Search

4 pages; International audience; The iron complex generated in situ from Fe(CF3SO3)2 and the new tridentate N ligand mpzbpy (mpzbpy stands for 6-(3,5-dimethylpyrazol-1-ylmethyl)-60-methyl-2,20-bipyridine) mediates the room temperature oxidation of cyclohexane to cyclohexanol and cyclohexanone, and the epoxidation of cyclooctene to cyclooctene oxide. X-ray diffraction studies of single crystals obtained by reaction of iron(II) triflate with mpzbpy in methanol in the presence of ascorbic acid reveals the formation of a dinuclear complex, namely [Fe2(mpzbpy)2(C2O4)(CF3SO3)2] (1), where two iron(II) ions are bridged by an oxalato dianion originating from the oxidative cleavage of ascorbic acid. Magnetic susceptibility measurements of 1 show that the two metallic centres are weakly antiferromagnetically coupled, with a J value of 1.74(1) cm1.

Iron(II) complexes obtained from tetradentate, rigid, linear N4 ligands have been investigated to appraise the influence of steric effects and the impact of trans-coordinated anions on the spin-transition behavior. As expected, the well-designed ligands embrace the metal center, resulting in octahedral iron(II) complexes where the basal plane is fully occupied by the pyridine/pyrazole N4 ligand, while anions or solvent molecules are exclusively axially coordinated. Precursor complexes, namely, [Fe(bpzbpy)(MeOH)2](BF4)2 (where bpzbpy symbolizes the ligand 6,6'-bis(N-pyrazolylmethyl)-2,2'-bipyridine) and [Fe(mbpzbpy)(MeOH)2](BF4)2 (where mbpzbpy symbolizes the ligand 6,6'-bis(3,5-dimethyl-N-pyrazolmethyl)-2,2'-bipyridine), have been used for the in situ preparation of a series of structural analogues via the exchange of the weakly coordinated trans methanol molecules by various anions, such as thiocyanate, selenocyanate, or dicyanamide. The magnetic properties of all seven iron(II) compounds thus obtained have been investigated. Two iron(II) complexes, i.e., [Fe(bpzbpy)(NCS)2] and [Fe(bpzbpy)(NCSe)2], exhibit gradual spin-crossover (SCO) properties typical of isolated mononuclear species with weak cooperative interaction. These two SCO materials have been studied by Mössbauer spectroscopy, and the light-induced excited spin state trapping effect has been investigated, revealing the possibility to induce the spin-transition both by temperature variation and by light irradiation. A correlation between steric/anion effect and SCO behavior is suggested.

Iron(II) and cobalt(II) complexes (7-15) based on new aldimine 2, 6-bis[(imino)methyl]pyridine (1, 2, 4, 6) and ketimine (2, 6-bis[(imino)ethyl]pyridine (3, 5) ligands with bulky chiral aliphatic or aromatic terminal groups have been prepared and characterized by 1H NMR, 13C NMR, IR-, mass spectroscopy (EI), and elemental analysis. The complex [CoCl2(BBoMP)]·1/2 CHCl3 (13) (BBoMP: 2, 6-bis{(R-(+)-(bornylimino)-methyl}pyridine) crystallizes in monoclinic space group P21 with cell dimensions: a = 7.6603(11) A, b = 28.3153(14) A, c = 13.537(2) A, V = 2908.1(6) A3, Z = 4. The coordination sphere around Co is distorted trigonal bipyramidal.

The meso - and rac -like isomers of bis{η 5 -(1-benzyl)indenyl}zirconium dichloride ( 5 ), bis{η 5 -(1- para -methoxybenzyl)indenyl}zirconium dichloride ( 6 ), bis{η 5 -(1- para -fluoro-benzyl)indenyl}zirconium dichloride ( 7 ) and bis{η 5 -(1-phenylethyl)indenyl}zirconium dichloride ( 8 ) were synthesized and isolated. Solid-state structures of meso - and rac -like 5 were determined by X-ray structure analysis. Polymerization properties of the methylaluminoxane (MAO) activated diastereomers of complexes 5 – 8 were studied in ethene polymerizations under different monomer concentrations. The rac -like isomer of 1-phenylethyl-substituted 8 /MAO showed significantly higher activity than the 1-benzyl substituted analogs 5 – 7 /MAO. In addition, rac - 8 /MAO behaves like a single center catalyst producing polyethene with narrow molar mass distribution (1.8–1.9), while diastereomers of 5 – 7 /MAO produce polymers with molar mass distributions varying from 2.7 up to 10.3. The rac and meso -like isomers of 5 – 7 /MAO have different response on the monomer concentration. Quantum chemical calculations suggest a strong interaction between the benzyl substituent and the electron deficient zirconium center. The phenyl metal coordination energies depend on the electronic properties of the para -substituent. In 8 /MAO, due to the ethyl spacer, the coordination does not have a significant role and therefore much higher activity and single center polymerization behavior is observed.

