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.     

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.     

Luminescent probes for indole-binding proteins derived from ruthenium(II) polypyridine complexes

We report here the synthesis, characterisation, electrochemical, photophysical and protein-binding properties of four luminescent ruthenium(II) polypyridine indole complexes [Ru(bpy)₂(L1)](PF₆)₂ (1), [Ru(bpy)₂(L2)](PF₆)₂ (2), [Ru(L1)₃](PF₆)₂ (1a), and [Ru(L2)₃](PF₆)₂ (2a) (bpy = 2,2′-bipyridine; L1 = 4-(N-(2-indol-3-ylethyl)amido)-4′-methyl-2,2′-bipyridine; L2 = 4-(N-(6-N-(2-indol-3-ylethyl)hexanamidyl)amido)-4′-methyl-2,2′-bipyridine). Their indole-free counterparts, [Ru(bpy)₂(L3)](PF₆)₂ (3) and [Ru(L3)₃](PF₆)₂ (3a) (L3 = 4-(N-(ethyl)amido)-4′-methyl-2,2′-bipyridine), have also been synthesised for comparison purposes. Cyclic voltammetric studies revealed ruthenium-based oxidation at ca. +1.3 V versus SCE and diimine-based reductions at ca. −1.20 to −2.28 V. The indole moieties of complexes 1, 2, 1a and 2a displayed an irreversible wave at ca. +1.1 V versus SCE. All the ruthenium(II) complexes exhibited intense and long-lived orange-red triplet metal-to-ligand charge-transfer ³MLCT (dπ(Ru) → π*(L1-L3)) luminescence upon visible-light irradiation in fluid solutions at 298 K and in alcohol glass at 77 K. The binding of the indole-containing complexes to bovine serum album (BSA) has been studied by quenching experiments and emission titrations.     

Communication of metal ions in the dinuclear ruthenium complexes containing 4,4′-bipyridine, 1,4-diisocyanobenzene, and pyrazine bridging ligands: Synthesis, characterization and structure determination

Reaction of [Ru(2,2′-bipyridine)(2,2′:6′,2″-terpyridine)Cl]PF₆ (abbreviated to [Ru(bipy)(terpy)Cl]PF₆) with 0.5 equiv of the bidentate ligand L produces the dinuclear complexes [{Ru(bipy)(terpy)}₂(μ-L)](PF₆)₄ (L = 4,4′-bipyridine 1, 1,4-diisocyanobenzene 2 and pyrazine 3) in moderate yields. Treating [Ru(bipy)(terpy)Cl]PF₆ with equal molar of 1,4-diisocyanobenzene affords [Ru(bipy)(terpy)(CNC₆H₄NC)](PF₆)₂ (2a). These new complexes have been characterized by mass, NMR, and UV-Vis spectroscopy, and the structures of 1-3 determined by an X-ray diffraction study. Cyclic voltammetric studies suggest that metal communication between the two ruthenium ions increases from 1 to 2 to 3.     

Synthesis and characterization of ruthenium(II) complexes bearing the bis(2-pyridylmethyl)amine ligand

The reaction of [Ru(CO)₂Cl₂]_n with bis(2-pyridylmethyl)amine (bpma) in refluxing ethanol followed by anion exchange yields two products: cis,fac-[Ru(bpma)(CO)₂Cl]PF₆ (1a, 71%) and trans,fac-[Ru(bpma)(CO)₂Cl]PF₆ (1b, 29%). Reaction of 1a with AgBF₄ in acetone, followed by acetonitrile and then anion exchange gave cis,fac-[Ru(bpma)(CO)₂(CH₃CN)](PF₆)₂ (2a). In the same way, 1b afforded trans,fac-[Ru(bpma)(CO)₂(CH₃CN)](PF₆)₂ (2b). Reaction of depolymerized [Ru(CO)₂Cl₂]_n with bpma in ethanol at room temperature afforded cis,cis-[Ru(η²-bpma)(CO)₂Cl₂] (3). In refluxing ethanol, 3 was converted to cis,fac-[Ru(bpma)(CO)₂Cl]Cl (1a-Cl). Heating 3 in chlorobenzene afforded 1b-Cl, exclusively; heating 3 in ethylene glycol gave mainly 1a-Cl. Heating 1a-Cl in ethanol resulted in no isomerization, but heating in chlorobenzene gave a mixture of 3 and 1b-Cl. Anion exchange for PF₆ with 1a-Cl and 1b-Cl afforded 1a and 1b, respectively, whereas anion exchange for BPh₄ afforded 1a-BPh₄. Compounds 1a, 1b, 2a and 3 have been structurally characterized.     

