Paramagnetic Ruthenium Research Articles

Biomolecular Interactions of Cytotoxic Ruthenium Compounds with Thiosemicarbazone or Benzothiazole Schiff Base Chelates.

Herein we illustrate the formation and characterization of new paramagnetic ruthenium compounds, trans-P-[RuCl(PPh3 )2 (pmt)]Cl (1) (Hpmt=1-((pyridin-2-yl)methylene)thiosemicarbazide), trans-P-[RuCl(PPh3 )2 (tmc)]Cl (2) (Htmc=1-((thiophen-2-yl)methylene)thiosemicarbazide) and a diamagnetic ruthenium complex, cis-Cl, trans-P-[RuCl2 (PPh3 )2 (btm)] (3) (btm=2-((5-hydroxypentylimino)methyl)benzothiazole). Agarose gel electrophoresis experiments of the metal compounds illustrated dose-dependent binding to gDNA by 1-3, while methylene blue competition assays suggested that 1 and 2 are also DNA intercalators. Assessment of the effects of the compounds on topoisomerase function indicated that 1-3 are capable of inhibiting topoisomerase I activity in terms of the ability to nick supercoiled plasmid DNA. The cytotoxic activities of the metal complexes were determined against a range of cancer cell lines versus a non-tumorigenic control cell line, and the complexes were, in general, more cytotoxic towards the cancer cells, displaying IC50 values in the low micromolar range. Time-dependent stability studies showed that in the presence of strong nucleophilic species (such as DMSO), the chloride co-ligands of 1-3 are rapidly substituted by the former as proven by the suppression of the substitution reactions in the presence of an excess amount of chloride ions. The metal complexes are significantly stable in both DCM and an aqueous phosphate buffer containing 2 % DMSO.

Synthetic, characterization and cytotoxic studies of ruthenium complexes with Schiff bases encompassing biologically relevant moieties

This research study describes the formation and characterization of novel paramagnetic ruthenium complexes, cis-Cl, trans-P-[RuIIICl2(carboim)(PPh3)2] with bidentate chelating carbohydrazide Schiff bases (carboim = bpc for 1, ttc for 2 and tpc for 3). These metal complexes were synthesized by the equimolar coordination reactions of trans-[RuCl2(PPh3)2] with N-[1,3-benzothiazole-2-ylmethylidene]pyridine-2-carbohydrazide (Hbpc), N-((uracil-5-yl)methylene)thiophene-2-carbohydrazide (Httc) and N-[(uracil-5-yl)methylidene]pyridine-2-carbohydrazide (Htpc), respectively. Physicochemical techniques including nuclear magnetic resonance-, electron-spin resonance- and infrared spectroscopy, UV–Vis spectrophotometry, voltammetry as well as molar conductivity measurements provided definitive determinations of the respective ruthenium compounds’ structures. The DPPH and NO radical scavenging capabilities of 1–3 and two previously reported ruthenium(II) complexes, trans-[RuCl(PPh3)2(Htdp)] (H2tdp = 5-((thiophen-3-yl)methyleneamino)-6-amino-1,3-dimethyluracil) (4) and [RuCl(PPh3)(H3ucp)] (H4ucp = 2,6-bis-((6-amino-1,3-dimethyluracilimino)methylene)pyridine) (5), were investigated. The calf-thymus DNA binding capabilities of 1–5 were explored using electronic spectroscopy and gel electrophoresis. In vitro anticancer studies showed that 1 and 2 were not active in the range tested, while 3–5 were toxic to HCC70 breast carcinoma cells, with 4 showing promising IC50 at 3.4 µM.

