spectroscopic methods. An X-ray crystal structure determination of the trihydrate of the [Ru(bpy)₂(H₂dcbpy)](PF₆)₂ precursor is reported, since it represented a different solvate to an existing structure. The structure shows a distorted octahedral arrangement of the ligands around the ruthenium(II) centre and is consistent with the carboxyl groups being protonated. A comparative study of the electrochemical and photophysical properties of [Ru^II(bpy)₂(4-HCOO-4′-pyCH₂NHCO-bpy)]²⁺ (1), [Ru(bpy)₂(H₂dcbpy)]²⁺ (2), [Ru(bpy)₃]²⁺ (3), [Ru(bpy)₂Cl₂] (4) and [Ru(bpy)₂Cl₂]⁺ (5) was then undertaken to determine their variation upon changing the ligands occupying two of the six ruthenium(II) coordination sites. The ruthenium(II) complexes exhibit intense ligand centred (LC) transition bands in the UV region, and broad MLCT bands in the visible region. The ruthenium(III) complex, 5, displayed overlapping LC bands in the UV region and a LMCT band in the visible. 1, 2 and 3 were found, via cyclic voltammetry at a glassy carbon electrode, to exhibit very positive reversible formal potentials of 996, 992 and 893 mV (versus Fc/Fc⁺) respectively for the Ru(III)/Ru(II) half-cell reaction. As expected the reversible potential derived from oxidation of 4 (−77 mV (versus Fc/Fc⁺)) was in excellent agreement with that found via reduction of 5 (−84 mV (versus Fc/Fc⁺)). Spectroelectrochemical experiments in an optically transparent thin-layer electrochemical cell configuration allowed UV-Vis spectra of the Ru(III) redox state to be obtained for 1, 2, 3 and 4 and also confirmed that 5 was the product of oxidative bulk electrolysis of 4. These spectrochemical measurements also confirmed that the oxidation of all Ru(II) complexes and reduction of the corresponding Ru(III) complex are fully reversible in both the chemical and electrochemical senses.     

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.     

New ruthenium(II) precursors with the tetradentate sulfur macrocycles tetrathiacyclododecane ([12]aneS4) and tetrathiacyclohexadecane ([16]aneS4) for the construction of metal-mediated supramolecular assemblies

The preparation and structural characterization of several new Ru(II) complexes in which four coordination positions are occupied by the sulfur atoms of a macrocycle, either 1,4,7,10-tetrathiacyclododecane ([12]aneS4) or 1,5,9,13-tetrathiacyclohexadecane ([16]aneS4), and the two others by relatively labile ligands (Cl⁻, , H₂O, dmso-S), are described:cis-[Ru([12]aneS4)(dmso-S)(H₂O)](CF₃SO₃)₂ (2a), cis-[Ru([12]aneS4)(dmso-S)(ONO₂)](NO₃) (2b), cis-[Ru([16]aneS4)Cl₂] (4), and trans-[Ru([16]aneS4)(dmso-S)(H₂O)](CF₃SO₃)₂ (5).The complexes of the larger [16]aneS4 macrocycle have a flexible coordination geometry, either cis or trans, that makes them unsuited for being used as precursors in metal-driven self-assembly processes.On the contrary, the [12]aneS4 complexes cis-[Ru([12]aneS4)(dmso-S)Cl]Cl (1) and, above all, its chlorido free derivatives cis-[Ru([12]aneS4)(dmso-S)(H₂O)](CF₃SO₃)₂ (2a) and cis-[Ru([12]aneS4)(dmso-S)(ONO₂)](NO₃) (2b) are potential precursors of the geometrically stable 90° bis-acceptor fragment cis-[Ru([12]aneS4)]²⁺.Preliminary results of their reactivity towards the linear linker pyrazine (pyz) showed that the nature of the isolated product depends on that of the counter-anion.When treated with pyz 2b afforded the dinuclear complex [{Ru([12]aneS4)(ONO₂)}₂(μ-pyz)](NO₃)₂ (8), while 2a gave the molecular triangle [{cis-Ru([12]aneS4)(μ-pyz)}₃](CF₃SO₃)₆ (9), both in low yields.The X-ray structures of compounds 2a, 2b, 4, 5, [{Ru([12]aneS4)Cl}₂(μ-pyz)]Cl₂ (7), 9, and of the sandwich complex[Ru([12]aneS3-S)₂](CF₃SO₃)₂ (3), in which only three sulfur atoms of each macrocycle are bound to ruthenium, are also described.     

