Homoleptic palladium complexes with phosphine-amide or iminophosphine ligands

The reaction between Pd(dba)₂ and phosphino-amide ligands yielded the unexpected Pd(II) homoleptic complexes [Pd(o-Ph₂PC₆H₄CO-NR)₂] [R = ⁱPr (1), Ph (2), 4-MeC₆H₄ (3), 4-FC₆H₄ (4)], in which an κ²-P,N coordination mode for diphenylphosphine-benzamidate ligands is observed. In order to induce amide protonation in the ligands and subsequent κ²-P,O coordination, compounds (1-4) were treated with HClO₄(aq) to give cationic complexes [Pd(o-Ph₂PC₆H₄CO-NHR)₂][ClO₄]₂ (5-8). These complexes and the analogous with iminophosphine ligands [Pd(o-Ph₂PC₆H₄CHN-R)₂] [ClO₄]₂ [R = ⁱPr (9), Ph (10)] can be alternatively obtained when [PdCl₂(PhCN)₂] is treated with AgClO₄ in the presence of the corresponding ligand. The reaction of Pd(dba)₂ with iminophosphines has also been explored, yielding in this case the Pd(0) derivatives [Pd(o-Ph₂PC₆H₄CHN-R)₂] [R = ⁱPr (11), Ph (12)]. X-ray structures of (3), (4), (5), (8) and (9) have been established, allowing an interesting comparative structural discussion.     

Copper complexes with bioactive ligands

Biological properties of new copper(II) complexes of 2-methylthionicotinate (2-MeSNic) of composition Cu(2-MeSNic)₂(MeNia)₂·4H₂O (where MeNia isN-methylnicotinamide), Cu(2-MeSNic)₂(Nia)₂·2H₂O (where Nia is nicotinamide) and Cu(2-MeSNic)₂(₂ (where L is isonicotinamide (iNia) or ethyl nicotinate (EtNic)) are reported. Gram⁻-bacteria (Escherichia coli) are more resistant against Cu(II) complexes than Gram⁺-bacteria (Staphylococcus aureus)—significant antistaphylococcal activity was found with Cu(2-MeSNic)₂(MeNia)₂·4H₂O (IC₅₀ 1.3 mmol/L).Caddida parapsilosis was most inhibited by Cu(2-MeSNic)₂·H₂O and Cu(2-MeSNic)₂(MeNia)₂·4H₂O (IC₅₀ 1.4 mmol/L and 1.5 mmol/L, respectively). Biosynthesis of nucleic acids influenced by Cu(2-MeSNic)₂-(Nia)₂·2H₂O indicated by incorporation of¹⁴C-adenine (IC_50(Ade) 0.31 mmol/L) is more sensitive than biosynthesis of proteins indicated by incorporation of¹⁴C-leucine (IC_50(Leu) 9.94 mmol/L). Cu(II) complexes with expressed antimicrobial activity showed no mutagenic activity.     

Dimolybdenum complexes with mixed formamidinate ligands

A series of dimolybdenum complexes containing mixed formamidinate ligand are discussed. The reactions of trans-Mo₂(O₂CCH₃)₂(o-DMophF)₂ [o-HDMophF=N,N^′-di(2-methoxyphenyl)formamidine] with N,N^′-di(2-pyridyl)formamidine (HDpyF), N,N^′-di(2-pyrimidyl)formamidine (HDpmF) and N,N^′-di(6-methyl-2-pyridyl)formamidine (HDMepyF), in refluxing CH₂Cl₂ afforded the complexes, trans-Mo₂(O₂CCH₃)(DpyF)(o-DMophF)₂ (1), trans-Mo₂(O₂CCH₃)(DpmF)(o-DMophF)₂ (2), and trans-Mo₂(O₂CCH₃)(DMepyF)(o-DMophF)₂ (3), respectively. The o-DMophF⁻ and DMepyF⁻ ligands in these complexes adopt the s-cis, s-trans conformation, resulting in Mo-O short distances [2.889 (3) and 2.861(2) Å for 1; 2.880(3) and 3.024(4) Å for 2], while the DpyF⁻ ligand adopts the s-cis, s-trans conformation, resulting in a Mo-N [3.208(4) Å] and a Mo-H [2.90 (3) Å] short distances. The reactions of trans-Mo₂(O₂CCH₃)₂(o-DMophF)₂ with HDMepyF in CH₃CN gave complexes 3, trans-Mo₂(O₂CCH₃)(DMepyF)₂(o-DMophF) (4), and trans-Mo₂(DMepyF)₂(o-DMophF)₂ (5). The o-DMophF⁻ ligands in 4 and 5 adopt the s-cis, s-cis conformation while DMepyF⁻ assumes an s-cis, s-trans conformation. Complexes 1-5 are the first dimolybdenum complexes containing mixed formamidinate ligands.     

