Rhodium carbonyl complexes of bulky, anionic nitrogen-based ligands: A comparison of donating ability

Phosphinimine-imine ((C₆H₃i-Pr₂)NC(Me)CH₂PPh₂(NC₆H₃i-Pr₂))Rh(CO)₂ - (1) and β-diketiminate CH(C(Me)(Ni-Pr₂C₆H₃))₂Rh(CO)₂ - (2) rhodium dicarbonyl complexes were prepared as to elucidate any difference among these anionic, nitrogen-based ligands regarding donating ability to the rhodium center. Utilizing infrared spectroscopy and single crystal structural comparisons, differences in electron density donation by the ligands to the rhodium center were not observed. The carbonyl stretching frequencies of the aforementioned rhodium complexes were ν_CO = 2055, 1987 and 2055, 1988 for the phosphinimine-imine (1) and β-diketiminate (2) respectively.     

Stereochemistry of silicon tetrafluoride complexes with N- and O-donor ligands

Known experimental and theoretical data used in the analysis of stereoisomeric structures of penta-and hexacoordinate silicon tetrafluoride complexes with the molecular N-and O-donor ligands are discussed.     

The preparation and structural characterization of ruthenium carbonyl cluster complexes containing 3,3 dimethylthietane ligands

The reaction of Ru₃(CO)₁₂ with 3,3 dimethylthietane (DMT) at 68°C yielded the new tetraruthenium cluster complex Ru₄(CO)₁₂(-SCH₂CMe₂CH₂)₂,1 in 23% yield. Compound1 was characterized crystallographically and was shown to consist of a puckered square of four ruthenium atoms with two DMT ligands bridging opposite sides of the cluster via the sulfur atoms. Compound1 reacts with CO (98°C/1 atm) to yield the new tetraruthenium complex Ru₄(CO)₁₃ (-SCH₂CMe₂CH₂),2 in 69% yield. Compound2 consists of a butterfly tetrahedral cluster of four ruthenium atoms with a DMT ligand bridging the wing-tip metal atoms. Addition of DMT to2 regenerates1 in 67% yield. Crystal data—1: space group = ,a=17.490(2) Å,b=18.899(3) Å,c=9.781(1) Å, =93.06(1)°, =91.06(1)°, =105.239(9)°,Z=4, 5799 reflections,R=0.026; for2: space group = P2₁/n,a=15.430(3) Å,b=18.285(4) Å,c=9.850(2) Å, =90.05(2)°,Z=4, 2111 reflections,R=0.036.     

Synthesis,characterization and crystal structure of ruthenium(II) polypyridyl complexes

[Ru(bipy)2(5-R-phen)](ClO4)2 complexes have been prepared, where bipy=2,2- bipyridine, phen=1,10-phenanthroline, and R=H, Me, NO2 or NH2. The influence of the different 5- substituted phen on the electron delocalization and ligand-ligand interactions have been investigated by solution n.m.r.. The ligand- ligand interaction has also been observed in the solid state by determining the single crystal structure of [Ru(bipy)2(5- NO2-phen)](ClO4)2. The strong steric interaction between the polypyridyl ligands was relieved neither by the elongation of Ru–N bonds (2.055–2.086Å) nor by increase of N–Ru–N bite angles (77.8–79.4°), but rather by distortion of the coordination sphere by forming specific angles (=2.0, 3.2 and 4.2°) between the polypyridyl ligand planes and coordination planes (N–Ru–N), and larger torsion angles (5.8 and 8.2°) between the two pyridine rings for each bipy.     

Half-sandwich ruthenium(II) complexes with N- and N,(N,O)-donor ligands: molecular, electronic structures, and computational study

Four η⁶-p-cymene ruthenium(II) complexes with 2-(2-aminophenyl)-1H-benzimidazole (BImPhNH), 2-aminobenzimidazole (BImNH), 2-aminobenzothiazole (BTzNH), and 2-(2-hydroxyphenyl)benzoxazole (HBO) ligands have been prepared and studied by IR, ¹H-NMR, UV–Vis spectroscopy, and X-ray crystallography; its luminescent properties were examined. The experimental studies on the complexes have been accompanied computationally by the density functional theory (DFT) calculations.     

