Heterocyclic Nitrogen Donor Research Articles

Copper(II) complexes containing derivative of aminobenzoic acid and nitrogen-rich ligands: Synthesis, characterization and cytotoxic potential

Four mixed ligand copper(II) complexes bearing mefenamic acid and different heterocyclic nitrogen donor ligands have been synthesized. A direct one-step metal-ligand complexation method was adopted in synthesizing the complexes. These newly formed complexes are [Cu(mef)2(imi)2]; CM-1, [Cu(mef)2(py)2]; CM-2, [Cu2(mef)4(apy)2].2CH3CN; CM-3, and [Cu(mef)2(nic)2(C2H5OH)]; CM-4 (mef = mefenamato, imi = imidazole, py = pyridine, apy = 2-aminopyridine, and nic = nicotinamide). The complexes were characterized by both analytical and spectral methods. FTIR studies confirmed the mefenamato ligand coordinated via a deprotonated carboxylato oxygen atom to the Cu(II) center. The molecular structures of CM-1 and CM-2 showed both are isostructural and exhibit square-planar geometry around Cu(II). CM-3 crystallized in the dimeric form, each Cu(II) is in five-coordinate geometry, with a structural paddle wheel motif. The resulting square pyramidal geometry in CM-4 is due to the ethanol solvent's coordination on the pyramid's axial position. The crystal lattice of the complexes was stabilized by noncovalent interactions such as N-H···O, C-H···O, CH···π, and π···π. The mononuclear complexes were more stable than the dimeric complex CM-3, revealed by thermogravimetric analysis. In addition, the cytotoxic study of the copper (II) complexes on lung carcinoma cells (NCIH-460) and breast cells (MDAMB) were evaluated using MTT dye (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide) assay.

Mixed Ligand Complexes of Cobalt(II): Synthesis, Reactivity, Physico-Chemical and Spectroscopic Studies

The mixed ligand complexes of Co(II) metal ions with some heterocyclic nitrogen bases along with 1-cyano-1-carboethoxyethylene-2,2-dithiolate ion (CED2−) of the compositions, Co(N-N)(CED)·2H2O [N-N = o-phen/2,2′-bipy] and Co(N-N)(CED)L2 [N-N = o-phen/2,2′-bipy, CED2– = 1-cyano-1- carboethoxyethylene-2,2-dithiolate, L = γ-picoline (γ-pic), β-picoline (β-pic), α-picoline (α-pic), pyridine (py)] were characterized and isolated by analytical data as well as physico-chemical methods for example infrared spectroscopy, electronic, magnetic susceptibility, molar conductance. The complexes are soluble in coordinating solvents like DMSO and DMF and decompose below 250 ºC. The synthesized complexes in DMF solution are non-electrolytic as shown by their molar conductance data. The calculated magnetic moments suggest that the synthesixed cobalt(II) compounds are paramagnetic and produce a low-spin environment for the Co(II) ion. Thermal studies reveal that Co(N-N) contains two coordinated water molecules (CED)·2H2O. Electronic spectra of cobalt(II) complexes with mixed ligands in DMF solution are consistent with distorted octahedral stereochemistry. The IR studies indicates that the CED2- ion exhibits bidentate chelating behaviour and that heterocyclic nitrogen donors coordinate to Co atoms (II). Reaction with heterocyclic nitrogen donors (γ-picoline, β-picoline, α-picoline, pyridine) signifying the ligand exchange reaction.

Heterocyclic nitrogen donor complexes of aluminium, gallium and indium with weakly coordinating triflate anions