Unusual phenomenon in the chemistry of orthometalated ruthenium (II) complexes

Yellow cyclometalatated ruthenium (II) complexes [Ru(o-X-2-py)(MeCN)₄]PF₆ (1, X = C₆H₄ (a) or 4-MeC₆H₃ (b)) react readily with 1,10-phenanthroline (LL) in MeCN to give brownish-red species cis-[Ru(o-X-2-py)(LL)(MeCN)₂]PF₆ in high yields. The same reaction of the same complexes under the same conditions with 2,2′-bipyridine results in a significant color change from yellow to brownish-orange suggesting a formation of new species. Surprisingly, X-ray structural studies of these two complexes showed that they are structurally indistinguishable from the starting complexes 1. Referred to as complexes 4a,b, the new compounds are slightly more stable in the air though their spectral characteristics in solution are similar to 1a,b. The diffuse reflectance spectroscopy is so far the only technique that indicated differences between 1 and 4.     

Acid dissociation of 2,2′-dipyridylamine in non-aqueous medium when chelated to some Ru(II)N4 cores

[Ru(2,2′-bipyridine)₂(Hdpa)](BF₄)₂ · 2H₂O (1), [Ru(1,10-phenanthroline)₂(Hdpa)] (PF₆)₂ · CH₂Cl₂ (2) and [Ru(4,4,4′,4′-tetramethyl-2,2′- bisoxazoline)₂(Hdpa)] (PF₆)₂ (3) are synthesized where Hdpa is 2,2′-dipyridylamine. The X-ray crystal structures of 1 and 2 have been determined. Hdpa in 1 and 2 is found to bind the metal via the two pyridyl N ends. Comparing the NMR spectra in DMSO-d₆, it is concluded that 3 has a similar structure. The pK_a values (for the dissociation of the NH proton in Hdpa) of free Hdpa and its complexes are determined in acetonitrile by exploiting molar conductance. These correlate linearly with the chemical shift of the NH proton in the respective entities.     

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.     

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.     

Synthesis, photoluminescence and electrochemiluminescence of ruthenium(II) polypyridyl complexes based on bipyridine derivatives with carbazole moieties

Six complexes (1-6) with the type of [Ru(bpy)₂L]X₂ (1-3: L = L1-L3, X = Cl⁻; 4-6: L = L1-L3, X = PF₆⁻) were synthesized based on 2,2′-bipyridine and three 2,2′-bipyridine derivatives L1, L2 and L3 (L1 = 5,5′-dibromo-2,2′-bipyridine, L2 = 5-bromo-5′-carbazolyl-2,2′-bipyridine, L3 = 5,5′-dicarbazolyl-2,2′-bipyridine). The complexes 1-6 were characterized by ¹H NMR, MS(ESI) and IR spectra, along with the X-ray crystal structure analysis for 1, 5 and 6. Their photophysical properties and electrochemiluminescence (ECL) properties were investigated in detail. In the UV-Vis absorption spectra, all complexes 1-6 show strong intraligand (π → π^∗) transitions and metal-ligand charge transfer (MLCT, dπ (Ru) → π^∗) bands. Upon the excitation wavelengths at ∼508 nm, all complexes 1-6 exhibit typical MLCT emission of ruthenium(II) polypyridyl complexes. The introduction of carbazole moieties improves the MLCT absorption and emission intensity. The ruthenium(II) complexes 1-6 exhibit good electrochemiluminescence (ECL) properties in [Ru(bpy)₂L]²⁺/tri-n-propylamine (TPrA) acetonitrile solution and the complexes with PF₆⁻ showed higher ECL emission intensity than that of the complexes with Cl⁻ based on the same ligands.     