Transition metal complexes with pyrazole derivatives as ligands

Degradation reactions of scorpionates were observed in the presence of transition metal salts MX₂ to give complexes of transition metal and pyrazole derivatives. Otherwise, pyrazolato complexes of transition metals and weakly coordinating anions such as nitrates have been synthesized from transition metal nitrates and 3-phenyl- and 4-phenyldiazo-pyrazole. A number of complexes with pyrazole derivatives as ligands, [Zn(3-tBupzH)₂Cl₂], [Fe₂(3-Phpz)₆Cl₄], [Cu(pzH)₄Br₂], [Ni(py)₂(pzH)₂Cl₂], [Li(THF)₄][Ti₂(μ-pz)₃Cl₄(NMe₂)₂], [Zn₂(μ-3-Phpz)₂(3-PhpzH)₂][(NO₃)₂], [M(3-PhpzH)₄(NO₃)₂] (M = Co, Ni, Cu, Zn, Cd), [Zn(3-PhpzH)₂(NO₃)₂], [Zn(4-PhNNpzH)₂(NO₃)₂](H₂O), and [Cd(4-PhNNpzH)₂(NO₃)₂(H₂O)₂], have been crystallized and characterized by single-crystal X-ray diffraction.     

Crystal structure of amylose complexes with small ligands

Amylose complexes were prepared, as lamellar single crystals and polycrystalline powders, from aqueous solutions by adding small flavor molecules. The morphology, crystal structure, and thermal properties of complexes with fenchone, menthone, and geraniol were determined using transmission electron microscopy, wide-angle X-ray diffraction, and differential scanning calorimetry. The crystal structure was found to be similar to that of V amylose complexes with isopropanol. This implies that the crystallosolvates contain sixfold helices packed in orthorhombic unit cells, with the ligands possibly lying in the interhelical space. Different drying procedures were also studied leading to less resolved X-ray diagrams. The thermoanalysis confirmed that complexes with a relatively high crystallinity were formed.     

Platinum(IV) chloride complexes with heterocyclic ligands

Platinum(IV) chloride complexes with heterocyclic ligands have been prepared and characterized by infrared and electronic spectra. The compounds are of general formula Pt(L)nCl4, where L = N-ethylimidazole, N-propylimidazole, isoxazole, 3,5-dimethylisoxazole, benzoxazole, 2-methylbenzoxazole, 2,5-dimethylbenzoxazole, ethylenediamine, n = 2, 4, and also Pt(enEt2)3Cl4 X 2H2O, where enEt2 = N,N-diethylethylenediamine. These complexes are hexacoordinate with cis or trans configuration. The antitumoral activity of some complexes in mice inoculated with leukemia L1210 is reported.     

Di-organocobalt complexes of macrocyclic ligands

Three new di-metallorganic cobalt complexes of the type trans-(Bz)₂Co(chel), where Bz is a benzyl group σ-bonded to cobalt atom and chel is an equatorial chelating system constituted by an amino-oximic ligand and its conjugated base, were synthesised. The protonated and the unprotonated ligands interact through an O-H ? O bridge stabilising the entire structure. The complexes differ in the equatorial moiety which is derived from the following ligands: HLN-py=3-[(2-pyridyl)ethylimino]-butan-2-one oxime), HLN-Ph=3-[(2-phenyl)ethylimino]-butan-2-one oxime and the analogous HLN-PhCl=3-[(2-chlorophenyl)ethylimino]-butan-2-one oxime. Two of these compounds, namely those derived from HLN-py and HLN-PhCl were structurally characterised by means X-ray diffractometry. Data reveal that each complex is characterised by the presence of two unusually long cobalt-carbon bonds which are 2.120(4) Å (mean value) in complex with HLN-py ligand and 2.119(4) Å (mean value) in complex with HLN-PhCl. These data are consistent with a strong mutual trans-influence exerted by one ligand on the other.     