One-step entry to olefin-tethered N,S-heterocyclic carbene complexes of ruthenium with mixed ligands

A series of Ru(II) mixed-ligand complexes RuBr(2)(PPh(3))(2)(N-AyBzTh) (Ay = prop-2-enyl; BzTh = benzothiazol-2-ylidene) (4), RuBr(OAc)(PPh(3))(N-MeAyBzTh) (5), RuBr(OAc)(PPh(3))(N-MeBnBzTh)(2) (MeBn = 3-methylbut-2-enyl) (6) and RuCl(OAc)(PPh(3))(N-MeBnBzTh) (7) have been synthesized from Ru(OAc)(2)(PPh(3))(2) in one-pot condensation and ligand exchange reactions. X-ray single-crystal diffraction analysis revealed that they are neutral octahedral Ru(II) complexes with one or two N,S-heterocyclic carbene (NSHC) ligands and a coordinated (4, 5 and 7) or dangling (6) olefin arm. The system displays a range of self-selecting structural variations. Entry of the hybrid olefin-NSHC and halide ligands ejects either one (5, 6 and 7) phosphine ligand or keeps both phosphines (4) by replacing the acetate. It is also possible to accommodate two NSHC ligands by keeping the olefin pendant (6). Complexes 5 and 7 are isostructural with all different ligands on the coordination sphere. Complexes 4-6 are active towards transfer hydrosilylation showing good β(Z) selectivity, with the Ru(II) bearing acetate giving higher yields.     

Synthesis, photochemistry, and electrochemistry of ruthenium(II) polypyridyl complexes anchored by dicobalt carbonyl units

A novel hybrid complex system of ruthenium polypyridyl complexes anchored by dicobalt carbonyl units, [Ru(bpy)₂{phen-C{Co₂(CO)₄(dppm)}C-tolyl}](PF₆)₂ (1) and [Ru(bpy)₂{tolyl-C{Co₂(CO)₄(dppm)}C-phen-C{Co₂(CO)₄(dppm)}C-tolyl}](PF₆)₂ (2), has been prepared from the dicobalt carbonyl complex Co₂(CO)₆(dppm) (dppm = bis(diphenylphosphino)methane) and the ruthenium complex [Ru(bpy)₂(phen--tolyl)](PF₆)₂ (3) or [Ru(bpy)₂(tolyl--phen--tolyl)](PF₆)₂ (4).The present Ru-Co₂ hybrid complexes 1 and 2 are nonluminescent at room temperature, although precursor ruthenium polypyridyl complexes, such as 3 and 4, clearly show phosphorescence from the ³MLCT excited state. The emission quenching of these hybrid complexes indicates the intramolecular energy transfer from the ruthenium polypyridyl unit to the dicobalt carbonyl unit(s) and then to the ground state by a radiationless deactivation process accompanied by a vibrational relaxation of the dicobalt carbonyl unit(s). This interpretation is supported by spectral change measurements along with constant potential electrolysis and electrochemical data.     

Iron carbonyl cluster complexes with monophosphine ligands: synthesis,characterization, and crystal structure

Three new monophosphine-substituted iron carbonyl cluster complexes [(μ-PDT)Fe₂(CO)₅L] [(PDT = SCH₂CH₂CH₂S, L = P(CH₂Ph)₃, 1; P(C₆H₁₁)₃, 2; PPh₂(PhMe-p), 3)], which can be regarded as active site mimics for [FeFe]-hydrogenase, have been prepared in 40–70 % yields by reactions of the parent complex (μ-PDT)Fe₂(CO)₆ (A) with monophosphine ligands in the presence of the decarbonylating agent Me₃NO·2H₂O. All three complexes were characterized by elemental analysis and spectroscopic techniques, as well as by X-ray crystallography for complex 1. The IR spectra of the complexes reveal that the electron-donating abilities of the different monophosphine ligands follow the order PPh₂(PhMe-p) > P(C₆H₁₁)₃ > P(CH₂Ph)₃.     

Synthesis, characterization, and SAMs electroactivity of ruthenium complexes with sulfur containing ligands

The vibrational and ¹H NMR data hints that the coordination of the 2,2′-dithiodipyridine (2-pySS) ligand to the [Ru(CN)₅]³⁻ metal center occurs through the sulfur atom instead of the nitrogen atoms which is usually observed for N-heterocyclic ligands. Electrochemical results show that this coordination mode implies an additional thermodynamic stabilization of the Ru^II over Ru^III oxidation state due to a relative stronger π-back-bonding interaction with the empty low-lying dπ orbitals of the sulfur atom. Computational data reinforce the experimental results showing that the 2-pySS Lewis base centers are located on the sulfur atoms. Ligands containing only sulfur atoms as coordination sites (2,2′-dithiodipyridine N-oxide (2-pySSNO), 1,4-dithiane (1,4-dt), and 2,6-dithiaspiro[3.3]heptane (asp)) were also coordinated to the [Ru(CN)₅]³⁻ metal center to undoubtedly correlate the electrochemical results with the ligand coordination atom. Among the synthesized compounds, the [Ru(CN)₅(1,4-dt)]³⁻ and [Ru(CN)₅(asp)]³⁻ complexes showed to be able to form self-assembled monolayers (SAMs) on gold. These SAMs, which were characterized by SERS (surface-enhanced Raman scattering) spectroscopy, successfully assessed the heterogeneous electron transfer reaction of the cytochrome c metalloprotein in physiological medium.     

