New chiral α‐diimine nickel(II) complexes bearing ortho‐sec‐phenethyl groups for ethylene polymerization

A series of new α‐diimine nickel(II) catalysts bearing bulky chiral sec‐phenethyl groups have been synthesized and characterized. The molecular structure of representative chiral ligand, bis[N,N′‐(4‐methyl‐2,6‐di‐sec‐phenethylphenyl)imino]‐1,2‐dimethylethane rac‐1c and chiral complexes, {bis[N,N′‐(4‐methyl‐2‐sec‐phenethylphenyl)imino]‐2,3‐butadiene}dibromidonickel rac‐2a and bis{bis[N,N′‐(4‐methyl‐2‐sec‐phenethylphenyl)imino]‐2,3‐butadiene}dibromidonickel rac‐2b, were confirmed by X‐ray crystallographic analysis. Complex rac‐2c bearing two chiral sec‐phenethyl groups in the ortho‐aryl position and a methyl group in the para‐aryl position, activated by diethylaluminum chloride (DEAC), showed highly catalytic activity for the polymerization of ethylene [4.12 × 10⁶ g PE (mol Ni.h.bar)^?1], and produced highly branched polyethylenes under low ethylene pressure (branching degree: 104, 118 and 126 branches/1000 C at 20, 40 and 60°C, respectively). Chiral 20‐electron bis‐α‐diimine Ni(II) complex rac‐2b also exhibited high activity toward ethylene polymerization [1.71 × 10⁶ g PE (mol Ni · h · bar)^?1]. The type and amount of branches of the polyethylenes obtained were determined by ¹H and ¹³C NMR. Copyright © 2013 John Wiley & Sons, Ltd.     

Vinyl polymerization of norbornene by nickel(II) complexes bearing β‐diketiminate ligands

Norbornene polymerizations were carried out using nickel(II) bromide complexes CH{C(R)NAr}₂NiBr ( 1 , R = CH₃, Ar = 2, 6 ? ⁱPr₂C₆H₃; 2 , R = CH₃, Ar = 2, 6‐Me₂C₆H₃; 3 , R = CF₃, Ar = 2, 6 ? ⁱPr₂C₆H₃; 4 , R = CF₃, Ar = 2, 6‐Me₂C₆H₃) in the presence of methylaluminoxane. Compound 3 is the most active norbornene polymerization catalyst of all the nickel complexes tested. The activity of theses catalysts increases with increases in steric bulk of the substituents on the aryl rings. The electronic nature of the ligand backbone also affects the activity. The resulting polynorbornenes are vinyl type by IR and NMR analyses. Copyright © 2007 John Wiley & Sons, Ltd.     

Half‐titanocene complexes bearing dianionic 6‐benzimidazolylpyridyl‐2‐carboximidate ligands: Synthesis,characterization, and their ethylene polymerization

6‐Benzimidazolylpyridyl‐2‐carboximidic half‐titanocene complexes, Cp′TiLCl (Cp′ = C₅H₅, MeC₅H₄, C₅Me₅, L = 6‐benzimidazolylpyridine‐2‐carboxylimidic, C1–C13 ), were synthesized and characterized along with single‐crystal X‐ray diffraction. The half‐titanocene chlorides containing substituted cyclopentadienyl groups, especially pentamethylcyclopentadienyl groups were more stable, while those without substituents on the cyclopentadienyl groups were easily transformed into their dimeric oxo‐bridged complexes, (CpTiL)₂O ( C14 and C15 ). In the presence of excessive amounts of methylaluminoxane (MAO) or modified methylaluminoxane (MMAO), all half‐titanocene complexes showed high catalytic activities for ethylene polymerization. The substituents on the Cp groups affected the catalytic behaviors of the complexes significantly, with less substituents favoring increased activities and higher molecular weights of the resultant polyethylenes. Effects of reaction conditions on catalytic behaviors were systematically investigated with catalytic systems of mononuclear C1 and dimeric C14 . With C1 /MAO, large MAO amount significantly increases the catalytic activity, while the temperature only has a slight effect on the productivity. In the case of C14 /MAO catalytic system, temperature above 60 °C and Al/Ti value higher than 5000 were necessary to observe good catalytic activities. In both systems, higher reaction temperature and low cocatalyst amount gave the polyethylenes with higher molecular weights. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3396–3410, 2008     