A hemiacetalate complex of Ru(II)

Reaction of cis-Ru(bisox)₂Cl₂, where bisox is 4,4,4′,4′-tetramethyl-2,2′-bisoxazoline, with excess of pyridine-2-carboxaldehyde (py-2-al) in 1:1 (v/v) methanol-water mixture under nitrogen atmosphere and subsequent addition of excess of NH₄PF₆ give [Ru(bisox)₂(py-2-al)](PF₆)₂ · H₂O (1). Refluxing of 1 in dehydrated methanol in presence of triethylamine yields the corresponding hemiacetalate complex: [Ru(bisox)₂ (pyridine-2-(α-methoxymethanolato))]PF₆ · 1.5H₂O (2). Both the complexes have been characterised by single crystal X-ray crystallography, FTIR and NMR. In cyclic voltammetry in acetonitrile at a glassy carbon electrode, 2 displays a quasireversible Ru(II/III) couple at 1.08 V versus NHE which is not observed in 1. A tentative mechanism is proposed for the conversion of 1 to 2. DFT calculations with the LanL2DZ basis set have been performed to investigate these observations theoretically.     

Structures, magnetic and thermal properties of polynuclear complexes built by pyridine-2,6-dicarboxylic acid-based multi-dentate ligand

By the reactions of a new ligand, 2,6-di(N,N′-5-ethyl-1,3,4-thia-diazole-2-formamide)pyridine (H₂L), with Mn(II) and Cu(II) ions, two complexes namely [Mn₃(μ₃-O)(H₂L)(L)₂]·2DMF (1) and [Cu₂(μ-H₂O)(L)₂]·DMF (2) were obtained, respectively. Compound 1 is a trinuclear complex containing triangle frames formed by three Mn(II) ions with a bridged μ₃-O in the center; ligand H₂L acts as a penta-dentate fashion. Compound 2 is a dinuclear complex, in which H₂L coordinates two Cu(II) centers as a tetra-dentate coordination mode. Magnetic investigations show that an antiferromagnetic coupling between metal ions exists in 1, and a ferromagnetic coupling exists in 2. Thermal decomposition kinetic parameters of complex 1 are also obtained by employing non-isothermal (model-free) method.     

Synthesis and characterization of Ru(arene) complexes of bispyrazolylazines: Catalytic hydrogen transfer of ketones

The bis(pyrazol-1-yl)azine ligands 2,3-bis(pyrazol-1-yl)quinoxaline (bpzqnx), 2,3-bis(pyrazol-1-yl)pyrazine (bpzprz) and 3,6-bis(3,5-dimethylpyrazol-1-yl)pyridazine (bpz*pdz) were prepared by the reaction of pyrazolate salts and the corresponding azine dichloride derivatives. The reaction of these ligands with Ru(arene) precursors led to the mononuclear complexes [RuCl(arene)(L)]BPh₄ (arene = p-cymene, L = bpzqnx, 1, bpzprz, 5, bpz*pdz, 7; arene = C₆H₆, L = bpzqnx, 2, bpzprz, 6, bpz*pdz, 8) with the N-donor ligand coordinated in a bidentate chelate way. In general, the ligands coordinate through one pyrazole ring and the azine, except in the cases of 1 and 2 where the two pyrazolyl rings are coordinated to the metal in a symmetrical way. When the reactions between the ruthenium precursors and bpzqnx are carried out in MeOH, the complexes [RuCl(arene)(OMepzqnx)]BPh₄ with partially methanolyzed ligands are isolated (arene = p-cymene, 3; C₆H₆, 4). In this process a methoxy group has replaced one of the pyrazole groups in the ligand. The X-ray structures of 6 and 7 have been determined. These compounds have a three-legged piano-stool structure with cations and anions packed through weak interactions. Complexes 1-8 are active in ketone hydrogenation transfer processes even in the absence of base.     

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.     

Relative stability of half-sandwich η-benzene Ru(II) complexes of tridentate (2-pyridyl)alkylamine ligands of varying chelate ring-size: Nucleophilic addition of hydride ion onto the benzene ring