Anticancer evaluation of ruthenium(III) complexes with N-donor ligands tethered to coumarin or uracil moieties

In this study, the synthesis and characterization of new paramagnetic ruthenium(III) complexes: cis-[RuCl2(urdpa)] (1) {Hurdpa = 6-((bis(pyridin-2-ylmethyl)amino)methyl)uracil} and fac-[RuCl3(chrdpa)] (2) {chrdpa = 4-((bis(pyridin-2-ylmethyl)amino)methyl)-7-methoxycoumarin} are reported. These metal complexes have been comprehensively characterized by an array of physicochemical techniques and the X-ray solid-state structures of 1 and Hurdpa have been attained. Electronic spectroscopy Calf-Thymus DNA titrations revealed that both 1 and 2 are groove binders while molecular docking calculations indicated that the ligands’ steric factors dictate the mode of interaction of these individual ruthenium(III) species. These mononuclear ruthenium compounds were screened against cervical and breast cancer cell lines and show activity in the high micromolar range.

Through-Space Paramagnetic NMR Effects in Host-Guest Complexes: Potential Ruthenium(III) Metallodrugs with Macrocyclic Carriers.

The potential of paramagnetic ruthenium(III) compounds for use as anticancer metallodrugs has been investigated extensively during the past several decades. However, the means by which these ruthenium compounds are transported and distributed in living bodies remain relatively unexplored. In this work, we prepared several novel ruthenium(III) compounds with the general structure Na+[ trans-RuIIICl4(DMSO)(L)]- (DMSO = dimethyl sulfoxide), where L stands for pyridine or imidazole linked with adamantane, a hydrophobic chemophore. The supramolecular interactions of these compounds with macrocyclic carriers of the cyclodextrin (CD) and cucurbit[ n]uril (CB) families were investigated by NMR spectroscopy, X-ray diffraction analysis, isothermal titration calorimetry, and relativistic DFT methods. The long-range hyperfine NMR effects of the paramagnetic guest on the host macrocycle are related to the distance between them and their relative orientation in the host-guest complex. The CD and CB macrocyclic carriers being studied in this account can be attached to a vector that attracts the drug-carrier system to a specific biological target and our investigation thus introduces a new possibility in the field of targeted delivery of anticancer metallodrugs based on ruthenium(III) compounds.

Ruthenium(II) and Ruthenium(III) Complexes of p-Benziporphyrin: Merging Equatorial and Axial Organometallic Coordination.

A diamagnetic ruthenium(II) complex of 5,10,15,20-tetraphenyl-p-benziporphyrin [RuII(p-BzP)(CO)Cl] was obtained via the insertion of ruthenium into p-benziporphyrin using triruthenium(0) dodecacarbonyl [Ru3(CO)12] as the metal source. The procedure applying dichloro(cycloocta-1,5-diene)ruthenium(II) (polymer, [Ru(COD)Cl2]n) afforded the paramagnetic six-coordinate ruthenium(III) p-benziporphyrin [RuIII(p-BzP)Cl2]. As shown by X-ray crystallography, the p-phenylene ring in both complexes is sharply tilted out of the N3 plane, as reflected by the respective N3 (pyrrole)-C6 (p-phenylene) dihedral angle [RuII(p-BzP)(CO)Cl, 52.5°; RuIII(p-BzP)Cl2, 53.7°]. p-Phenylene is bound to the ruthenium cation in an η2 fashion, revealing the shortest ever Ru-C distance in the series of p-benziporphyrin complexes [RuII(p-BzP)(CO)Cl, 2.275(2) Å; RuIII(p-BzP)Cl2, 2.324(5) Å]. The reaction of RuII(p-BzP)(CO)Cl with ArMgCl or AlkMgCl results in the formation of diamagnetic six-coordinate ruthenium(II) p-benziporphyrin complexes containing the apically coordinated σ-alkyl or σ-aryl ligands, where the metal ion simultaneously coordinates to three carbon centers respectively accommodating η2 (phenylene) and σ (aryl and alkyl) modes. Reactions of σ-aryl (alkyl) carbanions with paramagnetic RuIII(p-BzP)Cl2 have been followed by 1H NMR spectroscopy. The procedure afforded the six-coordinate paramagnetic ruthenium(III) p-benziporphyrin [RuIII(p-BzP)(Ph)Cl], which binds one σ-aryl ligand, as reflected by the characteristic 1H NMR spectra spread within the +120 to -120 ppm range. Both paramagnetic complexes RuIII(p-BzP)(Ph)Cl and RuIII(p-BzP)(p-Tol)Cl are formed as a mixture of two stereoisomers differentiated by two nonequivalent locations of σ-aryl with respect to the puckered macrocyclic ring. The paramagnetic shifts of σ-aryls are indicative of π-spin delocalization patterns. Analysis of the contact shifts and parallel density functional theory calculations of the spin density distribution in RuIII(p-BzP)Cl2, RuIII(p-BzP)(Ar)Cl, and RuIII(p-BzP)(Alk)Cl reflect the features of the dxy2(dxzdyz)3 electronic ground state.