Novel nickel (II) complexes chelating β‐diketiminate ligands: synthesis and simultaneous polymerization and oligomerization of ethylene

Two novel nickel (II) complexes, CH{C(CF₃)NAr}₂NiBr ( 1 , Ar = 2,6‐ⁱPr₂C₆H₃ and 2 , 2,6‐Me₂C₆H₃), were synthesized by the reaction of the lithium salt of fluorinated β‐diketiminate backbone ligands with (1,2‐dimethoxyethane) nickel (II) bromide [(DME)NiBr₂]. The solid‐state structure of nickel (II) complex 2 as a dimer reveals four‐coordination and a tetrahedral geometry with bromide bridged by single crystal X‐ray measurement. Both complexes catalyze simultaneous polymerization and oligomerization of ethylene when activated by methylaluminoxane (MAO). It was found that the reaction temperature has a pronounced effect on the activity of ethylene polymerization and the molecular weight of obtained polyethylene. In addition, the nickel catalytic systems predominantly produce linear polyethylene with unsaturated end groups. Copyright © 2006 John Wiley & Sons, Ltd.     

Synthesis of long‐chain‐branched polyethylene by ethylene homopolymerization with a novel nickel(II) α‐diimine catalyst

Long‐chain‐branched polyethylene with a broad or bimodal molecular weight distribution was synthesized by ethylene homopolymerization via a novel nickel(II) α‐diimine complex of 2,3‐bis(2‐phenylphenyl)butane diimine nickel dibromide ({[2‐C₆H₄(C₆H₅)]? N?C? (CH₃)C(CH₃)?N? [2‐C₆H₄(C₆H₅)]}NiBr₂) that possessed two stereoisomers in the presence of modified methylaluminoxane. The influences of the polymerization conditions, including the temperature and Al/Ni molar ratio, on the catalytic activity, molecular weight and molecular weight distribution, degree of branching, and branch length of polyethylene, were investigated. The resultant products were confirmed by gel permeation chromatography, gas chromatography/mass spectrometry, and ¹³C NMR characterization to be composed of higher molecular weight polyethylene with only isolated long‐branched chains (longer than six carbons) or with methyl pendant groups and oligomers of linear α‐olefins. The long‐chain‐branched polyethylene was formed mainly through the copolymerization of ethylene growing chains and macromonomers of α‐olefins. The presence of methyl pendant groups in the polyethylene main chain implied a 2,1‐insertion of the macromonomers into [Ni]? H active species. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1325–1330, 2005     

Synthesis of ferrocene‐containing N‐aryloxo β‐ketoiminate lanthanide complexes and polymerization of ε‐caprolactone

The synthesis, characterization and ε‐caprolactone polymerization behavior of lanthanide amido complexes stabilized by ferrocene‐containing N‐aryloxo functionalized β‐ketoiminate ligand FcCOCH₂C(Me)N(2‐HO‐5‐Bu^t‐C₆H₃) (LH₂, Fc = ferrocenyl) are described. The lanthanide amido complexes [LLnN(SiMe₃)₂(THF)]₂ [Ln = Nd ( 1 ), Sm ( 2 ), Yb ( 3 ), Y ( 4 )] were synthesized in good yields by the amine elimination reactions of LH₂ with Ln[N(SiMe₃)₂]₃(µ‐Cl)Li(THF)₃ in a 1:1 molar ratio in THF. These complexes were characterized by IR spectroscopy and elemental analysis, and ¹H NMR spectroscopy was added for the analysis of complex 4 . The definitive molecular structures of complexes 1 and 3 were determined by X‐ray diffraction studies. Complexes 1 – 4 can initiate the ring‐opening polymerization of ε‐caprolactone with moderate activity. Copyright © 2011 John Wiley & Sons, Ltd.     