Structural studies of lanthanide complexes with tetradentate nitrogen ligands

Complexes have been synthesised with bis(2-pyridine carboxaldehyde) ethylenediimine (1) and bis(2-pyridine carboxaldehyde)propylene-1,3-diimine (2) with all of the available lanthanide trinitrates. Crystal structures were obtained for all but one complex with 1 and for all but one complex with 2. Four distinct structural types were established for 1 but only two for 2, although in all cases the structures contained one ligand bound to the metal in a tetradentate fashion. With 1, the four different structures of the lanthanide(III) nitrate complexes included 11-coordinate [Ln(1)(NO₃)₃(H₂O)] for Ln = La; 10 coordinate [Ln(1)(NO₃)₃(H₂O)] with one monodentate and two bidentate nitrates for Ln = Ce, then 10-coordinate [Ln(1)(NO₃)₃] for Ln = Pr-Yb with three bidentate nitrates; and 9-coordinate [Ln(1)(NO₃)₃] with one monodentate and two bidentate nitrates for Ln = Lu. On the other hand for 2 only two distinct types of structure are obtained, the first type with Ln = La-Pr and the second type for Ln = Sm-Lu, although all are 10-coordinate with stoichiometry [Ln(2)(NO₃)₃]. The difference between the two types is in the disposition of the ligand relative to the nitrates. With the larger lanthanides La-Pr the ligand is found on one side of the coordination sphere with the three nitrate anions on the other. In these structures, the ligand is folded such that the angle between the two pyridine rings approaches 90°, while with the smaller lanthanides Sm-Lu, two nitrates are found on one side of the ligand and one nitrate on the other and the ligand is in an extended conformation such that the two pyridine rings are close to being coplanar. In both series of structures, the Ln-N and Ln-O bond lengths were consistent with the lanthanide contraction though there are significant variations between ostensibly equivalent bonds which are indicative of intramolecular hydrogen bonding and steric crowding in the complexes.     

Luminescence properties of cyclopalladated complexes with Schiff base ligands

Direct reaction between the hydroxo-complexes [{Pd(μ-OH)(C^N)}₂] (C^N = 2-(2-pyridyl)phenyl (Phpy) I; C^N = 7,8-benzoquinolyl (Bzq) II) and N-naphtylsalycilaldimine (N-naphsal) 1 yields new mononuclear cyclometallated palladium(II) complexes [Pd(N-naphsal)(C^N)] (I1, II1). Photophysical properties were investigated together with those of complexes with related ligands N-phenylsalycilaldiminate (N-Phsal) 2, N-p-chlorophenylsalycilaldiminate (N-pClPhsal) 3. All the compounds absorb intensely below 300 nm via¹LC transitions located in Bzq or Phpy ligands, and display additional low energy absorptions of mixed ¹MLCT-¹LC character. The complexes under study are quite unusual in terms of luminescence behavior, since some of them are emissive in solution at room temperature and all display intense emissions in frozen CHCl₃ solution, but also in solid state at 298 and 77 K. Structural characterization by X-ray diffraction of complexes I2, I3 and II2 confirmed the proposed formulae.     

Synthesis of some ruthenium complexes with mixed diimine ligands

The use of Ru(DMSO)₄Cl₂ and Ru(PY)₄Cl₂ (DMSO=dimethyl sulphoxide; Py=pyridine) in synthesizing mixed ligand complexes is reported. The bidentate ligands used are of the diimine type, namely, 2,2′-bipyrimidine (bpm); 3,6-di-(2-pyridyl)-1,2,4, 5-tetrazine (dpt); 2,3-bis(2-pyridyl)-5,6-dihydropyrazine (dhp); 2,3-bis(2-pyridyl)-pyrazine (dpp); 2,3-bis-(2-pyridyl)-quinoxaline (dpq); 2,3,5,6-tetrakis(2-pyridyl)-pyrazine (tpp). Characterization of the complexes has been accomplished using elemental analysis, conductivity, IR and UV-Vis spectroscopy.     