Formation, electrochemical and radical scavenging properties of novel ruthenium compounds with N, X-donor (X = O, N) heterocyclic chelators

Herein, we communicate the formation of novel ruthenium compounds with N, X-donor (X=O, N) heterocyclic-derived ligands. A paramagnetic ruthenium(IV) complex, [RuCl(pho)(bzca)(PPh3)](1) (pho=2-aminophenolate; bzca=2-carboxylate-1H-benzimidazole) was isolated from the reaction of the ruthenium(II) precursor, trans-[RuCl2(PPh3)3] and 2-((1H-benzimidazole)methylamino)phenol (Hbzap). The 1:1 molar reaction between the same metal precursor and N-(benzoxazole)-2-hydroxybenzamide (H2bhb) led to the formation of cis-Cl, trans-P-[RuIII(Hbhb)Cl2(PPh3)2](2). The dinuclear ruthenium compounds, (μ-Htba,Cl)2[RuIICl(PPh3)]2(3) (Htba=N-(thiophene)methyl-benzoxazole-2-amine) and (μ-Cl)2[RuIIICl(Hchpr)(PPh3)]2(4) (H2chpr=2-amino-3-((tetrahydro-2H-pyran-4-ylimino)methyl)-4H-chromen-4-one) were formed from the equimolar ratio coordination reactions between trans-[RuCl2(PPh3)3] and the respective free-ligands, Htba and H2chpr. These metal complexes were characterized via IR-, NMR- and UV–Vis spectroscopy, molar conductivity measurements and structural elucidations were confirmed by single crystal X-ray analysis. The X-ray studies revealed that all the metallic compounds exhibited octahedral geometries and that the Hbzap free ligand has undergone a unique molecular transformation to afford the pho and bzca bidentate chelators in 1. The electrochemical properties of the respective metal complexes were investigated by voltammetric analysis. The cyclic voltammograms (CVs) of 1–3 showed one redox couple while within the CV of the dinuclear compound 4, two redox couples were observed. The ligands and their metal complexes were also subjected to DPPH radical scavenging studies. The IC50 values showed that all the metallic compounds have higher radical scavenging activities than their corresponding free-ligands and the natural antioxidant, Vitamin C.

Isolation of ruthenium compounds with bidentate benz(imidazole/othiazole) chelators

Herein, we report the isolation of ruthenium(II/III) compounds with N,O-donor heterocyclic ligands. The 1:2 molar ratio reactions of trans-[RuCl2(PPh3)3] with 2-hydroxyphenylbenzimidazole (Hobz) and 2-hydroxyphenylbenzothiazole (Hobs), respectively, led to the formation of the diamagnetic ruthenium(II) complex salt, [RuCl(Hobz)2(PPh3)]Cl(1) and the paramagnetic ruthenium complex, [RuIIICl(obs)2(PPh3)](2). The X-ray crystal structures of both metal complexes show a distorted octahedral geometry imposed by the ‘2 + 2’ coordination modes of their chelators. The ruthenium compounds 1 and 2 were also characterized via physico-chemical and spectroscopic methods. In addition, the redox properties were probed using cyclic voltammetry and the presence of the paramagnetic metal centre of compound 2 was confirmed by low and room temperature electronic paramagnetic resonance spectroscopy in the liquid and solid states. Furthermore, density functional theory studies indicated that the complex cation of 1 was more energetically favourable than that of the neutral complex 2.