Synthesis and characterization of a series of 2‐aminopyridine nickel(II) complexes and their catalytic properties toward ethylene polymerization

A series of 2‐aminopyridine Ni(II) complexes bearing different substituent groups {(2‐PyCH₂NAr)NiBr, Ar = 2,4,6‐trimethylphenyl ( 3a) , 2,6‐dichlorophenyl ( 3b ), 2,6‐dimethylphenyl ( 3c) , 2,6‐diisopropylphenyl ( 3d ), 2,6‐difluorophenyl ( 3e ); (2‐PyCH₂NHAr)₂NiBr₂, Ar = 2,6‐diisopropylphenyl ( 4a )} have been synthesized and investigated as precatalysts for ethylene polymerization in the presence of methylaluminoxane (MAO). High molecular weight branched polymers as well as short‐chain oligomers were simultaneously produced with these complexes. Enhancing the steric bulk of the ortho‐aryl‐substituents of the catalyst resulted in higher ratio of solid polymer to oligomer and higher molecular weight of the polymer. With ortho‐haloid‐substitution, the catalysts afforded a product with low polymer/oligomer ratio ( 3b ) and even only oligomers ( 3e ) in which C₁₄H₂₈ had the maximum content. Compared with complex 3d containing ionic ligand, complex 4a containing neutral ligand exhibited obviously low catalytic activity for ethylene polymerization. The molecular weight, molecular weight distribution, and microstructure of the resulted polymer were characterized by gel permeation chromatography and ¹³C NMR spectrogram. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1618–1628, 2008     

Salicylaldiminato nickel(II) catalysts with 5‐halo‐3‐methoxy groups for ethylene polymerization

Two neutral salicylaldiminato methyl pyridine nickel(II) complexes were synthesized and evaluated for ethylene polymerization. Each catalyst bears a methoxy group in the 3‐position and a halogen atom in the 5‐position of the salicyl ligand, chlorine in case of catalyst 3a and bromine in 3b . Molecular structures of the catalysts were obtained by X‐ray crystallography. The resulting polymerization activities, for example, indicated by a maximum turnover frequency of 4,870 mol ethylene/(mol Ni × h) for 1‐h runs obtained with 3a , were higher than those of similar catalysts at comparable conditions reported in the literature. Catalyst 3a was slightly more active than catalyst 3b . The polymers are branched as measured by ¹H NMR and ¹³C NMR. This was also reflected in the melting temperatures between 76 and 113 °C obtained by differential scanning calorimetry. By using gel permeation chromatography measurements, it was determined that the M_w of the polymers ranges between about 5,400 and 21,600 g/mol. In particular, the effect of the polymerization temperature on the catalyst activity, degree of branching, and molecular weight properties has been described. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Radical‐initiated polymerization of β‐methyl‐α‐methylene‐γ‐butyrolactone

β‐Methyl‐α‐methylene‐γ‐butyrolactone (MMBL) was synthesized and then was polymerized in an N,N‐dimethylformamide (DMF) solution with 2,2‐azobisisobutyronitrile (AIBN) initiation. The homopolymer of MMBL was soluble in DMF and acetonitrile. MMBL was homopolymerized without competing depolymerization from 50 to 70 °C. The rate of polymerization (R_p) for MMBL followed the kinetic expression R_p = [AIBN]^0.54[MMBL]^1.04. The overall activation energy was calculated to be 86.9 kJ/mol, k_p/k_t^1/2 was equal to 0.050 (where k_p is the rate constant for propagation and k_t is the rate constant for termination), and the rate of initiation was 2.17 × 10^?8 mol L^?1 s^?1. The free energy of activation, the activation enthalpy, and the activation entropy were 106.0, 84.1, and 0.0658 kJ mol^?1, respectively, for homopolymerization. The initiation efficiency was approximately 1. Styrene and MMBL were copolymerized in DMF solutions at 60 °C with AIBN as the initiator. The reactivity ratios (r₁ = 0.22 and r₂ = 0.73) for this copolymerization were calculated with the Kelen–Tudos method. The general reactivity parameter Q and the polarity parameter e for MMBL were calculated to be 1.54 and 0.55, respectively. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1759–1777, 2003     