The reactions of M(OTf)3 (M = Al, Ga, In; OTf = CF3SO3–) with 2,2′:6′,2′’- terpyridyl (terpy) in CH2Cl2 gave mer-[M(OTf)3(terpy)], whilst with 2,2′-bipyridyl (bipy) and 1,10-phenanthroline (phen) the products isolated were cis-[M”(OTf)2(bipy)2]OTf (M” = Al, Ga), cis-[In(OTf)(H2O)(bipy)2][OTf]2, cis-[Al(OTf)2(phen)2][OTf] and [In(H2O)2(phen)2][OTf]3. The X-ray structures of mer-[In(OTf)3(terpy)], cis-[Ga(OTf)2(bipy)2][OTf] and cis-[In(OTf)(H2O)(bipy)2][OTf]2, along with those of the minor by-products, cis-[Ga(H2O)2(phen)2][OTf]3 and the hydroxide-bridged dimer [{In(terpy)(OTf)}2(µ-OH)2][OTf]2 were also obtained, all of which show six-coordination at the metal ion. While the anhydrous complexes show κ1-coordination of the triflate to the metal ion, those species with coordinated water (or hydroxide) ligands show significant H-bonding interactions between the water H atoms and the O-atoms from triflate anions. The complexes were characterised by IR, 1H, 13C{1H}, 19F{1H} and 27Al NMR spectroscopy, together with microanalysis. The 19F{1H} NMR spectra suggest that in MeCN solution the coordinated triflates are displaced by the solvent, but the original complexes appear to reform on removal of the MeCN in vacuo.

Influence of a Heterocyclic Nitrogen-Donor Group on the Coordination of Trivalent Actinides and Lanthanides by Aminopolycarboxylate Complexants

The novel metal chelator N-2-(pyridylmethyl)diethylenetriamine-N,N',N″,N″-tetraacetic acid (DTTA-PyM) was designed to replace a single oxygen-donor acetate group of the well-known aminopolycarboxylate complexant diethylenetriamine-N,N,N',N″,N″-pentaacetic acid (DTPA) with a nitrogen-donor 2-pyridylmethyl. Potentiometric, spectroscopic, computational, and radioisotope distribution methods show distinct differences for the 4f and 5f coordination environments and enhanced actinide binding due to the nitrogen-bearing heterocyclic moiety. The Am3+, Cm3+, and Ln3+ complexation studies for DTTA-PyM reveal an enhanced preference, relative to DTPA, for trivalent actinide binding. Fluorescence studies indicate no changes to the octadentate coordination of trivalent curium, while evidence of heptadentate complexation of trivalent europium is found in mixtures containing EuHL(aq) complexes at the same aqueous acidity. The denticity change observed for Eu3+ suggests that complex protonation occurs on the pyridyl nitrogen. Formation of the CmHL(aq) complex is likely due to the protonation of an available carboxylate group because the carbonyl oxygen can maintain octadentate coordination through a rotation. The observed suppressed protonation of the pyridyl nitrogen in the curium complexes may be attributed to stronger trivalent actinide binding by DTTA-PyM. Density functional theory calculations indicate that added stabilization of the actinide complexes with DTTA-PyM may originate from π-back-bonding interactions between singly occupied 5f orbitals of Am3+ and the pyridyl nitrogen. The differences between the stabilities of trivalent actinide chelates (Am3+, Cm3+) and trivalent lanthanide chelates (La3+-Lu3+) are observed in liquid-liquid extraction systems, yielding unprecedented 4f/5f differentiation when using DTTA-PyM as an aqueous holdback reagent. In addition, the enhanced nitrogen-donor softness of the new DTTA-PyM chelator was perturbed by adding a fluorine onto the pyridine group. The comparative characterization of N-(3-fluoro-2-pyridylmethyl)diethylenetriamine-N,N',N″,N″-tetraacetic acid (DTTA-3-F-PyM) showed subdued 4f/5f differentiation due to the presence of this electron-withdrawing group.

Kinetics and mechanism of the substitution reactions of some monofunctional Pt(II) complexes with heterocyclic nitrogen donor molecules. Crystal structure of [Pt(bpma)(pzBr)]Cl2·2H2O