Ruthenium complexes with Schiff base ligands containing benz(othiazole/imidazole) moieties: Structural, electron spin resonance and electrochemistry studies

Novel ruthenium(II/III) complexes of Schiff bases containing benzimidazole (bz) or benzothiazole (bs) moieties were isolated: the diamagnetic ruthenium complex, cis-[RuIICl2(bzpy)(PPh3)2] (1) was formed from the 1:1M reaction between N-((pyridine-2-yl)methylene)-1H-benzimidazole (bzpy) and metal precursor, trans-[RuCl2(PPh3)3]. The same metal precursor, when reacted with the benzimidazole-derived Schiff bases [N-(2-hydroxybenzylidene)-benzothiazole (Hbsp) and N-(2-hydroxybenzylidene)-benzimidazole (Hbzp)], afforded the paramagnetic ruthenium(III) complexes [RuCl(bsp)2(PPh3)] (2) and trans-[RuCl(bzp)(PPh3)2] (3), respectively. These metal complexes were characterized via IR, mass and UV–Vis spectroscopy, elemental analysis, single crystal XRD analysis as well as conductivity measurements. Their redox properties were probed by voltammetry and accompanying UV–Vis spectroelectrochemistry experiments. Structural features of complex 1 were further investigated by multinuclear (1H and 31P) NMR spectroscopy. The presence of the paramagnetic metal centres of 2 and 3 were confirmed by X-band ESR spectroscopy.

Electronic and molecular behaviors of a novel ionic paramagnetic ruthenium(iii) complex

The geometric structures, electronic and molecular properties of the novel ionic paramagnetic ruthenium(III) complex-bis[1-butyl-2-(diphenylphosphanyl)-3-methylimidazolium]tetrachloridoruthenium(III) hexafluorophosphate, which was synthesized experimentally very recently, are investigated by means of first-principles calculations. The molecular structures consistent with the experiment were obtained by optimized calculations. The detailed analysis of the chemical bonding in the ruthenium(III) complex indicates that the interactions of Ru-Cl and Ru-P are dominated by an ionic interaction, while the P-C bonding is of mainly covalent interaction. Our results also show that the ruthenium(III) complex is of magnetic character with a magnetic moment of 1 μb contributed by the central metal atom-Ru. In addition, identifying the orbital compositions in the frontier electronic structures, we proposed that the high catalytic performance of the Ruthenium(III) complex mainly arises from the strong interaction of the frontier orbitals between the reactants and the catalyst. These findings can contribute to a comprehensive understanding about such types of transition metal complexes and shed insight into the synthesis and application of catalyst precursors for the transfer hydrogenation of ketones.

Chelating properties of permethylated 6A,6D-dideoxy-6A,6D-bis(1-imidazolyl)cyclodextrins towards Pt(II) and Ru(III)

Two imidazole-coordinating groups have been successfully grafted onto the C-6A and C-6D positions of permethylated α- and β-cyclodextrin scaffolds. Both water-soluble ligands L1 and L2 turned out to behave as good chelators when reacted with K2PtCl4. In the resulting diamagnetic cis-chelate complexes, the metal cation is pending above the cavity entrance. Paramagnetic ruthenium(III) chelate complexes have also been successfully synthesised from L1 and L2. In these more sterically demanding octahedral complexes, the imidazole groups coordinate the metal centre in a trans-fashion.

Synthesis of an Ionic Paramagnetic Ruthenium(III) Complex and Its Application as an Efficient and Recyclable Catalyst for the Transfer Hydrogenation of Ketones

AbstractA novel ionic complex, bis[1‐butyl‐2‐(diphenylphosphanyl)‐3‐methylimidazolium]tetrachloridoruthenium(III) hexafluorophosphate (2), has been synthesized and fully characterized. The single‐crystal X‐ray diffraction analysis showed that 2 is composed of an Ru complex cation and PF6– anion. The cation has a highly symmetrical Ru‐centered octahedron geometry with four Cl atoms in the equatorial plane and two imidazolium‐substituted phosphane ligands in the axial positions. It exhibits paramagnetism due to the presence of one unpaired electron in the phosphane‐ligated low‐spin RuIII complex. Complex 2 exhibited good catalytic performance in the transfer hydrogenation of a wide range of ketones by using alcohols as hydrogen donors. Owing to its high polarity, good thermal stability, and insensitivity to moisture and oxygen, complex 2 could be used in six catalytic cycles in the transfer hydrogenation of acetophenone without any obvious loss of activity.

