Polymerization of methyl methacrylate in the presence of iron(II) complex with tetradentate nitrogen ligands under conditions of atom transfer radical polymerization

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.     

Aurophilicity-coordination interplay in the design of cyano-bridged nickel(II)-Gold(I) bimetallic assemblies: structural and computational studies of the gold(I)-gold(I) interactions

Two polymorphic cyano-bridged Au(I)-Ni(II) bimetallic complexes of formulas [Ni(en)2Au(CN)2][Au(CN)2] (1) and [Ni(en)2[Au(CN)2]2] (2) have been prepared from the 1:2 reaction between [Au(CN)2]- and either [Ni(en)2Cl2]Cl or [Ni(en)3]Cl2.2H2O, respectively. The structure of 1 consists of polymeric cationic chains of alternating [Au(CN)2]- and [Ni(en)2]2+ units running along the a axis and [Au(CN)2]- anions lying between the chains. The noncoordinated dicyanoaurate anions are aligned perpendicular to the ac plane and involved in aurophilic interactions with the bridging dicyanoaurate groups, ultimately leading to a 2D bimetallic grid. The structure of 2 consists of trinuclear molecules made of two [Au(CN)2]- anions linked to [Ni(en)2]2+ unit in trans configuration. Trinuclear units are joined by aurophilic interactions to form 1D zigzag chains. The magnetic properties of these compounds are strongly dominated by the local anisotropy of the octahedral Ni(II) ions, thus indicating that the magnetic exchange interaction mediated by dicyanoaurate bridging groups, if it exists, is very weak. To get insight into the electronic properties of the inter- and intramolecular interactions of the [Au(CN)2]- building blocks, the structures of different aggregates of dicyanogold units were optimized and then analyzed by making use of atoms-in-molecules (AIM) theory. Moreover, bond indices were calculated by methods based upon nonlinear population analysis.     

Iron(II)‐ and Cobalt(II) Complexes with Tridentate Bis(imino)pyridine Nitrogen Ligands Bearing Chiral Bulky Aliphatic and Aromatic Substituents: Crystal Structure of [CoCl2{2, 6‐bis[R‐(+)‐(bornylimino)methyl]pyridine}]

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) Å, b = 28.3153(14) Å, c = 13.537(2) Å, V = 2908.1(6) ų, Z = 4. The coordination sphere around Co is distorted trigonal bipyramidal.     

Ligand creation via linking—a rapid and convenient method for construction of novel supported PyOX-ligands

A novel supported amino alcohol linker was synthesized and utilized for attachment of picolinic acid derivatives onto different supports. When the resin bound molecule was further activated, the PyOX-moiety could be constructed reliably in enantiopure form. Furthermore, an efficient Pd-catalyzed modification of a picolinic acid derivative is presented.     

Polymerization of ethene with zirconocene catalysts: an experimental and quantum chemical study of the influence of para-substituent in benzyl in bis{η-(1-benzyl)indenyl}zirconium dichlorides

The meso- and rac-like isomers of bis{η⁵-(1-benzyl)indenyl}zirconium dichloride (5), bis{η⁵-(1-para-methoxybenzyl)indenyl}zirconium dichloride (6), bis{η⁵-(1-para-fluoro-benzyl)indenyl}zirconium dichloride (7) and bis{η⁵-(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.     

Rapid Autoxidation Forms Highly Oxidized RO2 Radicals in the Atmosphere

Gas‐phase oxidation routes of biogenic emissions, mainly isoprene and monoterpenes, in the atmosphere are still the subject of intensive research with special attention being paid to the formation of aerosol constituents. This laboratory study shows that the most abundant monoterpenes (limonene and α‐pinene) form highly oxidized RO₂ radicals with up to 12 O atoms, along with related closed‐shell products, within a few seconds after the initial attack of ozone or OH radicals. The overall process, an intramolecular ROO→QOOH reaction and subsequent O₂ addition generating a next R′OO radical, is similar to the well‐known autoxidation processes in the liquid phase (QOOH stands for a hydroperoxyalkyl radical). Field measurements show the relevance of this process to atmospheric chemistry. Thus, the well‐known reaction principle of autoxidation is also applicable to the atmospheric gas‐phase oxidation of hydrocarbons leading to extremely low‐volatility products which contribute to organic aerosol mass and hence influence the aerosol–cloud–climate system.     