Preparation, characterization, and catalytic properties of ruthenium nitrosyl complexes with polypyrazolylmethane ligands

Ruthenium(II) nitrosyl complexes with polypyrazolylmethanes, [(Bpm)Ru(NO)Cl₃] [Bpm = bis(1-pyrazolyl)methane, 1], [(Bpm^∗)Ru(NO)Cl₃] [Bpm^∗ = bis(3,5-dimethyl-1-pyrazolyl)methane, 2], [(Tpm)Ru(NO)Cl₂][PF₆] [Tpm = tris(1-pyrazolyl)methane, 3], and [(Tpm^∗)Ru(NO)Cl₂][PF₆] [Tpm^∗ = tris(3,5-dimethyl-1-pyrazolyl)methane, 4], have been synthesized and characterized. The solid-state structures of [(Bpm^∗)Ru(NO)Cl₃] (2) and [(Tpm^∗)Ru(NO)Cl₂][PF₆] (4) were determined by single-crystal X-ray crystallographic analyses. These complexes have been tested as catalysts in the transfer hydrogenation of several ketones under mild conditions.     

Synthesis,characterization and in vitro biological activities of ruthenium(II) polypyridyl complexes

The ruthenium(II) polypyridyl complexes [Ru(dmb)₂(TCPI)](PF₆)₂ (1) and [Ru(ttbpy)₂(TCPI)](PF₆)₂ (2) (dmb = 4,4′-dimethyl-2,2′-bipyridine, TCPI = 2-(3-(1H-1,3,7,8-tetraazacyclopenta[l]phenanthren-2-yl)phenyl)benzo[de]isoquinoline-1,3-dione, ttbpy = 4,4′-ditertiary butyl-2,2′-bipyridine) were synthesized and characterized. The in vitro cytotoxicities of the complexes were examined against a panel of cancer cell lines including SGC-7901, PC-12, HepG-2, SiHa, Eca-109, HeLa, Eca-9706, HOS and LO₂ by 3-(4,5-dimethylthiazole)-2,5-diphenyltetrazolium bromide (MTT) method. Both complexes show higher activities against PC-12 cells, with IC₅₀ values of 34.4 ± 1.3 and 26.8 ± 2.4 μM for 1 and 2, respectively. Cell apoptosis was assayed with acridine orange (AO) and ethidium bromide (EB) and annexin V/PI staining methods using fluorescence microscopy and flow cytometry. The reactive oxygen species, mitochondrial membrane potential and cell cycle distribution were assessed. Cell invasion was determined by Matrigel invasion assay, and the proteins associated with cell apoptosis were analyzed by western blot. The results suggest that the complexes induce the apoptosis of PC-12 cells through a ROS-mediated mitochondrial dysfunction pathway, accompanied by regulation of the expression of caspases and Bcl-2 family proteins.     

Synthesis,characterization and interaction of mixed polypyridyl ruthenium(II) complexes with calf thymus DNA

New mixed polypyridyl {HPIP = 2-(2-hydroxyphenyl)imidazo[4,5-f][1,10]phenanthroline, phen = 1,10-phenanthroline, dmp = 2,9-dimethyl-1,10-phenanthroline, dmb = 4,4-dimethyl-2,2-bipyridine} ruthenium(II) complexes [Ru(phen)₂(HPIP)]²⁺, [Ru(dmp)₂(HPIP)]²⁺ and [Ru(dmb)₂(HPIP)]²⁺ were synthesized and characterized by elemental analyses ¹H-n.m.r., u.v.–vis. spectroscopy and cyclic voltammetry. Their DNA-binding properties were demonstrated by absorption, luminescence titrations, steady-state emission quenching and viscosity measurements. The results suggested that all the examined complexes bind with CT-DNA intercalatively. Methyl groups substituted at the 4,4-positions of bpy has no obvious effect on its DNA binding, whereas substituents at the 2- and 9-positions of phen have an impressive effect on its DNA-binding, as revealed by the decreased binding affinity.     

