A new class of ruthenium complexes containing Schiff base ligands as promising catalysts for atom transfer radical polymerization and ring opening metathesis polymerization

A novel series of Schiff base ruthenium complexes that are active catalysts in the field of atom transfer radical polymerization (ATRP), have been prepared. Moreover, when activated with trimethylsilyldiazomethane (TMSD), these species exhibit good catalytic activity in the ring opening metathesis polymerization (ROMP) of norbornene and cyclooctene. The activity for both the ROMP and ATRP reaction is dependent on the steric bulk and electron donating ability of the Schiff base ligand. The control over polymerization in ATRP was verified for the two substrates that exhibit the highest activity, namely MMA and styrene. The results show that the optimal ATRP equilibrium leading to a controlled polymerization, can be established by adjusting the steric and electronic properties of the Schiff base ligand.     

Coordination of nitrogen-containing ligands by Co complexes with tetra-and dodeca-substituted porphyrins

Capabilities of complexes with tetraphenylporphyrin, the derivative of tetrapyridiniumporphyrin, and with β-octabromine-meso-tetraphenylporphyrin to coordinate additional nitrogen-containing ligands are compared. The equilibrium constants of addition of extra ligands, namely, pyridine, piperidine, and N-methylimidazole, to the Co complexes with these porphyrins in ethanol solutions at 298 K are determined.     

Tertiary-poly-amine ligands as stabilisers of transition metal complexes with uncommon oxidation states

Abstract

Tertiary-amine ligands are known to be poorer [sgrave] donor ligands than the corresponding primary- or secondary-amine ligands. They are known to shift the redox potentials of given couples to the anodic direction relative to the corresponding complexes with primary- or secondary-amine ligands. A review of data in the literature and of recent results on nickel complexes with tetra-aza-macrocyclic ligands and copper complexes with open chain polyamine ligands suggests that the major source for these effects is the poorer solvation of the complexes with the tertiary-amine complexes due to the lack of hydrogen bonding between the complexes and the solvent, or the counter ions. Thus the stabilisation of low valent transition metal complexes by tertiary-amine ligands is due to thermodynamic reasons. On the other hand, tertiary-amine-macrocyclic ligands stabilise high valent complexes because the route to the formation of imine groups is kinetically inhibited in these complexes.     

Nitrosubstituted hydroxamate ligands in new triphenyltin(IV) complexes as prospective antimicrobial agents

New triphenyltin(IV) hydroxamate complexes, [Ph₃Sn(4-NO₂CnH)] and [Ph₃Sn(4-NO₂BzH)] have been synthesized by the reactions of Ph₃SnCl with potassium 4-nitrocinnamo hydroxamate [4-NO₂C₆H₄CHCHCONHOK] (KHL¹) and potassium 4-nitro benzohydroxamate [4-NO₂C₆H4CONHOK] (KHL²). The complexes were synthesized in 1:1 molar ratio in MeOH?+?C₆H₆ and characterized by physicochemical and IR, ¹H NMR, and mass spectrometry. The bidentate hydroxamate involving bonding through carbonyl and hydroxamic oxygen (O, O coordination) has been inferred from IR spectra. The electrochemical behavior of complexes has been analyzed. Quasi-irreversible two electron metal-centered cathodic process of type Sn^IV/Sn^II redox couple was indicated by cyclic voltammetric technique. The thermal behavior of 1 and 2 studied by TGA has shown continuous decomposition to yield Sn + 0.5SnO₂ and SnO₂ as final residues. The in vitro antimicrobial activity assays of 1 and 2 against pathogenic Gram-positive bacteria (Bacillus subtilis and Staphylococcus aureus), Gram-negative bacteria (Salmonella typhi and Pseudomonas aeruginosa), and fungi (Aspergillus fumigatus and Alternaria alternata) were done by MIC method. The complexes have exhibited appreciable antimicrobial activity relative to the respective standard Gentamycin and Nystatin drugs.     

Dinitrogen complexes of iron(II) with chelating agents as ligands

Two new dinitrogen compounds of formulae Na₂[Fe(EDTA)N₂].2H₂O and Na₂[Fe(CDTA)N₂].2H₂O have been synthesized from [Fe(H-EDTA)H₂O] and [Fe(H-CDTA)-H₂O], respectively, and NaN₃. Both complexes have been characterized by IR and electronic spectra. The thermal behaviour has been studied by TG and DTA techniques.     

Dioxygen evolution from aqueous acid solutions of ruthenium complexes with nitrogen-containing ligands

Some peculiarities of reduction of one-electron oxidants, Ru(bpy) ₃ ³⁺ and Ru(bpy)₂(py) ₂ ³⁺ , in the absence of catalysts (when oxidation of the oxidant's ligands occurs) and in their presence (when also oxidation of water to dioxygen occurs) are discussed. Both oxidation reactions are thought to have a common intermediate.

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Ru(bpy) ₃ ³⁺ Ru(bpy)₂(py) ₂ ³⁺ ( -) ( ). , .