Synthesis, structure and spectroscopic properties of 2,3-bis(diphenylphosphino)quinoxaline (dppQx) and its copper(I) complexes

Phosphinoquinoxalines were prepared by treatment of 2,3-dichloroquinoxaline (3) with phosphorus nucleophiles. The Arbuzov reaction of 3 with PPh(O-i-Pr)₂ gave a mixture of diastereomers of 2,3-(PPh(O)(O-i-Pr))₂quinoxaline (6); the crystal structure of rac-6 was determined, but attempts at reduction to yield bis(phenylphosphino)quinoxaline 7 resulted in P-C cleavage and formation of phenylphosphine. The bis(secondary phosphine) 7 could be generated from 3 and LiPHPh(BH₃), but was not isolated in pure form. Copper-catalyzed coupling of PHPh₂ with 3 gave 2,3-bis(diphenylphosphino)quinoxaline (4, dppQx), whose coordination chemistry was investigated, with comparison to data for the analogous 1,2-bis(diphenylphosphino)benzene (dppBz) complexes. Reaction of dppQx with [Cu(NCMe)₄][PF₆] gave [Cu(dppQx)₂][PF₆] (8); CuCl yielded [Cu(dppQx)Cl]₂ (9). Reaction of [Cu(NCMe)₄][PF₆] with one equiv of DPEphos, followed by one equiv of dppQx, gave [Cu(dppQx)(DPEphos)][PF₆] (10). Ligand 4 and copper complexes 8 and 9 were crystallographically characterized. The UV-Vis spectra of dppQx and its copper complexes were red-shifted from those of the dppBz analogs; in contrast to results for the dppBz complexes, those of dppQx were not luminescent in solution.     

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.     

Photophysics of ruthenium(II) complexes carrying amino acids in the ligand 2,2′-bipyridine and intramolecular electron transfer from methionine to photogenerated Ru(III)

New ruthenium(II) complexes carrying methionine and phenylalanine in the bipyridine ligand, [Ru(bpy)₂(4-Me-4′-(CONH-l-methionine methyl ester)-2,2′-bipyridine)](PF₆)₂ (IV) and [Ru(bpy)₂(4-Me-4′-(CONH-l-phenylalanine ethyl ester)-2,2′-bpy)](PF₆)₂(V) have been synthesized and characterized and their photophysical properties studied. Flash photolysis measurements of complex IV, in the presence of an electron acceptor, methyl viologen (MV²⁺) show that an intermolecular electron transfer from the excited state of Ru(II) in complex IV, to MV²⁺ takes place, forming Ru(III) and the methyl viologen cation radical, MV⁺. The formation of MV⁺ in this system is confirmed using time-resolved transient absorption spectroscopy. This intermolecular electron transfer is followed by intramolecular electron transfer from the thioether moiety (methionine) to the photogenerated Ru(III), regenerating Ru(II).     

Arene-Ru(II)-chloroquine complexes interact with DNA, induce apoptosis on human lymphoid cell lines and display low toxicity to normal mammalian cells

The complexes [Ru(η⁶-p-cymene)(CQ)Cl₂] (1), [Ru(η⁶-benzene)(CQ)Cl₂] (2), [Ru(η⁶-p-cymene)(CQ)(H₂O)₂][BF₄]₂ (3), [Ru(η⁶-p-cymene)(en)(CQ)][PF₆]₂ (4), [Ru(η⁶-p-cymene)(η⁶-CQDP)][BF₄]₂ (5) (CQ = chloroquine base; CQDP = chloroquine diphosphate; en = ethylenediamine) interact with DNA to a comparable extent to that of CQ and in analogous intercalative manner with no evidence for any direct contribution of the metal, as shown by spectrophotometric and fluorimetric titrations, thermal denaturation measurements, circular dichroism spectroscopy and electrophoresis mobility shift assays. Complexes 1-5 induced cytotoxicity in Jurkat and SUP-T1 cancer cells primarily via apoptosis. Despite the similarities in the DNA binding behavior of complexes 1-5 with those of CQ the antitumor properties of the metal drugs do not correlate with those of CQ, indicating that DNA is not the principal target in the mechanism of cytotoxicity of these compounds. Importantly, the Ru-CQ complexes are generally less toxic toward normal mouse splenocytes and human foreskin fibroblast cells than the standard antimalarial drug CQDP and therefore this type of compound shows promise for drug development.     

