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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.

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.

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 (