Synthesis,characterization, and cytotoxic and antimicrobial activities of ruthenium(II) arene complexes with N,N-bidentate ligands

Three new complexes, [(η⁶-C₆H₆)RuCl(C₅H₄N-2-CH=N-Ar)]PF₆ (Ar = phenylmethylene (1), (4-methoxyphenyl)methylene (2), and phenylhydrazone (3)), were prepared by reacting [(η⁶-C₆H₆)Ru(μ-Cl)Cl]₂ with N,N′-bidentate ligands in a 1 : 2 ratio. Full characterization of the complexes was accomplished using ¹H and ¹³C NMR, elemental and thermal analyses, UV–vis and IR spectroscopy and single crystal X-ray structures. Single crystal structures confirmed a pseudo-octahedral three-legged, piano-stool geometry around Ru(II), with the ligand coordinated to the ruthenium(II) through two N atoms. The cytotoxicity of the mononuclear complexes was established against three human cancer cell lines and selectivity was also tested against non-cancerous human epithelial kidney (HEK 293) cells. The compounds were selective toward the tumor cells in contrast to the known anti-cancer drug 5-fluoro uracil which was not selective between the tumor cells and non-tumor cells. All the compounds showed moderate activity against MCF7 (human breast adenocarcinoma), but showed low antiproliferative activity against Caco-2 and HepG2. Also, antimicrobial activities of the complexes were tested against a panel of antimicrobial-susceptible and -resistant Gram-negative and Gram-positive bacteria. Of special interest is the anti-mycobacterial activity of all three synthesized complexes against Mycobacterium smegmatis, and bactericidal activity against resistant Enterococcus faecalis and methicillin-resistant Staphylococcus aureus ATCC 43300.     

Diastereoselectivity at chiral metal center of half-sandwich-type ruthenium complexes with planar-chiral cyclopentadienyl ligands in multiple ligand transfer reaction

The triple ligand transfer reaction between planar-chiral cyclopentadienyl-ruthenium complexes [Cp′Ru(NCMe)₃][PF₆] (1) (Cp′ = 1-(COOR²)-2-Me-4-R¹C₅H₂; R¹ = Me, Ph, t-Bu) and iron complexes CpFe(CO)(L)X (2) (L = PMe₃, PMe₂Ph, PMePh₂, PPh₃; X = I, Br) resulted in the formation of metal-centered chiral ruthenium complexes Cp′Ru(CO)(L)X (3) in moderate yields with diastereoselectivities of up to 68% de. The configurations of some major diastereomers were determined to be by X-ray crystallography. The diastereoselectivity of 3 was under kinetic control and not affected by the steric effect of the substituents on the Cp′ ring of 1 and the phosphine of 2. Although the double ligand transfer reaction between [Cp′Ru{P(OMe)₃}(NCMe)₂][PF₆] (7) and CpFe(CO)₂X (8) produced Cp′Ru{P(OMe)₃}(CO)X (9), the selectivity at the ruthenium center was low.     

Dinuclear ruthenium(II) polypyridyl complexes containing large, redox-active, aromatic bridging ligands: synthesis, characterization, and intramolecular quenching of MLCT excited states

Two new ruthenium(II) polypyridyl dimers containing the large planar aromatic bridging ligands 9,11,20,22-tetraazatetrapyrido[3,2-a:2'3'-c:3' ',2'-l:2',3'-n]pentacene (tatpp) and 9,11,20,22-tetraazatetrapyrido[3,2-a:2'3'-c:3',2' '-l:2',3'-n]pentacene-10,21-quinone (tatpq) have been synthesized and characterized by (1)H and (13)C NMR, MALDI mass spectrometry, and elemental analyses. The electronic properties (UV-vis, redox, photophysical) of these dimers are analyzed in the context of orbital calculations (PM3 level) on the bridging ligands. A localized orbital model is proposed in which low-lying acceptor orbitals on the center portion of the ligands effectively quench the Ru(II)-based MLCT emission via a mechanism that can be viewed as intramolecular electron transfer to specific subunits of the bridges.     

Preparation, characterization and structure of ruthenium phosphine complexes containing non-innocent ligands

Phosphine ruthenate complexes containing the non-innocent ligands 4-chloro-1,2-phenylenediamine (opda-Cl) and 3,3′,4,4′-tetraamminebiphenyl (diopda) were synthesized and characterized by means of X-ray diffraction, electrochemistry, ³¹P{¹H} NMR and electronic spectroscopies. Crystals of cis-[RuCl₂(dppb)(bqdi-Cl)] complex were isolated as a mixture of two conformational isomers due to different positions of the chlorine atoms of the o-phenylene ligand in relation to the P1 atom of the phosphine moiety.     