A full account of half-sandwich complexes of ruthenium(II) having three-legged “piano-stool” geometry supported by tridentate (2-pyridyl)alkylamine ligands is presented. Reaction of the dimer [{(η⁶-C₆H₆)RuCl(μ-Cl)}₂] with N-methyl-N,N-bis(2-pyridylmethyl)amine (MeL^∗) in CH₃OH in the presence of NH₄PF₆ affords the complex [(η⁶-C₆H₆)Ru(MeL^∗)][PF₆]₂ (1). A similar reaction with N-methyl-N,N-bis(2-pyridylethyl)amine (MeL^∗∗), however, affords a non-organometallic Ru(III)-dimeric complex (5) (the composition of this complex has been established by physicochemical method). Nucleophilic addition reaction on 1 with NaBH₄ leads to the isolation of a cyclohexadienyl complex [(η⁵-C₆H₇)Ru(MeL^∗)][PF₆] (3). The molecular structure of 1 · 2CH₃CN, 3, and previously reported cyclohexadienyl complex [(η⁵-C₆H₇)Ru(MeL)][PF₆] (4) [MeL = N-methyl-[(2-pyridyl)ethyl(2-pyridyl)-methyl]amine], obtained from the reaction between NaBH₄ and previously reported “piano-stool” complex [(η⁶-C₆H₆)Ru(MeL)][PF₆]₂ (2), has been confirmed by X-ray crystallography. Solution-state structure of new complexes 1 and 3 has been elucidated by their ¹H NMR spectra in CD₃CN. The behavior of complex 3 has been investigated with the aid of two-dimensional ¹H NMR spectroscopy, as well. An attempt has been made to provide a rationale for the effect of supporting tridentate N-donor ligand [MeL, MeL^∗, and MeL^∗∗], varying in the chelate ring-size on (i) the relative stability of half-sandwich η⁶-benzene Ru(II) complexes and (ii) the electrophilicity of Ru(II)-coordinated benzene ring on the nucleophilic addition reactions.     

Syntheses, spectroscopies and structures of zinc complexes with malate

Reactions of zinc(II) ion with racemic malic acid (C₄H₆O₅ = H₃mal) result in the isolation of four new zinc(II) malato complexes: (NH₄)[Zn(R-H₂mal)₃] · H₂O (1), trans-[Zn(R-H₂mal)(S-H₂mal)(H₂O)₂] · 2H₂O (2), (NH₄)₂[Zn(R-Hmal)(S-Hmal)] · 2H₂O (3), and [Zn₂(R-Hmal)(S-Hmal)(H₂O)₄]_n · 2nH₂O (4). Three R-malic acids in 1 act as bidentate ligands via their alcoholic and the central carboxy groups with Zn(II) ion, leaving the terminal carboxylic acid groups free. The R- and S-malates of 2 coordinate in a bidentate manner with zinc ion in trans-form. In 3, Zn(II) ion is coordinated by R- and S-malates in a tridentate fashion via their alcoholic and two carboxy groups. Complex 4 forms a two-dimensional layered structure through the links of a new dimeric unit [Zn₂(R-Hmal)(S-Hmal)(H₂O)₄] with one of the oxygen atoms from the terminal carboxy group of malate ligand. The coordination of malates depends on pH variation, on Zn:malate ratio, and also on temperature. Tridentate chelation of malate in 3 is found between pH 4.5-9.0. The soluble monomeric species 1-3 have been investigated using ¹³C NMR spectra by long-time acquisition. The solution NMR spectra indicate that zinc malate complexes dissociate in H₂O (D₂O). Obvious downfield shifts of the central carboxy carbon atoms in 1-3 are observed compared with those of free malate, which indicate that these zinc malate complexes dissociate in aqueous solution.     

sp C-H and sp C-H agostic ruthenium complexes: a combined experimental and theoretical study

Halide abstraction from the 18 electron Ru(II) complex RuCl(CO)₂[2,6-(CH₂P^tBu₂)₂C₆H₃] (2) with AgPF₆ results in the exclusive formation of the cationic complex {Ru(CO)₂[2,6-(CH₂P^tBu₂)₂C₆H₃]}⁺PF₆⁻ (3). The molecular structures of 2 and 3 were determined by complete single-crystal diffraction studies. X-ray crystallographic analysis of 3 reveals that the “open” coordination site is occupied by an agostic interaction between the metal center and an sp³ C-H bond of a tert-butyl substituent. DFT gas phase calculations (B97-1/SDD) show the necessity of two sterically demanding tert-butyl substituents on one P donor atom for the agostic interaction to occur. The reaction of 3 with H₂ results in the quantitative conversion to {Ru(H)(CO)₂[2,6-(CH₂P^tBu₂)₂C₆H₄]}⁺PF₆⁻ (4) where the aromatic C_ipso-H bond is η²-coordinated to the metal center. Treatment of the agostic complex 4 with Et₃N results in the formation of the neutral complex Ru(H)(CO)₂[2,6-(CH₂P^tBu₂)₂C₆H₃] (5). The mechanistic details of 3 + H₂ → 4 were investigated by DFT calculations at the B97-1/SDB-cc-pVDZ//B97-1/SDD level of theory.