Paramagnetic ruthenium(III) complexes bearing O,O chelating ligands: Synthesis, spectra, molecular structure and electron transfer properties

Paramagnetic Ru(III) complexes of the type [RuX 2(EPh 3) 2(L)] (where X = Cl or Br; E = P or As; L = monobasic bidentate benzophenone ligand) have been synthesized from the reaction of ruthenium(III) precursors, viz. [RuX 3(EPh 3) 3] (where X = Cl, E = P; X = Cl or Br, E = As) or [RuBr 3(PPh 3) 2(CH 3OH)] and substituted hydroxy benzophenones in a 1:1 molar ratio in benzene under reflux for 6 h. The hydroxy benzophenone ligands behave as monoanionic bidentate O,O donors and coordinate to ruthenium through the phenolate oxygen and ketonic oxygen atoms, generating a six-membered chelate ring. The compositions of the complexes have been established by analytical and spectral (FT-IR, UV–Vis, EPR) and X-ray crystallography methods. The single crystal structure of the complex [RuCl 2(PPh 3) 2(L 1)] ( 1) has been determined by X-ray crystallography and indicates the presence of a distorted octahedral geometry in these complexes. The magnetic moment values of the complexes are in the range 1.75–1.89 μ B, which reveals the presence of one unpaired electron in the metal ion. EPR spectra of liquid samples at liquid nitrogen temperature (LNT) show a rhombic distortion ( g x ≠ g y ≠ g z ) around the ruthenium ion. The complexes are redox active and display quasi-reversible oxidation and quasi-reversible reduction waves versus Ag/AgCl.

Insertion reactions of [M(SR)3(PMe2Ph)2] with CS2 (M = Ru, Os; R = C6F4H-4, C6F5). X-ray structures of [Ru(S2CSC6F4H-4)2(PMe2Ph)2], trans-thiolates [M(SR)2(S2CSR)(PMe2Ph)2] (M = Ru; R = C6F5 and M = Os; R = C6F4H-4), and trans-thiolate-phosphine [Os(SC6F5)2(S2CSC6F5)(PMe2Ph)2

Reactions of [M(SR)(3)(PMe(2)Ph)(2)] (M = Ru, Os; R = C(6)F(4)H-4, C(6)F(5)) with CS(2) in acetone afford [Ru(S(2)CSR)(2)(PMe(2)Ph)(2)] (R = C(6)F(4)H-4, 1; C(6)F(5), 3) and trans-thiolates [Ru(SR)(2)(S(2)CSR)(PMe(2)Ph)(2)] (R = C(6)F(4)H-4, 2; C(6)F(5), 4) or the isomers trans-thiolates [Os(SR)(2)(S(2)CSR)(PMe(2)Ph)(2)] (R = C(6)F(4)H-4, 5; C(6)F(5), 7) and trans-thiolate-phosphine [Os(SR)(2)(S(2)CSR)(PMe(2)Ph)(2)] (R = C(6)F(4)H-4, 6; C(6)F(5), 8) through processes involving CS(2) insertion into M-SR bonds. The ruthenium(III) complexes [Ru(SR)(3)(PMe(2)Ph)(2)] react with CS(2) to give the diamagnetic thiolate-thioxanthato ruthenium(II) and the paramagnetic ruthenium(III) complexes while osmium(III) complexes [Os(SR)(3)(PMe(2)Ph)(2)] react to give the paramagnetic thiolate-thioxanthato osmium(III) isomers. The single-crystal X-ray diffraction studies of 1, 4, 5, and 8 show distorted octahedral structures. (31)P [(1)H] and (19)F NMR studies show that the solution structures of 1 and 3 are consistent with the solid-state structure of 1.