Di- and tetranuclear ruthenium(II) and/or osmium(II) complexes of polypyridyl ligands bridged by a fully conjugated aromatic spacer: synthesis,characterization, and electrochemical and photophysical studies

A series of mono-, di-, and tetranuclear homo/heterometallic complexes of Ru(II) and Os(II) based on the bridging ligand dppz(11-11')dppz (where dppz = dipyrido[3,2-a:2',3'-c]phenazine) (BL) have been synthesized and characterized. This bridging ligand is a long rigid rod with only one rotational degree of freedom and provides complete conjugation between the chromophores. The complexes synthesized are of general formula [(bpy)(2)Ru-BL](2+), [(phen)(2)/(bpy)(2)M-BL-M(bpy)(2)/(phen)(2)](4+) (M = Ru(II) and Os(II)), [(bpy)(2)Ru-BL-Os(bpy)(2)](4+), and [((bpy)(2)Ru-BL)(3)M](8+). Detailed (1)H NMR studies of these complexes revealed that each chiral center does not influence its neighbor because of the long distance between the metal centers and the superimposed resonances of the diastereoisomers, which allowed the unambiguous assignment of the signals, particularly for homonuclear complexes. Concentration-dependent (1)H NMR studies show molecular aggregation of the mono- and dinuclear complexes in solution by pi-pi stacking. Electrospray mass spectrometry data are consistent with dimerization of mono- and dinuclear complexes in solution. Electrochemical studies show oxidations of Ru(II) and Os(II) in the potential ranges +1.38 to +1.40 and +0.92 to +1.01 V, respectively. The bridging ligand exhibits two one-electron reductions, and it appears that the added electrons are localized on the phenazene moieties of the spacer. All of these complexes show strong metal-to-ligand charge-transfer (MLCT) absorption and (3)MLCT luminescence at room temperature. Quantum yields have been calculated, and the emission lifetimes of all complexes have been measured by laser flash photolysis experiments. The luminescence intensity and lifetime data suggest that the emission due to the Ru center of the heteronuclear complexes is strongly quenched (>90%) compared to that of the corresponding model complexes. This quenching is attributed to intramolecular energy transfer from the Ru(II) center to the Os(II) center (k = (3-5) x 10(7) s(-1)) across the bridging ligand.     

Synthesis, characterization, reactivity and theoretical studies of ruthenium carbonyl complexes containing ortho-substituted triphenyl phosphanes

A series of ruthenium o-phosphane complexes was synthesized and characterized. The reactivity of the prepared complexes was studied by using them as catalysts for the hydroformylation of 1-hexene. The activities depended on the binding mode of the phosphane and on the strength of the ruthenium-phosphane interaction. Strongly coordinated chelating [2-(dimethylamino)phenyl]-(diphenyl) phosphane and [2-(methylthio)phenyl]-(diphenyl) phosphane showed poor activity, while weakly chelated [2-(methoxy)phenyl]-(diphenyl) phosphane and non-chelating phosphanes such as [2-(methyl)phenyl]-(diphenyl) phosphane or [2-(ethyl)phenyl]-(diphenyl) phosphane led to higher activities.     

Synthesis, characterization, electro chemistry, catalytic and biological activities of ruthenium(III) complexes with bidentate N, O/S donor ligands

New hexa-coordinated ruthenium(III) complexes of the type [RuX(2)(EPh(3))(2)(L)] (E=P or As; X=Cl or Br; L=monobasic bidentate Schiff base derived from the condensation of benzhydrazide with furfuraldehyde, 2-acetylfuran and 2-acetylthiophene) have been synthesized from the equimolar amounts of [RuX(3)(EPh(3))(3)] or [RuBr(3)(PPh(3))(2)(MeOH)] and Schiff bases in benzene. The new complexes have been characterized by analytical, spectral (IR, electronic and EPR), magnetic moment, and cyclic voltammetry. An octahedral structure has been tentatively proposed. All the complexes have exhibited catalytic activity for the oxidation of benzyl alcohol, cyclohexanol and cinnamylalcohol in the presence of N-methylmorpholine-N-oxide as co-oxidant. All the new complexes were found to be active against the bacteria such as E. coli, Pseudomonas, Salmonella typhi and Staphylococcus aureus. The activity was compared with standard Streptomycin.