Synthesis and single crystal structures of first examples of tridentate ligands of (Te, N, S) type and their complexes with palladium(II), platinum(II) and ruthenium(II)

The First examples of (Te, N, S) type ligands, 2-CH₃SC₆H₄CHNCH₂CH₂TeC₆H₄-4-OCH₃ (L¹) and 2- CH₃SC₆H₄CHNHCH₂CH₂TeC₆H₄-4-OCH₃ (L²), and their metal complexes, [PdCl(L¹)]PF₆ · CHCl₃ · 0.5H₂O (4), [PtCl(L¹)]PF₆ (5), [PdCl(L²)]ClO₄.CHCl₃ (6), [PtCl(L²)]ClO₄ (7), and [Ru(p-cymene)(L²)](PF₆)₂ · CHCl₃ (8), have been synthesized and characterized. The single crystal structures of 4, 6 and 8 have revealed that both the ligands coordinate in them in a tridentate (Te, N, S) mode. The geometry around Pd in both the complexes has been found to be square planar, whereas for Ru in a half sandwich complex 8, it is found to be octahedral. Between two molecules of 4 there are intra and inter molecular weak Te?Cl [3.334(3) and 3.500(3) Å, respectively] interactions along with weak intermolecular Pd?Te [3.621(2) Å] interactions. The Pd-Te bond lengths are between 2.517(6) and 2.541(25) Å and the Ru-Te bond length is 2.630(6) Å. The crystal structure of [PdCl₂(4-MeO-C₆H₄- TeCH₂CH₂NH₂)] (9) is also determined. It is formed when KPF₆ is not added in the synthesis of 4 and Pd-complex of L¹ is recrystallized. Apart from Te?Cl secondary interactions, C-H?π interactions also exist in the crystal of 9.     

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.     

Synthesis and characterization of the cobalt(III) complexes of two pendant-arm cross-bridged cyclams

The cobalt(III) complexes of 4,11-diacetato-1,4,8,11-tetraazabicyclo[6.6.2]hexadecane (1), [Co(1)]PF₆, and 4,11-diacetamido-1,4,8,11-tetraazabicyclo[6.6.2]hexadecane (2), [Co(2)][PF₆]₃, have been synthesized and characterized. The crystal structure of [Co(1)]PF₆ consists of an octahedral cobalt(III) cation coordinated to all four ligand nitrogen donors in the macrobicycle’s cavity, as well as to the deprotonated carboxylate oxygen atoms of both pendant arms. Analytical and spectroscopic data indicates that the ligand in [Co(2)][PF₆]₃ is not deprotonated, suggesting coordination through the amide carbonyl oxygens. Study of the electronic spectra of these novel complexes and comparison with data from related cobalt(III) complexes characterizes the ligands as strong field with Δ₀=24,040 and Δ₀=24,250 cm⁻¹ for 1 and 2, respectively. Cyclic voltammograms were obtained for both complexes with large variations observed due to the differences in ligand charge and coordination.     

Unsymmetric diruthenium complexes

The new diruthenium complexes trans-[(NH₃)₅Ru(L-L)Ru(NH₃)₄(bpy-Me)](PF₆)₅ (L-L are the bridging ligands pyrazine, 2a; 4,4′dipyridyl, 2b; and trans-1,2-bis(4-pyridyl)-ethylene, 2c; bpy-Me is N-methyl-pyridyl-pyridinium) are generated from the new complexes (L-L)Ru(NH₃)₄(bpy-Me)](PF₆)₃ (1a-c) and [(NH₃)₅Ru(H₂O)](PF₆)₂. Cyclic voltammetry on the new compounds in acetonitrile electrolyte reveals two quasi-reversible oxidation steps corresponding to the two Ru^II/III couples in 2b and 2c and a single oxidations for 1a-c. In addition, two reduction waves are observed for the bpy-Me ligands of 1a-c and 2a-c. All of the new compounds exhibit multiple metal-to-ligand charge transfer (MLCT) bands in the visible region of the spectrum. For compounds 1a-c the most intense absorption in the visible region decreases in energy as the length of the aromatic bridging ligands increases. By contrast the strongest absorption band of 2a is lower in energy than the most intense bands of both 2b and 2c. Single crystal X-ray analysis of 2a reveals that the bridging pyridine is coplanar with the pyridyl ring of the bpy-Me ligand that is attached to the Ru center. DFT calculations on 2a indicate that the HOMO is localized predominately on the {(NH₃)₅Ru-pyz-Ru(NH₃)₄} portion of the complex and the LUMO has slightly more contribution from the bpy-Me ligand.     