2,2′:6′,2″-Terpyridine and bis(2,2′:6′,2″-terpyridine)ruthenium(II) complex on the dendritic periphery

2,2′:6′,2″-Terpyridine end-functionalized dendrimers were prepared utilizing chlorinated siloxane dendrimer and 6-hydroxyhexa-4′-(2,2′:6′,2″-terpyridine) ether. The terpyridine groups on dendrimers accepted the ruthenium chloride ions on the mild condition that produced the paramagnetic ruthenium complex G n- mTPY-RuCl 3. The continual addition of 2,2′:6′,2″-terpyridine to the ruthenium–terpyridine complex on the dendritic periphery progressed to bis(2,2′:6′,2″-terpyridine)ruthenium(II) complex G n- m[TPY-Ru-TPY] ( n=1, m=4; n=2, m=8; n=3, m=16) which revealed diamagnetic property.

First example of mu(3)-sulfido bridged mixed-valent triruthenium complex triangle Ru(III)(2)Ru(II)(O,O-acetylacetonate)(3)(mu-O,O,gamma-C-acetylacetonate)(3)(mu(3)-S) (1) incorporating simultaneous O,O- and gamma-C-bonded bridging acetylacetonate units. Synthesis, crystal structure, and spectral and redox properties.

The reaction of mononuclear ruthenium precursor [Ru(II)(acac)(2)(CH(3)CN)(2)] (acac = acetylacetonate) with the thiouracil ligand (2-thiouracil, H(2)L(1) or 6-methyl -2-thiouracil, H(2)L(2)) in the presence of NEt(3) as base in ethanol solvent afforded a trinuclear triangular complex Ru(3)(O,O-acetylacetonate)(3)(mu-O,O,gamma-C-acetylacetonate)(3)(mu(3)-sulfido) (1). In 1, each ruthenium center is linked to one usual O,O-bonded terminal acetylacetonate molecule whereas the other three acetylacetonate units act as bridging functions: each bridges two adjacent ruthenium ions through the terminal O,O-donor centers at one end and via the gamma-carbon center at the other end. Moreover, there is a mu(3)-sulfido bridging in the center of the complex unit, which essentially resulted via the selective cleavage of the carbon-sulfur bond of the thiouracil ligand. In diamagnetic complex 1, the ruthenium ions are in mixed valent Ru(III)Ru(III)Ru(II) state, where the paramagnetic ruthenium(III) ions are antiferromagnetically coupled. The single crystal X-ray structure of 1 showed two crystallographically independent C(3)-symmetric molecules, Ru(3)(O,O-acetylacetonate)(3)(mu-O,O,gamma-C-acetylacetonate)(3)(mu(3)-S) (1), in the asymmetric unit. Bond distances of both crystallographically independent molecules are almost identical, but there are some significant differences in bond angles (up to 6 degrees ) and interplanar angles (up to 8 degrees ). Each ruthenium atom exhibits a distorted octahedral environment formed by four oxygen atoms, two from each of the terminal and bridging acetylacetonate units, one gamma-carbon of an adjacent acetylacetonate ligand, and the sulfur atom in the center of the complex. In agreement with the expected 3-fold symmetry of the complex molecule, the (1)H and (13)C NMR spectra of 1 in CDCl(3) displayed signals corresponding to two types of ligand units. In dichloromethane solvent, 1 exhibited three metal center based successive quasireversible redox processes, Ru(III)Ru(III)Ru(III)-Ru(III)Ru(III)Ru(II) (couple I, 0.43 V vs SCE); Ru(III)Ru(III)Ru(IV)-Ru(III)Ru(III)Ru(III) (couple II, 1.12 V); and Ru(III)Ru(III)Ru(II)-Ru(III)Ru(II)Ru(II) (couple III, -1.21 V). However, in acetonitrile solvent, in addition to the three described couples [(couple I), 0.34 V; (couple II), 1.0 V; (couple III), -1.0], one irreversible oxidative response (Ru(III)Ru(III)Ru(IV) --> Ru(III)Ru(IV)Ru(IV) or oxidation of the coordinated sulfide center) appeared at E(pa), 1.50 V. The large differences in potentials between the successive couples are indicative of strong coupling between the ruthenium ions in the mixed-valent states. Compound 1 exhibited a moderately strong charge-transfer (CT) transition at 654 nm and multiple ligand based intense transitions in the UV region. In the Ru(III)Ru(III)Ru(III) (1(+)) state, the CT band was slightly blue shifted to 644 nm; however, the CT band was further blue shifted to 520 nm on two-electron oxidation to the Ru(III)Ru(III)Ru(IV) (1(2+)) state with a reduction in intensity.