Substitution reactions of [Pt(terpy)Cl]+ (terpy = 2,2′;6′,2′′-terpyridine), [Pt(bpma)Cl]+ (bpma = bis(2-pyridylmethyl)amine), [Pt(dien)Cl]+ (dien = diethylenetriamine or 1,5-diamino-3-azapentane) and [Pt(tpdm)Cl]+ (tpdm = tripyridinedimethane) with nitrogen donor heterocyclic molecules, such as 3-amino-4-iodo-pyrazole (pzI), 5-amino-4-bromo-3-methyl-pyrazole (pzBr) and imidazole (Im), were studied in aqueous 0.10 M NaClO4 in the presence of 10 mM NaCl using variable-temperature UV–vis spectrophotometry. The second-order rate constants k2 indicate decrease in reactivity in the order [Pt(terpy)Cl]+ > [Pt(bpma)Cl]+ > [Pt(tpdm)Cl]+ > [Pt(dien)Cl]+. The most reactive nucleophile among the heterocyclic compounds is imidazole, while pzI shows slightly higher reactivity than pzBr. Activation parameters were also determined and the negative values for entropies of activation, ΔS≠, support an associative mode of substitution for all substitution processes. Crystal structure of [Pt(bpma)(pzBr)]Cl2·2H2O was determined by single-crystal X-ray analysis. The coordination geometry of the complex is distorted square-planar while the bond distance Pt–N2(pzBr) is longer than the other three Pt–N distances.

Effect of heterocyclic nitrogen donor ligands on coordination behavior of weakly coordinating arylsulfonate: Synthesis, characterization and antimicrobial activities of [Cu(β-pic)4(2-Cl-5-nitrobenzenesulfonate)2](methanol) and [Cu(γ-pic)4(2-Cl-5 nitrobenzenesulfonate)2

Two new copper(II) complexes [Cu(β-pic)4(2-Cl-5-nitrobenzenesulfonate)2](CH3OH) (1) and [Cu(γ-pic)4(2-Cl-5-nitrobenzenesulfonate)2] (2) have been synthesized by reacting appropriate starting materials in methanol:water (v/v 4:1). Both newly synthesized complexes have been characterized on the basis of elemental analyses, spectroscopic techniques (FT-IR, UV–Vis, EPR) and single crystal X-ray structure determination (complex 1). The structural analysis of complex 1 revealed the existence of unusual coordination behavior of arylsulfonate towards copper(II) center in presence of heterocyclic N-donor ligands resulting in elongated octahedral geometry around the metal. The EPR spectroscopy of complexes 1 and 2 unambiguously proved a similar coordination of four picolines in Cu(II) xy plane. Antimicrobial studies of both the complexes 1 and 2 were performed against Gram positive, MRSA (Methicillin-Resistant Staphylococcus aureus) as well as Gram negative (Escherichia coli, Klebsiella pneumoniae) bacteria. The activity was investigated by using both Agar well diffusion as well as MIC assay. Both the complexes show significant bactericidal activity against all the pathogenic strains in comparison to ampicillin, a broad spectrum antibiotic against Gram positive and Gram negative bacteria.

Synthesis and photoluminescent behavior of Eu(III) complexes with 4,4,4-trifluoro-1-(6-methoxy-naphthalen-2-yl)-butane-1,3-dione

The fluorinated β-diketone ligand, 4,4,4-trifluoro-1-(6-methoxy- naphthalen-2-yl)-butane-1,3-dione (HL), and its ternary europium (III) complexes using water (H2O), 2,2-dipyridine (Bipy), 1,10-phenanthroline (Phen) and 4′-phenyl-terpyridine (Phterpy) as the secondary ligand were synthesized and characterized by elemental analysis, FT-IR, 1H NMR, UV–vis absorption, ESI–MS and fluorescence spectroscopic techniques. All these europium complexes exhibited the characteristic emission bands that arise from the 5D0→7FJ (J=0–4) transitions of the europium ion in solid state. Based on their emission spectra and lifetimes, the Judd–Ofelt intensity parameters (Ω2 and Ω4), the radiative decay rate Arad, the nonradiative rates Anrad, and the quantum efficiency (η) were determined and compared. The ternary complexes, EuL3·Bipy, EuL3·Phen and EuL3·Phterpy, exhibited much higher quantum efficiencies and lifetime values, which can be attributed to the displacement of water molecules from the coordination sphere by the heterocyclic nitrogen donors. Especially, the complex EuL3·Phen exhibited the longest lifetime τ (0.704ms) and the highest luminescence quantum efficiency η (47.9%) among these complexes. Meanwhile, complexes EuL3·Bipy, EuL3·Phen and EuL3·Phterpy also displayed higher Ω2 values than the complex EuL3·2H2O, indicating their hypersensitive character of the 5D0→7F2 transition and a highly polarizable chemical environment around the europium(III) ion.