Efficient catalysts for ring‐opening polymerization of ε‐caprolactone and β‐butyrolactone: Synthesis and characterization of zinc complexes based on benzotriazole phenoxide ligands

A series of efficient zinc catalysts supported by sterically bulky benzotriazole phenoxide ( BTP ) ligands are synthesized and structurally characterized. The reactions of diethyl zinc (ZnEt₂) with ^CMe2PhBTP ‐H, ^t‐BuBTP ‐H, and ^TMClBTP ‐H yield monoadduct [(μ‐ BTP )ZnEt]₂ ( 1 – 3 ), respectively. Bisadduct complex [( ^t‐BuBTP )₂Zn] ( 4 ) results from treatment of ZnEt₂ with ^t‐BuBTP ‐H (2 equiv.) in toluene, but treatment of ^TMClBTP ‐H with ZnEt₂ in the same stoichiometric proportion in Et₂O produces five‐coordinated monomeric complex [( ^TMClBTP )₂Zn(Et₂O)] ( 5 ). The molecular structures of compounds 1 , 4 , and 5 are characterized by X‐ray crystal structure determinations. All complexes 1 – 5 are efficient catalysts for the ring‐opening polymerization of ε‐caprolactone (ε‐CL) in the presence of 9‐anthracenemethanol. Experimental results indicate that complex 3 exhibits the greatest activity with well‐controlled character among these complexes. The polymerizations of ε‐CL and β‐butyrolactone catalyzed by 3 are demonstrated in a “living” character with narrow polydispersity indices (monomer‐to‐initiator ratio in the range of 25–200, PDIs ≤ 1.10). The “immortal” character of 3 provides a way to synthesize as much as 16‐fold polymer chains of poly(ε‐CL) (PCL) with narrow PDI in the presence of a catalyst in a small proportion. The controlled fashion of complex 3 also enabled preparation of the PCL‐b‐poly(3‐hydroxybutyrate) copolymer. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Separation of α‐ from β‐arylalanines by nickel nitrilotriacetate chromatography

A method is described to separate α‐ from β‐arylalanines by ligand exchange chromatography on a nickel nitrilotriacetate agarose column with UV monitoring of the effluent. Separate mixtures containing an α‐ and β‐arylalanine pair (1 mg of each) were individually loaded onto the nickel resin pre‐equilibrated with the mobile phase at room temperature, and the amino acids were eluted from the column with a gradient from pH 12.0–8.0. The β‐arylalanines eluted first, followed by the α‐isomers. The four α/β‐amino acid pairs tested were well separated with baseline resolution. An aliquot of each fraction was chemically treated to derivatize the amino acids to their N‐acyl methyl ester analogs, and their identities were confirmed by GC/MS analysis. The sample recovery was quantitative (>98%), and the column matrix was very resilient, as demonstrated by consistent separation of the solutes after ～100 preparative cycles.     

Syntheses,and Crystal Structures of Indium Complexes with η2‐Piperidinyldithiocarbamate and η2‐Pyridine‐2‐Thionate Containing Ligands: Structures of [In(η2‐S2CNC5H10)3] and [In(η2‐pyS)3]

The η²‐thio‐indium complexes [In(η²‐thio)₃] (thio = S₂CNC₅H₁₀, 2 ; SNC₄H₄, (pyridine‐2‐thionate, pyS, 3 ) and [In(η²‐pyS)₂(η²‐acac)], 4 , (acac: acetylacetonate) are prepared by reacting the tris(η²‐acac)indium complex [In(η²‐acac)₃], 1 with HS₂CNC₅H₁₀, pySH, and pySH with ratios of 1:3, 1:3, and 1:2 in dichloromethane at room temperature, respectively. All of these complexes are identified by spectroscopic methods and complexes 2 and 3 are determined by single‐crystal X‐ray diffraction. Crystal data for 2 : space group, C2/c with a = 13.5489(8) Å, b = 12.1821(7) Å, c = 16.0893(10) Å, β = 101.654(1)°, V = 2600.9(3) ų, and Z = 4. The structure was refined to R = 0.033 and Rw = 0.086; Crystal data for 3 : space group, P2₁ with a = 8.8064 (6) Å, b = 11.7047 (8) Å, c = 9.4046 (7) Å, β = 114.78 (1)°, V = 880.13(11) ų, and Z = 2. The structure was refined to R = 0.030 and Rw = 0.061. The geometry around the metal atom of the two complexes is a trigonal prismatic coordination. The piperidinyldithiocarbamate and pyridine‐2‐thionate ligands, respectively, coordinate to the indium metal center through the two sulfur atoms and one sulfur and one nitrogen atoms, respectively. The short C‐N bond length in the range of 1.322(4)–1.381(6) Å in 2 and C‐S bond length in the range of 1.715(2)–1.753(6) Å in 2 and 3 , respectively, indicate considerable partial double bond character.     