Copper complexes with bioactive ligands. Part II--Antifungal activity

Antifungal activity of new copper(II) complexes of 2-methylthionicotinate (2-MeSNic) of the composition Cu(2-MeSNic)₂(MeNia)₂·4H₂O (where MeNia isN-methylnicotinamide), and Cu(2-MeSNic)₂(Nia)₂·2H₂O (where Nia is nicotinamide) and Cu(2-MeSNic)₂L₂ (where L is isonicotinamide, iNia, or ethyl nicotinate, EtNic) were tested on various strains of filamentous fungi by the macrodilution method. Most sensitive against copper(II) adducts with bioactive ligands wereRhizopus oryzae andMicrosporum gypseum (IC₅₀ 1.5–2.3 mmol/L). The adducts with Nia, MeNia and EtNic at 5 mmol/L induced morphological changes in growing hyphae ofBotrytis cinerea, mainly their intensive branching attached to release of cytoplasm with partial growth inhibition. Inhibition of sporulation (>90%) ofAlternaria alternata by Cu(2-MeSNic)₂·H₂O was observed as a change in the color of the colonies. The highest resistance was marked byB. cinerea andFusarium moniliforme (average IC₅₀ values 4.25 and 3.13 mmol/L, respectively). The presence of all bioactive ligands in copper(II) complexes caused an increase in the inhibition effect against model fungi (except significant inhibition activity of EtNic onR. oryzae). Part I: Copper complexes with bioactive ligands. Antimicrobial activity.Folia Microbiol.46, 379–384 (2001).     

Dinitrosyl iron complexes with thiol-containing ligands in plant tissues

The formation of dinitrosyl iron complexes with thiol-containing ligands in plant tissues (parsley and apple leaves) in the presence of nitric monoxide was demonstrated using electron paramagnetic resonance. In two types of tissues dinitrosyl iron complexes are predominantly represented by the binuclear diamagnetic form. This diamagnetic form can be transformed in EPR-detectable mononitrosyl iron complexes with diethyldithiocarbamate due to the ability of diethyldithiocarbamate to accept the iron-mononitrosyl groups from iron-dinitrosyl fragments of binuclear complexes. A similar transformation was observed under the effect of diethyldithiocarbamate on a mononuclear paramagnetic form of dinitrosyl iron complexes. The significant amount of binuclear dinitrosyl iron complexes found in plant tissues suggests that these complexes can be considered as a “working form” of nitric monoxide, which is recognized now as a universal regulator of metabolic processes in plants as well as in other organisms.     

Zinc enzyme modelling with zinc complexes of polar pyrazolylborate ligands

The Zn-OH₂ and Zn-OH complexes of the new tris(pyrazolyl)borate ligands with pyridyl and carboxamido substituents were investigated for their reactivity towards hydrolyzeable substrates. Tp^4−Py,MeZn-OH inserted CO₂ and CS₂ in methanol forming the Zn-OCOOMe and Zn-SCSOMe products. In non-aqueous media, both types of complexes with both types of substituents on the Tp ligands effected stoichiometric cleavage of tris(p-nitrophenyl)phosphate and p-nitrophenyl acetate. In solutions containing water and the MOPS buffer, up to eight p-nitrophenyl groups per equivalent of zinc complex could be cleaved from the esters, and the resulting bis(p-nitrophenyl)phosphate was also degraded to mono(p-nitrophenyl)phosphate. This is the first time that pyrazolylborate-zinc complexes have shown catalytic activity in hydrolytic reactions.     

Structure and electronic properties of heme complexes with various ligands

The electronic and atomic structures, and the molecular dynamics of the atomic structure at 310 K of a set of heme complexes with His and Gly amino acids in the 5th coordination position and some ligands (O2, NO) in the 6th position were studied by ab initio (3-21G basis set) and semiempirical (PM3) quantum chemistry methods and the method of molecular dynamics. It was shown that the type of coordination of the imidazole ring influences the constant of chemical bonding of molecular oxygen of the complexes. On the other hand, NO and O2 molecules have different transinfluence on the ligand in the 5th coordination position. It was shown that temperature affects profoundly the atomic and electronic structures of the complexes, the tightness of chemical bonding and their reactivity.     

Half-sandwich Mo(III) complexes with asymmetric diazadiene ligands

The asymmetric 1,4-diazadiene ligands R^∗NCHCHNR^∗ [R^∗ = (S)-CH(CH₃)Ph], , and 2,2′-bis(4-ethyloxazoline), as-ox, have been used to generate half-sandwich Mo^III derivatives by addition to Cp₂Mo₂Cl₄. Ligand affords a mononuclear, paramagnetic 17-electron product, , whereas as-ox leads to the isolation of a dinuclear compound where only one molecule of ligand has been added per two Mo atoms, Cp₂Mo₂Cl₄(as-ox). In the presence of free as-ox, this compound coexists with the paramagnetic mononuclear complex in solution. Both products are capable of controlling the radical polymerization of styrene under typical atom transfer radical polymerization (ATRP) conditions. However, the tacticity of the resulting polystyrene does not differ from that given by conventional free radical polymerization.     