Synthesis and Structural Studies of Some New Cobalt (II) Complexes with Chloride and Heterocyclic Nitrogen Donor ligands

A new series of cobalt complexes of type [Co(L)6]Cl2 (where L =imidazole, pyridine, piperidine, piperazine, indole, triazole, benzimidazole, benzotriazole, quinoline, iso-quinoline and carbazole) have been synthesized and are well characterized by elemental analysis, IR, UV, Mass spectra and magnetic measurements. The thermal studies of these complexes are also reported. All these complexes are soluble in ethanol and the conductance measurement shows that all the complexes are of 1:2 type electrolyte. The IR spectra show clear indication for coordination between central cobalt atom and nitrogen atom of the ligands. The mass spectra clearly show the molecular ion peak and base peak at appropriate place. On thermo gravimetric analysis, it is found that the metal atom and chlorine are strongly attached to each other. The ligands are loosely attached and are removed first on heating. Finally considering all the spectral analysis, conductance values, thermo gravimetric analysis, octahedral structure are proposed for these complexes

Synthesis, Characterization and Antifungal Activity of Adducts of Bis(acetylacetonato)oxovanadium(IV) with Heterocyclic Nitrogen Donor Ligands

Monomeric six coordinated adducts of bis(acetylacetonato)oxovanadium(IV) having general formula, [VO(acac)2(L)], [L= pyrrolidine, morpholine, 2,4,6-trimethylpyridine, 2,4, 2,6, 3,4, 3,5-dimethylpyridines, 2-ethylpyridine, 2-methylpyridine, 3-methylpyridine 2, 3, 4-cyanopyridine, quinoline, isoquinoline] have been synthesized and characterized by elemental analysis, IR, electronic spectroscopy, magnetic and conductivity measurements having 1:1 stoichiometry. The adducts were found to be paramagnetic and their magnetic moments at room temperature lie within the 1.72-1.87 B.M. range and this indicates the presence of one unpaired electron. The values are in accordance with the octahedral geometry. The magnetic moment measurements and electronic spectra depicts a octahedral geometry around the vanadium center. The investigated adducts have also tested against the fungus Fusarium oxysporum.

Synthesis and Characterization of mixed ligand complexes of Co(II) ion with some N and S donor

Mixed ligand complexes of Co(II) ion with some heterocyclic nitrogen donors and 1,1-dicyanoethylene-2,2-dithiolate of the compositions, Co(N-N)2(i-MNT), Co(N-N)(i-MNT).2H2O and Co(N-N)(i-MNT)L2 (N-N = 1,10-phenanthroline, 2,2'-bipyridine ; i-MNT 2- = 1,1-dicyano- ethylene -2,2- dithiolate ; L = pyridine(py), -picoline (-pic), -picoline (-pic) or -picoline (-pic) have been isolated and characterized on the basis of analytical data, molar conductance, magnetic susceptibility, electronic and infrared spectral studies. The molar conductance data reveal non-electrolytic nature of the complexes in DMF. Magnetic moment values suggest low spin complexes. The electronic spectral data suggest distorted octahedral stereochemistry around Co(II) ion in these complexes. Infrared spectral studies suggest bidentate chelating behaviour of i-MNT 2- , 1,10-phenanthroline and 2,2'-bipyridine while other ligands show unidentate