Synthesis,characterization, and degradation of poly(ethylene‐b‐ε‐caprolactone) diblock copolymer

Poly(ethylene‐b‐ε‐caprolactone) (PE‐b‐PCL) diblock copolymers were synthesized by ring‐opening polymerization (ROP) of ε‐caprolactone (CL) with α‐hydroxyl‐ω‐methyl polyethylene (PE‐OH) as a macroinitiator and ammonium decamolybdate (NH₄)₈[Mo₁₀O₃₄] as a catalyst. Polymerization was conducted in bulk (130–150°C) with high yield (87–97%). Block copolymers with different compositions were obtained and characterized by ¹H and ¹³C NMR, MALDI‐TOF, SAXS, and DSC. End‐group analysis by NMR and MALDI‐TOF indicates the formation of α‐hydroxyl‐ω‐methyl PE‐b‐PCL. The PE‐b‐PCL degradation was studied using thermogravimetric analysis (TGA) and alkaline hydrolysis. The PCL block was hydrolyzed by NaOH (4M), without any effect on the PE segment. Copyright © 2009 John Wiley & Sons, Ltd.     

Tetrylenes chelated by bifunctional β‐diketiminate ligand: structure and possible applications

The synthesis and structure of heteroleptic tetrylenes containing bifunctional β‐diketiminate ligand are reported. Compounds were prepared via a protolytic reaction of free β‐diketimine {N‐[(2‐MeO)C₆H₅]}N═C(Me)CH═C(Me)N(H){N′‐[(2‐MeO)C₆H₅]} (L^COH) and {N‐[(2‐MeO)C₆H₅]}N?CHCH?CHN(H){N′‐[(2‐MeO)C₆H₅]} (L^HOH), respectively, with corresponding bis(amide) – M[N(SiMe₃)₂]₂ (M = Ge, Sn, Pb) – in equimolar ratio or via the salt elimination route from lithium precursors generated from L^HOH/L^COH species and slight excess of SnCl₂ or GeCl₂.dioxane complex. Only heteroleptic complexes were obtained by the mentioned methods. Products were characterized by multinuclear NMR spectroscopy techniques and structures of four of them have been determined by X‐ray diffraction methods. Complexes L^HOGeCl and L^COSnN(SiMe₃)₂ crystallize as monomers with the three‐coordinated metal centres by one chloro or amido ligand and one bidentate β‐diketiminato unit, in contrast to the structure of L^COSnCl, which reveals a dimeric character and compound L^COPbN(SiMe₃)₂, where the central atom of lead is five‐coordinated by methoxy groups of the ligand. Complex L^COSnN(SiMe₃)₂ was tested as a catalyst for polymerization of various epoxides_. Copyright © 2014 John Wiley & Sons, Ltd.     

Synthesis and characterization of amphiphilic copolymer of linear poly(ethylene oxide) linked with [poly(styrene‐co‐2‐hydroxyethyl methacrylate)‐graft‐poly(ε‐caprolactone)] using sequential controlled polymerization