Protonated 4′-(2-pyridyl)-2,2′:6′,2″-terpyridine and its Fe(II) bischelates: Syntheses and molecular structures

Compounds of the molecular formulae, [LH₃](NO₃)₃ (1), [Fe(LH)₂](PF₆)₄·5H₂O (2), [Fe(L)₂][Fe(L)(LH)](PF₆)₅·H₂O (3), [Fe(L)₂][Fe(L)(LH)](BF₄)₅·2H₂O (4) and [Fe(L)₂](Cr₂O₇)·6H₂O (5) have been synthesized using 4′-(2-pyridyl)-2,2′:6′,2″-terpyridine (L). The molecular structures of all the compounds were determined. The Fe(II) complexes are high spin in nature at room temperature and upon cooling a gradual spin-transition is observed. Among 1-5, hydrogen-bonding, π···π, and anion···π interactions as well as water tetramer and pentamer are present in the molecular packing.     

Homo- and heteronuclear complexes based on arene ruthenium complexes bearing bis(diphenylphosphinomethyl)phenylphosphine (dpmp)

Reactions of [(p-cymene)RuCl₂]₂ (1a) with dpmp ((Ph₂PCH₂)₂PPh) in the absence or presence of KPF₆ afforded the ionic complexes [{(p-cymene)RuCl₂}(dpmp-P¹,P³;P²){RuCl(p-cymene)}](X) (2a₁: X=Cl; 2a₂: X=PF₆). A (p-cymene)RuCl moiety constructs a 6-membered ring coordinated by two terminal P atoms of the dpmp ligand and another one binds to a central P atom of the ligand. Reactions of [(C₆Me₆)RuCl₂]₂ (1b) with an excess of dpmp in the presence of KPF₆ gave a 4-membered complex [(C₆Me₆)RuCl(dpmp-P¹,P²)](PF₆) (3b), chelated by a terminal and a central P atom and another terminal atom is free. Use of Ag(OTf) instead of KPF₆ gave [{(C₆Me₆)RuCl₂(dpmp)Ag} ₂](OTf)₂ (5b) that the Ag atoms were coordinated by a terminal and a central P atom of each dpmp ligand. Reaction with an equivalent of dpmp in the presence of KPF₆ gave [{(C₆Me₆)RuCl}(dpmp-P¹,P²;P³){(C₆Me₆)RuCl₂}](PF₆) 4b. Complex has a structure that the (C₆Me₆)RuCl₂ moiety coordinated to the free P atom of 3b. Complex 3b was treated with MCl₂(cod) (M=Pd, Pt), [Pd(MesNC)₄](PF₆)₂ (MesNC=2,4,6-Me₃C₆H₂NC) or [Pt₂(XylNC)₆](PF₆)₂ (XylNC=2,6-Me₂C₆H₃NC), generating [{(C₆Me₆)RuCl(dpmp)}₂MCl₂](PF₆)₂ (8b: M=Pd; 9b: M=Pt), [{(C₆Me₆)RuCl(dpmp)}₂{Pt(MesNC)₂}](PF₆)₄ (10b) and [{(C₆Me₆)RuCl(dpmp)}₂{Pt₂(XylNC)₄}](PF₆)₄ (11b), respectively. Complex 3b reacted readily with [Cp*MCl₂]₂ (M=Rh, Ir) or AuCl(SC₄H₈), affording the corresponding hetero-binuclear complexes [{(C₆Me₆)RuCl}(dpmp-P¹,P²;P³)(MCl₂Cp^*](PF₆) (6b: M=Rh; 7b: M=Ir) and [{(C₆Me₆)RuCl}(dpmp-P¹,P²;P³)(AuCl)](PF₆) (12b). These complexes have two chiral centers. Some complexes were separated as two diastereomers by successive recrystallization. The structures of 3b, 5b, 6b, 8b and 12b were confirmed by X-ray analyses.