3D Coordination Network of Ag(I) Ions with μ 3 -Bridging Melamine Ligands

A new 3D silver complex [Ag(mela)(H2O)(NO3)]n (1) (mela = melamine or 2,4,6-triaminotriazine) is synthesized and characterized by single crystal X-ray diffraction, IR, and elemental analysis. The structural characterization shows that the compound crystallizes in space group C c, a = 8.181(2), b = 10.269(3) c = 11.347(3) A, β = 105.88(2)°, Z = 4. Out of several structurally characterized transition metal compounds comprising melamine, the titled complex represents a rare example of μ 3 -melamine coordination mode realized through the heterocycle nitrogen donors. The fluorescent property of complex 1 was investigated and the mechanism was validated by means of a density functional theory (DFT) calculation. A new 3D silver complex was synthesized using the 2,4,6-triaminotriazine ligand. The X-ray structural analysis shows a highly distorted trigonal bipyramidal geometry of Ag(I) ion with a rare μ3-coordination mode of the ligand achieved through the heterocyclic nitrogen donors. Emission study reveals intraligand and ligand-to-metal charge transfer in the complex.

Synthesis and structural characterization of manganese(III, IV) and ruthenium(III) complexes derived from 2-hydroxy-1-naphthaldehydebenzoylhydrazone

Reaction of 2-hydroxy-1-naphthaldehydebenzoylhydrazone(napbhH2) with manganese(II) acetate tetrahydrate and manganese(III) acetate dihydrate in methanol followed by addition of methanolic KOH in molar ratio (2 : 1 : 10) results in [Mn(IV)(napbh)2] and [Mn(III)(napbh)(OH)(H2O)], respectively. Activated ruthenium(III) chloride reacts with napbhH2 in methanolic medium yielding [Ru(III)(napbhH)Cl(H2O)]Cl. Replacement of aquo ligand by heterocyclic nitrogen donor in this complex has been observed when the reaction is carried out in presence of pyridine(py), 3-picoline(3-pic) or 4-picoline(4-pic). The molar conductance values in DMF (N,N-dimethyl formamide) of these complexes suggest non-electrolytic and 1 : 1 electrolytic nature for manganese and ruthenium complexes, respectively. Magnetic moment values of manganese complexes suggest Mn(III) and Mn(IV), however, ruthenium complexes are paramagnetic with one unpaired electron suggesting Ru(III). Electronic spectral studies suggest six coordinate metal ions in these complexes. IR spectra reveal that napbhH2 coordinates in enol-form and keto-form to manganese and ruthenium metal ions in its complexes, respectively. ESR studies of the complexes are also reported.

Synthesis and characterization of manganese(IV) and ruthenium(III) complexes derived from bis (2-hydroxy-1-naphthaldehyde)oxaloyldihydrazone

Bis(2-hydroxy-1-naphthaldehyde)oxaloyldihydrazone(naohH4) interacts with manganese(II) acetate in methanol followed by addition of KOH giving [MnIV(naoh)(H2O)2]. Activated ruthenium(III) chloride reacts with naohH4 in methanol yielding [RuIII(naohH4)Cl(H2O)Cl2]. The replacement of aquo by heterocyclic nitrogen donor in these complexes has been observed when the reaction is carried out in presence of heterocyclic nitrogen donors such as pyridine(py), 3-picoline(3-pic) or 4-picoline(4-pic). The molar conductance values in DMF for these complexes suggest non-electrolytic nature. Magnetic moment values suggest +4 oxidation state for manganese in its complexes, however, ruthenium(III) complexes are paramagnetic with one unpaired electron. Electronic spectral studies suggest six coordinate metal ions. IR spectra reveal that naohH4 coordinates in enol-form and keto-form to manganese and ruthenium, respectively. ESR and cyclic voltammetric studies of the complexes have also been reported.

Sterically hindered complexes of platinum(II) with planar heterocyclic nitrogen donors. A novel complex with 1-methyl-cytosine has a spectrum of activity different from cisplatin and is able of overcoming acquired cisplatin resistance