Metal binding to ligands: cadmium complexes with glutathione revisited

We studied the interaction of gamma-L-glutamyl-L-cysteinyl-glycine (glutathione, GSH) with cadmium ions (Cd(2+)) by first performing classical potentiometric pH titration measurements and then turning to additional spectroscopic methods. To estimate the residual concentrations of free cadmium, we studied the competition of glutathione with a Cd(2+)-sensitive dye, either an absorbing dye (murexide) or a fluorescent one (FluoZin-1), and consistent results were obtained with the two dyes. In KCl-containing Tes, Mops, or Tris buffer at pH 7.0 to 7.1 and 37 degrees C (and at a total Cd(2+) concentration of 0.01 mM), results suggest that free cadmium concentration is halved when the concentration of glutathione is approximately 0.05 mM; this mainly reflects the combined apparent dissociation constant for the Cd(glutathione) 1:1 complex under these conditions. To identify the other complexes formed, we used far-UV spectroscopy of the ligand-to-metal charge transfer absorption bands. The Cd(glutathione)(2) 1:2 complex predominated over the 1:1 complex only at high millimolar concentrations of total glutathione and not at low submillimolar concentrations of total glutathione. The apparent conditional constants derived from these spectroscopy results made it possible to discriminate between sets of absolute constants that would otherwise have simulated the pH titration data similarly well in this complicated system. Related experiments showed that although the Cl(-) ions in our media competed (modestly) with glutathione for binding to Cd(2+), the buffers we had chosen did not bind Cd(2+) significantly under our conditions. Our experiments also revealed that Cd(2+) may be adsorbed onto quartz or glass vessel walls, reducing the accuracy of theoretical predictions of the concentrations of species in solution. Lastly, the experiments confirmed the rapid kinetics of formation and dissociation of the UV-absorbing Cd(glutathione)(2) 1:2 complexes. The methods described here may be useful for biochemists needing to determine conditional binding constants for charge transfer metal-ligand complexes under their own conditions.     

New four- and five-coordinated complexes of cobalt with sterically hindered o-iminobenzoquinone ligands: synthesis and structure

New square planar Co^II(ISQ-iPr)₂ (1), Co^II(ISQ-Me)₂ (2) and five-coordinate Co^III(ISQ-Me)₂Cl cobalt complexes (3) (ISQ-iPr=4,6-di-tert-butyl-N-(2,6-di-iso-propylphenyl)-o-iminobenzosemiquinonate radical-anion, ISQ-Me=4,6-di-tert-butyl-N-(2,6-di-methylphenyl)-o-iminobenzosemiquinonate radical-anion) have been prepared using different methods. Complexes 1-3 have been characterized by IR, UV-Vis, EPR spectroscopy. Molecular structures of 1 and 3 were determined using X-ray crystallography. It has been established from variable-temperature magnetic susceptibility measurements and X-band EPR spectroscopy that 1 and 2 possess an S=1/2 ground state. In the complex molecules the unpaired electrons of o-iminobenzosemiquinonate radical ligands (S_rad=1/2) are strongly coupled antiferromagnetically. The sterical hindrances of N-aryl in o-iminobenzosemiquinonate ligands prevent the formation of a hexacoordinate species.     

New Fe starting materials: preparation, characterisation and structural features of iron halide complexes with alcohol ligands

The new mononuclear [FeCl₂(HOPrⁱ)₄] (1), polymeric [{Cl₃Fe(μ-Cl)Fe(HOPrⁱ)₄}_n] (2) and binuclear [I₂Fe(μ-I)₂Fe(PrⁱOH)₄] (3) iron(II) complexes have been synthesized in high yields in propan-2-ol or toluene/propan-2-ol mixtures at room temperature. Magnetic moment measurements, ⁵⁷Fe Mössbauer spectroscopy data and the results of semi-empirical quantum mechanical calculations confirmed the high-spin configuration of the iron(II) centres, which were shown to be four- and/or six-coordinate by single crystal X-ray diffraction analyses. Intermolecular hydrogen bonding was observed in the solid state structure of 1, intramolecular interactions in 2, while both intra- and intermolecular association was seen in 3. Long iron-(μ-halide) bonds suggest the possibility of complex dissociation in solution and facile ligand substitution in 2 and 3.