New paramagnetic ruthenium complexes via one-electron reduction of metallacumulenes

One-electron reductions of [Cl(dppe)2RuCCCR2]PF6 (R = Ph, Me) and [Cl(dppe)2RuCCCCCPh 2]PF6 with Co(C5H5)2 provide radical species with the unpaired electron localized on the trisubstituted carbon atom of the cumulene moiety as shown by hydrogen atom capture and EPR spectroscopy.

Ruthenium(II/III) bipyridine complexes incorporating thiol-based imine functions: Synthesis, spectroscopic and redox properties

A group of five new ruthenium(II) bipyridine heterochelates of the type [Ru II(bpy) 2L] + 1a– 1e have been synthesized (bpy=2,2′-bipyridine; L=anionic form of the thiol-based imine ligands, HS–C 6H 4NC(H)C 6H 4(R) (R=OMe, Me, H, Cl, NO 2). The complexes 1a− 1e are 1:1 conducting and diamagnetic. The complexes 1a− 1e exhibit strong MLCT transitions in the visible region and intra-ligand transitions in the UV region. In acetonitrile solvent complexes show a reversible ruthenium(III)–ruthenium(II) couple in the range 0.2–0.4 V and irreversible ruthenium(III)→ruthenium(IV) oxidation in the range 1.15–1.73 V vs. SCE. Two successive bipyridine reductions are observed in the ranges −1.43 to −1.57 and −1.67 to −1.78 V vs. SCE. The complexes are susceptible to undergo stereoretentive oxidations to the trivalent ruthenium(III) congeners. The isolated one-electron paramagnetic ruthenium(III) complex, 1c + exhibits weak rhombic EPR spectrum at 77 K ( g 1=2.106, g 2=2.093, g 3=1.966) in 1:1 chloroform–toluene. The EPR spectrum of 1c + has been analyzed to furnish values of distortion parameters ( Δ=8988 cm −1; V=0.8833 cm −1) and energy of the expected ligand field transitions ( ν 1=1028 nm and ν 2=1186 nm) within the t 2 shell. One of the ligand field transitions has been experimentally observed at 1265 nm.

Paramagnetic ruthenium(III) ortho-metallated complexes. Synthesis, spectroscopic and redox properties

The reaction of (CS)Cl(PPh 3) 2Ru II (μ-Cl) 2 Ru II (PPh 3) 2Cl(CS), A with the phenolic Schiff base ligands o-(OH)C 6H 4C(H)N-C 6H 4(R), (R= p-OMe, Me, H, Cl, NO 2; H 2L 1–H 2L 5) in methanol under aerobic conditions afforded the complexes Ru III(HL) 2(PPh 3)Cl, 1 and Ru III(L)(PPh 3)(CH 3OH)Cl, 2. In complexes 1 both the ligands (HL −) are bound to the metal center at the deprotonated phenolic oxygen and azomethine nitrogen and in the complexes 2 the L 2− is in tridentate C,N,O mode where cyclometallation takes place from the ortho carbon atom of the amine fragment of H 2L. During the reaction the metal ion is oxidized from the starting Ru II in A to Ru III in the products 1 and 2. The complexes ( 1 and 2) are nonconducting and behave as one-electron paramagnets. Complexes display rhombic EPR spectra that have been analyzed to furnish values of axial (▵) and rhombic (V) distortion parameters as well as energies of the two expected ligand field transitions ( ν 1 and ν 2) within the t 2 shell. One of the transitions ( ν 2) has been observed in the predicted region. The complexes exhibit moderately strong ligand-to-metal charge-transfer transition in the visible region and intraligand transitions in the UV region. The complexes are electroactive and show ruthenium (IV)–ruthenium(III) ( E 1/2, 0.75–0.88 V vs. Ag/AgCl) and ruthenium(III)–ruthenium(II) ( E 1/2, −0.42 to −0.59 V) couples. The E 1/2 values vary linearly with the Hammett constant of the substituents R. The role of coordination of phenolato function in stabilizing the unusual paramagnetic ruthenium(III) oxidation state in the complexes 2 is noted.