Four tetradentate nitrogen ligands, viz. dichloro{[N,N′-diphenyl-N,N′-di(quinoline-2-methyl)]-1,2-ethylene diamine} (1), {[N,N′-dioctyl-N,N′-di(quinoline-2-methyl)]-1,2-ethylene diamine} (2), {[N,N′-dibenzyl-N,N′-di(quinoline-2-methyl)]-1,2-ethylene diamine} (3), and (1R,2R)-(−)-N,N′-di(quinoline-2-methyl) di-iminocyclohexane (4), were investigated as novel complexing ligands in iron-mediated atom transfer radical polymerization (ATRP) of methyl methacrylate where ethyl-2-bromoisobutyrate was the initiator in o-xylene at 90 °C. With ligands 1 and 2 the experimental molecular weights increased gradually with monomer conversion. High to moderate conversions (87%, 43%) were obtained in relatively short times (90 min for 1 and 30 min for 2), which indicates an efficient catalyst system, but after these times a dramatic increase in viscosity of the polymerization medium led to loss of control. It is noteworthy that polymerization proceeded in a controlled manner with ligand 1, which has two rather bulky substituents on the N-atom. Such bulky ligands did not work for a copper-based system, where they led to excessive terminations or other side reactions. When the bulkiness of the substituents was significantly increased, as in ligand 3, a decrease in polymerization rate and loss of control occurred. Ligand 4 was less efficient than the other ligands, probably because the ethylene bridge was replaced by cyclohexane bridge.

Iron(II) dichloride complexes bearing a tridentate nitrogen donor ligand were investigated for the homopolymerization of tert-butyl acrylate after activation with methylaluminoxane. Two new complexes were synthesized, 2,6-bis[1-(cyclohexylimido)ethyl]pyridine iron chloride (FeCl2) and 2,6-bis[1-(isopropylimido)ethyl]pyridine FeCl2, and the single-crystal X-ray structure of the latter one was determined. Turnover frequencies of the catalysts during polymerization ranged from 36 to 241 cycles/mol/h. The obtained polymers exhibited weight-average molecular weights ranging from 24,000 to 438,500 g/mol, and the molar mass distribution varied between 1.8 and 4.3. Activity of the catalytic system and the molar mass of the polymer are influenced by the ligand structure of the complexes as well as other polymerization conditions such as monomer concentration and temperature. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1380–1389, 2003

Several alkyl side chains are bonded to each polymeric repeat unit using both coordinated ligands and electrostatically bound counterions to directly control the interface curvature of the self‐organized structures. 2,6‐Bis(octylaminomethyl)pyridine is Zn‐coordinated to poly(4‐vinylpyridine) (P4VP) with dodecylbenzenesulfonate (DBS) counterions, leading to multicomb polymeric supramolecules, poly[(4VP)Zn(2,6‐bis(octylaminomethyl)pyridine)(DBS)2]. Coordination is evidenced by infrared spectroscopy and visualized by quantum chemical calculations. The amorphous hexagonal self‐organized structures are characterized using X‐ray measurements.

The synthesis of a new series of iron(II)- and cobalt(II)-based complexes of the general formula M(N∩N∩N)Cl 2 (M=Fe; M=Co) bearing 2,6-bis(imin)pyridyl ligands [A–NC–Py–CN–A] that carry bulky, alkyl-free aromatic terminals (A=naphthyl, pyrenyl, 2-benzylphenyl, phenyl) or chiral cycloaliphatic auxiliary moieties (A=((−)- cis -myrtanyl) is described. The Fe(II) complexes are exceptionally active (up to 40800 kg PE/(mol M h) towards the polymerization of ethylene in the presence of methylaluminoxane (MAO) as activator. Varying the steric bulkiness of the aromatic groups in the tridentate ligands affects catalytic productivity, molecular weight and for the first time the microstructure of the resulted material. The Fe(II) precatalysts are an order of magnitude more active than the corresponding Co(II) precatalysts.