     

1,2,4-Thiadiazoles as promising multifunctional agents for treatment of neurodegenerative diseases

Detailed studies of properties of new 3-substituted 5-anilino-1,2,4-thiadiazoles containing different substituents at position 3 of the thiadiazole ring were carried out, in particular, their esterase profile and antioxidant properties. It was found that the presence in the molecule of 2-aminopropyl fragment determines an efficient and selective inhibition of butyrylcholinesterase as compared to acetylcholinesterase and carboxylesterase, with radical-scavenging activity being weak. The compounds containing a 2-aminopropenyl fragment possess a high radicalscavenging activity, weakly inhibit cholinesterases, and exhibit anticarboxylesterase activity. A wide spectrum of activity of 3-substituted 5-anilino-1,2,4-thiadiazoles as inhibitors of cholinesterases and highly efficient scavengers of free radicals gives a basis for the optimization of structure and development in this series of original agents for therapy of neurodegenerative diseases.     

Thioketone spin traps as mediating agents for free radical polymerization processes

Thioketones are demonstrated to be suitable agents for controlling free radical polymerization processes: the polymerizations carry (pseudo) living characteristics indicating that the control process is induced by a persistent radical effect.     

Ru-TAP complexes with btz and pytz ligands: novel candidates as photooxidizing agents

Two ligands containing 1,2,3-triazole moieties 1 and 3 were easily prepared by a Cu(I)-catalysed "click reaction" between commercially available (trimethylsilyl)alkynes and benzyl azide. These ligands were used in the synthesis of Ru(II) complexes with TAP ligands, i.e. [Ru(TAP)(2)btz](2+)2 and [Ru(TAP)(2)pytz](2+)4. The electrochemical and photophysical properties of these complexes were investigated. The data show that both complexes should behave as highly oxidizing agents under illumination. However, complex 4 displays more attractive photophysical properties than complex 2 and constitutes thus a Ru-TAP compound that can be easily derivatized for photodamaging biomolecules.     

Highly cytotoxic iron(II) complexes with pentadentate pyridyl ligands as a new class of anti-tumor agents

The iron(II) complexes and with pentadentate pyridyl ligands are stable under physiological conditions and exhibit higher cytotoxicities toward a series of human carcinoma cell lines than cisplatin; can significantly increase intracellular oxidant levels, cleave supercoiled plasmid DNA in vitro without addition of a reductant and induce apoptotic cell death in human cervical epithelioid carcinoma cells (HeLa) as observed in flow cytometric studies.     

A promising method for phosphinidene generation: complexes of phosphinidenes with N-donor ligands

1,3,2-diazaphospholenes and related compounds can formally be regarded as complexes of phosphinidenes (R-P) with 1,4-diazabutadienes. The dissociation Gibbs free energies of these "complexes" were calculated by using density functional theory (B3LYP/3-21G(*) and B3LYP/6-311+G**). The dissociation Gibbs free energies show systematic dependence on the phosphorus substituent as well as on the stability of the N-donor ligand formed as a byproduct. The thermodynamics and kinetics of the dissociations were thoroughly examined. The results allow us to conclude that novel routes of phosphinidene generation can be developed.     

Triethylenetetramine penta- and hexa-acetamide ligands and their ytterbium complexes as paraCEST contrast agents for MRI

The ligand triethylenetetramine-N,N,N',N',N',N'-hexaacetamide (ttham) was synthesized with the aim of forming lanthanide complexes suitable as contrast agents for magnetic resonance imaging applications utilizing the chemical exchange-dependent saturation transfer (CEST) effect. It was designed to exclude water molecules from the first coordination sphere and provide a high number of CEST active amide protons per lanthanide ion. The ligand was characterized by its protonation behavior and its complexation properties with ytterbium ions in aqueous solution. The basicity of the ttham backbone amine protons decreases in the order N(central(1)) > N(terminal(1)) > N(terminal(2)) > N(central(2)), as deduced from NMR titration experiments and from a comparison of its protonation constants with those of two ttham derivatives, in which either a terminal (N-benzyl-triethylenetetramine-N,N',N',N',N'-pentaacetamide, 1bttpam) or a central acetamide group (N'-benzyl-triethylenetetramine-N,N,N',N',N'-pentaacetamide, 4bttpam) is substituted with a benzyl group. This protonation sequence results from the combined influence of inductive effects, the intramolecular hydrogen bonding network, and the Coulomb repulsion between protonated ammonium groups. The ytterbium complex of ttham, [Yb(ttham)]Cl(3), is coordinatively frustrated. Due to steric constraints, in addition to the four backbone nitrogen atoms, only three of the four symmetry-equivalent terminal acetamide donors can coordinate simultaneously to the ytterbium ion, and the dangling fourth one exchanges quickly with the other three. The ytterbium complexes of a total of five ligands (ttham, 1bttpam, 4bttpam, 2,2',2'-triaminotriethylaminehexaacetamide (ttaham), and diethylenetriamine-N,N,N',N',N'-pentaacetamide (dtpam)) were studied with respect to their CEST properties. In solution, all of these complexes have a low symmetry. The presence of multiple magnetically different amide groups in each complex prevents the realization of very high CEST effects. These results nevertheless form an excellent basis for a further optimization of this class of ligands.     