Paramagnetic ruthenium(III) cyclometallated complex. Synthesis, spectroscopic studies and electron-transfer properties

The reaction of Ru II(PPh 3) 3X 2 (X = Cl, Br) with o-(OH)C 6H 4C(H)=N-CH 2C 6H 5 (HL) under aerobic conditions affords Ru II(L) 2(PPh 3) 2, 1, in which both the ligands (L) are bound to the metal center at the phenolic oxygen (deprotonated) and azomethine nitrogen and Ru III(L 1)(L 2)(PPh 3), 2, in which one L is in bidentate N,O form like in complex 1 and the other ligand is in tridentate C,N,O mode where cyclometallation takes place from the ortho carbon atom (deprotonated) of the benzyl amine fragment. The complex 1 is unstable in solution, and undergoes spontaneous oxidative internal transformation to complex 2. In solid state upon heating, 1 initially converts to 2 quantitatively and further heating causes the rearrangement of complex 2 to the stable RuL 3 complex. The presence of symmetry in the diamagnetic, electrically neutral complex 1 is confirmed by 1H and 31P NMR spectroscopy. It exhibits an Ru II → L, MLCT transition at 460 nm and a ligand based transition at 340 nm. The complex 1 undergoes quasi-reversible ruthenium(II)—ruthenium(III) oxidation at 1.27V vs. SCE. The one-electron paramagnetic cyclometallated ruthenium(III) complex 2 displays an L → Ru III, LMCT transition at 658 nm. The ligand based transition is observed to take place at 343 nm. The complex 2 shows reversible ruthenium(III)—ruthenium(IV) oxidation at 0.875V and irreversible ruthenium(III)—ruthenium(II) reduction at −0.68V vs. SCE. It exhibits a rhombic EPR spectrum, that has been analysed to furnish values of axial (6560 cm −1) and rhombic (5630 cm −1) distortion parameters as well as the energies of the two expected ligand field transitions (3877 cm −1 and 9540 cm −1) within the t 2 shell. One of the transitions has been experimentally observed in the predicted region (9090 cm −1). The first order rate constants at different temperatures and the activation parameter Δ H #/Δ S # values of the conversion process of 1 → 2 have been determined spectrophotometrically in chloroform solution.

Halfsandwich‐Type Triisopropylstibane Ruthenium Complexes with 16‐, 17‐, and 18‐Electron Configurations and an Unsymmetrical Binuclear 18/16‐Electron Ru2(SbiPr3) Species

AbstractThe paramagnetic ruthenium complex [(η5‐C5Me5)RuCl2‐{SbiPr3}] (2), which is prepared from [(η5‐C5Me5)RuCl2]n (1) and SbiPr3, reacts with Mg/Hg in THF to give the coordinatively unsaturated 16‐electron species (η5‐C5Me5)RuCl)(SbiPr3)] (3). Compound 3 is obtained in much better yield from [(η5‐C5Me5)Ru(μ3‐Cl)]4 (4) and SbiPr3 (molar ration 1:4). While 3 reacts with CO to give the 18‐electron complex [(η5‐C5Me5)RuCl(CO)(SbiPr3)] (5), on treatment of 3 with HCˇO2Me the metallacycle [(η5‐C5Me5)RuCl{k2(C,C)‐C(CO2Me}=CHC(CO2Me)=CH}(SbiPr3)] (6) is obtained. The reaction of 4 with SbiPr3 in the molar ratio of 1:2 affords the binuclear compound [(η5‐C5Me5)(SbiPr3)Ru(μ‐Cl)2Ru(‐C5Me5)] (7). The molecular structures of 2 and 7 have been determined by X‐ray crystallography.