A well‐defined amphiphilic copolymer of ‐poly(ethylene oxide) (PEO) linked with comb‐shaped [poly(styrene‐co‐2‐hydeoxyethyl methacrylate)‐graft‐poly(ε‐caprolactone)] (PEO‐b‐P(St‐co‐HEMA)‐g‐PCL) was successfully synthesized by combination of reversible addition‐fragmentation chain transfer polymerization (RAFT) with ring‐opening anionic polymerization and coordination–insertion ring‐opening polymerization (ROP). The α‐methoxy poly(ethylene oxide) (mPEO) with ω,3‐benzylsulfanylthiocarbonylsufanylpropionic acid (BSPA) end group (mPEO‐BSPA) was prepared by the reaction of mPEO with 3‐benzylsulfanylthiocarbonylsufanyl propionic acid chloride (BSPAC), and the reaction efficiency was close to 100%; then the mPEO‐BSPA was used as a macro‐RAFT agent for the copolymerization of styrene (St) and 2‐hydroxyethyl methacrylate (HEMA) using 2,2‐azobisisobutyronitrile as initiator. The molecular weight of copolymer PEO‐b‐P(St‐co‐HEMA) increased with the monomer conversion, but the molecular weight distribution was a little wide. The influence of molecular weight of macro‐RAFT agent on the polymerization procedure was discussed. The ROP of ε‐caprolactone was then completed by initiation of hydroxyl groups of the PEO‐b‐P(St‐co‐HEMA) precursors in the presence of stannous octoate (Sn(Oct)₂). Thus, the amphiphilic copolymer of linear PEO linked with comb‐like P(St‐co‐HEMA)‐g‐PCL was obtained. The final and intermediate products were characterized in detail by NMR, GPC, and UV. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 467–476, 2006     

Synthesis and Characterization of β‐Cyclodextrin Based Functional Monomers and its Copolymers with N‐isopropylacrylamide

Two novel monovinyl β‐cyclodextrin (β‐CD) monomers are synthesized. Their chemical compositions are characterized by means of element analysis, NMR and FT‐IR spectroscopy. The results show that the synthesis techniques used are convenient and efficient. Using N‐isopropylacrylamide as a comonomer, two novel linear copolymers can also be synthesized.

Synthesis route of monovinyl β‐CD monomers.     

Synthesis of new optically active α,α′,β‐trisubstituted‐β‐lactones as monomers for stereoregular biopolyesters

Various optically active (4R)‐alkyloxycarbonyl‐3,3‐dialkyl‐2‐oxetanones as monomers were synthesized from L‐(S)‐malic acid in six steps to prepare a new family of stereopolyesters for biomedical applications. The synthesis began with an esterification followed of a dialkylation in the aim to introduce hydrophobic groups as methyl or reactive group as allyl. Then, a saponification has permitted to obtain the corresponding diacids that reacted with appropriate alcohols to furnish different monoesters. The last and most important step was activation of hydroxyl group of monoesters with the asymmetric carbon configuration inversion according to the Mitsunobu reaction. Thus, this reaction has provided lactones from monoesters with 100% enantiomeric excess which was confirmed by ¹H NMR and by the synthesis of corresponding isotactic and semicrystalline homopolyesters. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2586–2597     

Polymerization of β‐pinene with Schiff‐base nickel complexes catalyst: Synthesis of relatively high molecular weight poly(β‐pinene) at high temperature with high productivity

A series of easily accessible and stable Schiff‐base nickel complexes (complex 1 – 4 ) in conjunction with methylaluminoxane (MAO) were employed for the synthesis of relatively high molecular weight β‐pinene polymers at high temperature with high productivity. The ligand structure of the complex had a substantial effect on the polymerization in terms of the productivity and the molecular weight. With complex 4 in the presence of MAO, high molecular weight polymers of β‐pinene (M_n ～ 10,900) were obtained at 40 °C with an extremely high productivity up to 1.25 × 10⁷ g polyβ‐pinene/mol of Ni. ¹H NMR analyses showed that the obtained β‐pinene polymer was structurally identical to that formed by conventional cationic Lewis acid initiators. The polymerization was presumably initiated by the nickel cation formed by the reaction of the schiff‐base nickel complex and MAO, while the propagation proceeded in a manner typical for a conventional carbocationic polymerization process. Direct evidence for the carbocationic polymerization was offered by the fact that quenching of the polymerization with methanol at a low monomer conversion resulted in incorporation of a methoxyl end group into the polymer chain. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3739–3746, 2007