A very interesting series of water soluble platinum compounds violating some of the classical structure–activity relationships, but still showing antitumor activity, was reported by Hollis and collaborators some 25 years ago [L.S. Hollis, A.R. Amundsenm, E.W. Stern. J. Med. Chem. 32 (1989) 128–136]. The compounds, having formula [PtClA2L]+ (A2=two monodentate or a bidentate amine, L=a secondary or tertiary amine or a N-donor heterocycle), were characterized by a positive charge and three non-labile N-donor ligands. We have extended the investigation to analogous compounds in which 2,9-dimethyl-1,10-phenanthroline has taken the place of the A2 ligand(s) and L is 2-picoline (1), 6-amino-2-picoline (2), or 1-methyl-cytosine (3). The X-ray analysis of 2 has revealed a bow-like distortion of the phenanthroline plane, a sloping of the phenanthroline plane with respect to the coordination plane, and an overall shielding of the metallic core by the ortho substituents of the phenanthroline and pyridine ligands.In vitro grow inhibition assays have been performed on the most water soluble complex 3. The results indicate that this complex is characterized by a potent growth inhibitory activity with mean IC50 value (in a panel of 11 human tumor cell lines) of 1.1μM to be compared with a mean value of 3.8μM for cisplatin. The same compound also appears to completely overcome the acquired cisplatin resistance stemming from reduced uptake or a multifocal mechanism, thus pointing to a mechanism of action distinctly different from that of cisplatin.

Structure and Characterization of Fe(III) Complexes with a Square Planar Ligand and the Effect by the Introduction of External Monodentate Axial Ligands

A square planar iron complex with H2babp was synthesized and its coordination behaviors with monodentate axial ligands were studied. Cl– or imidazole ligand coordinated at the axial positions of the complex, but pyridine could not be introduced. The heterocyclic nitrogen donors, such as pyridine and imidazole, abstracted the amide protons of the ligand H2babp [1]. The oxidation reactivity was controlled by the presence or absence of amide protons of planar ligand H2babp rather than the axial ligands. The oxidation of cyclohexene by their complexes in the presence of PhIO proceeded catalytically when the iron complexes with protonated H2babp was used, while only a slight amount of oxidation products were obtained when the complexes with deprotonated babp2– were used.

Extended three-dimensional supramolecular architectures derived from trinuclear (bis-β-diketonato)copper(ii) metallocycles

Neutral trinuclear (triangular) copper(II) complexes of type [Cu3L3] incorporating the 1,4-aryl linked bis-beta-diketonato bridging ligands, 1,1-(1,4-phenylene)-bis(butane-1,3-dione) (H2L2), 1,1-(1,4-phenylene)-bis(pentane-1,3-dione) (H2L3) and 1,1-(1,4-phenylene)-bis(4,4-dimethylpentane-1,3-dione) (H2L4) have been demonstrated to react with selected heterocyclic nitrogen donor bases to generate extended supramolecular architectures whose structures have been confirmed by X-ray diffraction. Thus on reaction with 4,4'-bipyridine (bipy), [Cu3(L2)3] yields polymeric structures of type {[Cu3(L2)3(bipy)(THF)] x 2.75THF}n and {[Cu3(L2)3(bipy)(THF)] x bipy x 0.75THF}(n) while with pyrazine (pyz), {[Cu3(L2)3(pyz)] x 0.5THF}n was obtained. Each of these extended structures contain alternating triangle/linker units in a one-dimensional polymeric chain arrangement in which two of the three copper sites in each triangular 'platform' are formally five-coordinate through binding to a heterocyclic nitrogen atom. Interaction of the multifunctional linker unit hexamethylenetetramine (hmt) with [Cu3(L3)3] afforded an unusual, chiral, three-dimensional molecular framework of stoichiometry [Cu3(L3)3(hmt)]n. The latter incorporates the trinuclear units coordinated to three triply bridging hmt units. In marked contrast to the formation of the above structures incorporating bifunctional linker units and five-coordinate metal centres, the trinuclear platform [Cu3(L2)3] reacts with the stronger difunctional base 1,4-diazabicyclo[2.2.2]-octane (dabco) to yield a highly symmetric trigonal columnar species of type {[Cu3(L4)3(dabco)3] x 3H2O}n in which each copper centre is octahedrally coordinated.