One-pot synthesis of 3,4-disubstituted 1H-pyrroles from 2-tropanones

3,4-Disubstituted pyrroles (2, 3) were prepared from 6/7-carboxyethyl-3-phenyl-3-tropen-2-ones (1) regioselectively and with high yields by using tosylmethyl isocyanide (TosMIC). This procedure enables the synthesis of pyrroles substituted with two distinct groups: a phenyl group and a substituted pyrrolidine analogue. The crystal structure of product 2a was determined, and the analogous derivatives were identified by (1)H and (13)C NMR spectroscopy.     

Parallel screening of homogeneous copper catalysts for the oxidation of benzylic alcohols with molecular oxygen in aqueous solutions

A simple and efficient parallel screening method to evaluate the catalytic activities of homogeneous copper complexes for the oxidation of benzylic alcohols in aqueous solutions with molecular oxygen is reported. Copper(II) sulfate was treated in situ with 22 nitrogen donor ligands, and the catalytic activities of these combinations were studied at four different pH values with two substrates (benzyl alcohol and 3,4-dimethoxy benzyl alcohol (veratryl alcohol)), resulting in 176 oxidation experiments in the primary screening stage. Copper complexes based on N,N,N',N'-tetramethyl ethylenediamine (TMEDA), 9,10-diaminephenanthrene (DAPHEN), and 1,2-diaminocyclohexane (DACH) were determined to be the most active catalysts. In the second screenings, the influence of reaction conditions on Cu(DACH)-, Cu(TMEDA)-, and Cu(DAPHEN)-catalyzed reactions were investigated in more detail. It was found that highly basic reaction conditions favor the reaction with the exception of Cu(TMEDA), which is active at a lower pH range. Under optimized conditions, Cu(DAPHEN) catalyzes the transformation of veratryl alcohol to the corresponding aldehyde with 100% conversion.     

High molar mass ethene/1‐olefin copolymers synthesized with acenaphthyl substituted metallocene catalysts

The influence of ligand structure on copolymerization properties of metallocene catalysts was elucidated with three C₁‐symmetric methylalumoxane (MAO) activated zirconocene dichlorides, ethylene(1‐(7, 9)‐diphenylcyclopenta‐[a]‐acenaphthadienyl‐2‐phenyl‐2‐cyclopentadienyl)ZrCl₂ ( 1 ), ethylene(1‐(7, 9)‐diphenylcyclopenta‐[a]‐acenaphthadienyl‐2‐phenyl‐2‐fluorenyl)ZrCl₂ ( 2 ), and ethylene(1‐(9)‐fluorenyl‐(R)1‐phenyl‐2‐(1‐indenyl)ZrCl2 ( 3 ). Polyethenes produced with 1 /MAO had considerable, ca. 10% amount of trans‐vinylene end groups, resulting from the chain end isomerization prior to the chain termination. When ethene was copolymerized with 1‐hexene or 1‐hexadecene using 1 /MAO, molar mass of the copolymers varied from high to moderate (531–116 kg/mol) depending on the comonomer feed. At 50% comonomer feed, ethene/1‐olefin copolymers with high hexene or hexadecene content (around 10%) were achievable. In the series of catalysts, polyethenes with highest molar mass, up to 985 kg/mol, were obtained with sterically most crowded 2 /MAO, but the catalyst was only moderately active to copolymerize higher olefins. Catalyst 3 /MAO produced polyethenes with extremely small amounts of trans‐vinylene end groups and relatively low molar mass 1‐hexene copolymers (from 157 to 38 kg/mol) with similar comonomer content as 1 . These results indicate that the catalyst structure, which favors chain end isomerization, is also capable to produce high molar mass 1‐olefin copolymers with high comonomer content. In addition, an exceptionally strong synergetic effect of the comonomer on the polymerization activity was observed with catalyst 3 /MAO. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 373–382, 2008