A synthesis of new chiral dihalo palladium(II)-(5, 7) and nickel(II) (6, 8) complexes bearing the ligands N,N′-bis{(−)-(cis)-myrtanyl}butylene-2,3-diimine (BMDI, 3) and the conformationally constrained bisoxazoline ligand ((1R,2S)-inda-box, 4) is described. Reaction of [(TMEDA)Pd(CH3)Cl] (TMEDA: N,N,N′,N′-tetramethylethylenediamine) with 4 followed by chloride abstraction with NaB(Arf)4 in the presence of CH3CN afforded the solvent stabilized, monoalkyl complex [(4)Pd(NCCH3)(CH3)]B(Arf)4 (9) (Arf: 3,5-bis(trifluoromethyl)benzene). The solid state structure of the dichloro palladium(II) complex [{(1R,2S)-inda-box}PdCl2] (7) was determined by X-ray structure analysis.

Palladium(II) complexes of the general type [Pd(L∩L)Cl2] (4–6) and their corresponding dicationic complexes [Pd(L∩L)(NCCH3)2](BF4)2 (7–9) (L∩L=[(1-(thiomethyl)-2-(diphenylarsino)ethane] (S∩As, 1) (4, 7) [1-(thiomethyl)-2-(diphenylphosphino)ethane] (S∩P, 2) (5, 8) and [1,2-bis(diphenylphosphino)ethane] (P∩P, 3) (6, 9) have been synthesized and utilized as catalysts for the polymerization reaction of bicyclo[2.2.1]hept-2-ene (norbornene). The dichloride complexes can be activated with methylaluminoxane (MAO), while the corresponding dicationic compounds were used as single component catalysts for the polymerization reactions. Catalytic performance of the new type of catalyst can be altered by modifying the donor atoms in the bidentate ligand. The activity of the Pd(II) complexes towards the polymerization reaction increases with increasing the trans-influence of the donor atoms (P∩P>S∩P>S∩As). The influence of donor atoms on the length of the PdCl bonds was elucidated by X-ray structure analysis carried out on the palladium(II) complex [Pd(S∩As)Cl2] (4).

Preparation of four dimeric nickel(II) complexes and three monomeric palladium(II) complexes bearing didentate pyridinylimine ligands is described. The solid-state structures of these compounds have been determined by single-crystal X-ray diffraction. After activation with methylaluminoxane (MAO) the nickel compounds were used as catalysts in ethylene polymerization producing nearly linear or primarily methyl-branched polymers. The effect of ligand environment was most evident on degree of branching, while catalytic activity and molecular weight of the polymer were more dependent on the general catalyst composition as well as reaction conditions. Activation of the dichloropalladium(II) complexes with MAO yields highly active catalysts for the polymerization of bicyclo[2.2.1]hept-2-ene (norbornene) whereas only low conversions (

The DNA-cleavage properties of the two copper(II) complexes, [Cu(mbpzbpy)Br(2)](H(2)O)(2.5) (1) and [Cu(mpzbpya)Cl](CH(3)OH) (2), obtained from the ligands 6,6'-bis(3,5-dimethyl-N-pyrazolmethyl)-2,2'-bipyridine) (mbpzbpy) and 6'-(3,5-dimethyl-N-pyrazolmethyl)-2,2'-bipyridine-6-carboxylic acid) (Hmpzbpya), respectively, are reported. Upon coordination to Cu(II) chloride in methanol, one arm of the ligand mbpzbpy is hydrolyzed to form mpzbpya. Under the same experimental conditions, the reaction of mbpzbpy with CuBr(2) does not lead to ligand hydrolysis. The ligand mpzbpya is coordinated to a copper(ii) ion generating a CuN(3)OCl chromophore, resulting in a distorted square-pyramidal environment, whereas with the N(4) mbpzbpy ligand, the Cu(II) ion is four-coordinated in a distorted square planar geometry. Both complexes promote the oxidative DNA cleavage of phiX174 phage DNA in the absence of reductant. The oxidative nature of the DNA cleavage reaction has been confirmed by religation and cell-transformation experiments. Studies using standard radical scavengers suggest the involvement of hydroxyl radicals in the oxidative cleavage of DNA. Although both compounds do convert form I (supercoiled) DNA to form II (nicked, relaxed form), only complex 1 is able to produce small amounts of form III (linearized DNA). This observation may be explained either by the attack of the copper(ii) complexes to only one single strand of DNA, or by a single cleavage event. Statistical analysis of relative DNA quantities present after the treatment with both copper(ii) complexes supports a random mode of DNA cleavage.