Spectroscopic and thermal studies of some Palladium complexes with certain Heterocyclic Nitrogen ligands

Mono- and binuclear palladium complexes were isolated from reactions of [PdCl4]2− with heterocyclic nitrogen donor ligands depending on the type of ligand. Bidentate ligands L–L, where L–L = 2-(2′-pyridyl)-benzimidazole (PBI), 2-pyrazinecarboxylic acid (PC) and 2-pyrazinecarboxamide (PCA) gave the monosubstituted [Pd(L-L)Cl2] complex. Binuclear palladium complexes [Pd(L)Cl2]2 were obtained from reactions with the monodentate ligands 2-aminothiazole (AT) or 2-aminobenzimidazole (ABI). Elemental analyses and spectroscopic studies of the reported complexes allowed structures to be proposed. The thermal properties of the complexes were also investigated by thermogravimetric techniques.

Intramolecular Hydroamination Catalyzed by Cationic Rhodium and Iridium Complexes with Bidentate Nitrogen-Donor Ligands

Cationic rhodium(I) and iridium(I) complexes of the general formula [M(N−N)(CO)2]+[X]-, incorporating the bidentate heterocyclic nitrogen donor ligands (N−N) bis(1-methylimidazol-2-yl)methane (bim) and bis(1-pyrazolyl)methane (bpm), are efficient catalysts for hydroamination. The cyclization of an aliphatic aminoalkyne to the corresponding five-membered imine heterocycle was achieved in good yield with excellent regioselectivity using both rhodium and iridium catalysts. The nature of the counterion to the cationic catalysts has a significant effect on the rate of the hydroamination reaction and interionic contacts between the metal complexes and their counterions in solution were clearly visible by NMR spectroscopy using the nuclear Overhauser effect, indicating a strong anion/cation interaction in solution. The nature of the coligands also had a significant effect on the efficiency of the metal complexes as catalysts, and complexes containing phosphine coligands were less effective catalysts compared to those complexes containing CO coligands. The X-ray crystal structure of the new iridium(I) complex [Ir(bim)(CO)2]+[BPh4]- (2) is reported, as well as the synthesis and characterization of the Rh complex [Rh(bpm)(CO)2]+[BPh4]- (3).

Formation and molecular structure of novel Ru(III) dimers of a symmetric antitumor drug analogue

The symmetrical anionic and neutral dimers [H(TMSO) 2] 2 trans-[{RuCl 4(TMSO)} 2](μ-pyz) ( 1), and mer-[{RuCl 3(TMSO) 2} 2](μ-pyz) ( 2) were isolated by the reaction of [H(TMSO)] trans-[RuCl 4(TMSO) 2] and mer-[RuCl 3(TMSO) 3] with heterocyclic nitrogen donor ligand pyrazine (pyz) at room temperature. These complexes can be regarded as unprecedented examples in the general Creutz-Taube family of ruthenium dimers. Each ruthenium center in 1 and 2 has a coordination environment akin to that of known anionic and neutral monomeric Ru(III) complexes. Crystals of 1 · acetone are orange, needle like, space group P 1 ̄ , a=10.419(3) Å, b=10.539(3) Å, c=12.595(5) Å, α=69.837(16)°, β=69.968(15)°, γ=74.330(15)° and crystals of 2 · 4TMSO are orange prisms, trigonal, space group R 3 ̄ , a=33.971(5) Å, b=33.971(5) Å, c=12.210(2) Å, α=90°, β=90° and γ=120°.

Synthesis and structure of some cobalt(III) complexes with azide, dimethylglyoxime and heterocyclic nitrogen donor ligands

A series of new hydrogen bonded trans-azidocobaloxime of the type [Co(DH) 2 N 3 L] where DH = dimethylglyoximato anion, L = [pyridine, piperidine, piperazine, quinoline, iso-quinoline, triazole, indole, benzimidazole, benzotriazole, or carbazole] have been prepared by passing air in cobalt(II) acetate, sodium azide, dimethylglyoxime and heterocyclic nitrogen donor ligands in ethanol medium. The complexes are characterized by UV, IR, NMR spectra. The thermogravimetric analyses indicate that these compounds are quite stable upto 200 and never associated with solvent or water molecules.