Perspectives for thiamin as a preparation for correction of free radical states of different origin

Аntioxidant capacity of thiamin has been investigated, Liposome suspension being the standard biological test-system has been used for this purpose Antioxidant capacity of thiamin has been investigated. Liposome suspension being the standard biological test-system has been used for this purpose. Thiamin usually being not included in the list of antioxidant substances is able to interfere the processes of lipid peroxidation. Such effects give the possibility to extend the scale of thiamine practical application and to recommend it for correction different free radical states including environmentally induced free radical diseases.     

Reactivity of allylphosphines with iridium complexes: Diallylphosphines as new bidentate ligands

Addition of four equivalents of t-butyldiallylphosphine 1a to a solution of one equivalent of [(COE)₂IrCl]₂ in CHCl₃ at low temperature produced two isomers of thecomplex [t-Bu(C₃H₅)PCH₂CH=CH)]IrHCl(COE)-[PtBu(C₃H₅)₂] ( 2a ), which evolve at 40°C to [t-Bu(C₃H₅)PCH₂CH=CH)]IrCl(C₈H₁₅)[PtBu(C₃H₅)₂] ( 3a ), by a hydride transfer from iridium to the cyclooctene (COE) ligand. It is reasonable that the unsaturation at the iridium center is fulfilled by interactions with the allyl moieties of the phosphine that are not metalated. This has been demonstrated by bubbling CO into a solution of 3a in CHCl₃ at room temperature to obtain the carbonyl complex [t-Bu(C₃H₅)-PCH₂CH=CH)]Ir(CO)Cl(C₈H₁₅)[PtBu(C₃H₅)₂] ( 4a ). Under the same conditions, the reaction of diisopropylamindiallylphosphine 1b and anisyldiallylphosphine 1c afforded a mixture of isomers 3b and 3c , respectively. These results show that diallylphosphines can be considered to be a new family of bidentate ligands. Finally, the reaction of these phosphines with [(COD)IrCl]₂ (COD = 1,5 cyclooctadiene) shows the formation of tetracoordinated iridium (I) complexes IrCl(COD)(PR3), which are thermally stable. © 1998 John Wiley & Sons, Inc. Heteroatom Chem 9:253–259, 1998     

Carborane complexes of ruthenium with long-chain diphosphine ligands as effective catalysts of controlled radical polymerization

Catalytic systems based on carborane complexes of ruthenium with long-chain diphosphine ligands, such as 1,4-bis(diphenylphosphino)butane and 1,5-bis(diphenylphosphino)pentane, are prepared for the controlled radical polymerization of methyl methacrylate. It is found that the used metallacarboranes can catalyze polymerization initiated by both carbon tetrachloride and 2,2′-azo-bis(isobutyronitrile). It is shown that closo-ruthenacarborane with 1,5-bis(diphenylphosphino)pentane 3,3-[PPh₂(CH₂)₅PPh₂]-3-Cl-3,1,2-closo-RuC₂B₉H₁₁ and its o-phenylenecycloborated derivatives make it possible to conduct polymerization at higher rates than those attained with the use of previously synthesized complexes based on diphosphines with a smaller length of the hydrocarbon fragment. The relationship between the redox potential of the complex and the efficiency of control over molecular-mass characteristics of the polymers is analyzed. Experiments reveal that the addition of small amounts of aliphatic amines causes a considerable increase in the rate of polymerization and leads to a decrease in the concentration of the catalyst with retention of a high degree of control over the process.     

Cisplatin cyclodextrin complexes as potential free radical chemoradiosensitizers for enhanced cisplatin treatment of cancers: a quantum mechanical study

It has been shown in this study that {CisPt@[n]CD} complexes formed from the anti-cancer drug cisplatin (CisPt) and cyclodextrins ([n]CD) can be a source of Pt based free radicals such as (H₃N)₂PtCl· and (H₃N)₂Pt·· species in water within a radiation environment which can produce hydrated electrons. Encapsulating CisPt within the [n]CD host takes advantage of the previously described drug delivery and reduced side effect advantages of CDs. Based on quantum mechanical modelling and literature results from other studies, it is predicted that {CisPt@[γ]CD} and the analogous 2-hydroxypropyl[β]cyclodextrin (HPBCD) complex {CisPt@HPBCD} may interact with serum albumin and engage in an enhanced permeation and retention mechanism in solid tumours, offering further synergistic advantages for radiation-{CisPt@[γ]CD} or -{CisPt@HPBCD} regimens over that of the conventional radiation-CisPt regimens in current use in anti-cancer chemoradiotherapies. Comparisons and possible advantages are made with the previously documented chemoradiosensitizing properties of the analogous cucurbit[7]uril based{CisPt@[7]CB} complex with the {CisPt@[γ]CD} and {CisPt@HPBCD} complexes suggest that all three complexes may have different and tailorable anti-tumour uses for a range of different chemotherapeutic environments or protocols.