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1.
Dr. Heng Liao Dr. Liu Zhong Dr. Zefan Xiao Dr. Ting Zheng Prof. Haiyang Gao Prof. Qing Wu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(39):14048-14055
A series of novel α‐diamine nickel complexes, (ArNH‐C(Me)‐(Me)C‐NHAr)NiBr2, 1 : Ar=2,6‐diisopropylphenyl, 2 : Ar=2,6‐dimethylphenyl, 3 : Ar=phenyl), have been synthesized and characterized. X‐ray crystallographic analysis showed that the coordination geometry of the α‐diamine nickel complexes is markedly different from conventional α‐diimine nickel complexes, and that the chelate ring (N‐C‐C‐N‐Ni) of the α‐diamine nickel complex is significantly distorted. The α‐diamine nickel catalysts also display different steric effects on ethylene polymerization in comparison to the α‐diimine nickel catalyst. Increasing the steric hindrance of the α‐diamine ligand by substitution of the o‐methyl groups with o‐isopropyl groups leads to decreased polymerization activity and molecular weight; however, catalyst thermal stability is significantly enhanced. Living polymerizations of ethylene can be successfully achieved using 1 /Et2AlCl at 35 °C or 2 /Et2AlCl at 0 °C. The bulky α‐diamine nickel catalyst 1 with isopropyl substituents can additionally be used to control the branching topology of the obtained polyethylene at the same level of branching density by tuning the reaction temperature and ethylene pressure. 相似文献
2.
Hao Zou Fang Ming Zhu Qing Wu Jiao Yan Ai Shang An Lin 《Journal of polymer science. Part A, Polymer chemistry》2005,43(7):1325-1330
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 相似文献
3.
Linear and nonlinear optical properties of two new nickel(diimine)(dithiolate) complexes, nickel(4,4′‐dinitro2,2′‐bipyridyl)(tfd), Ni(NO2bipy)(tfd) , (tfd = 1,2‐trifluoromethylethene‐1,2‐dithiolate) and nickel(4,7‐diphenyl‐1,10‐phenathroline)(tfd), Ni(dpphen)(tfd) are reported. Ni(NO2bipy)(tfd) has a potent electronic acceptor substituted on the diimine ligand and exhibits an enhanced molecular first hyperpolarizability (β0 = ?31 × 10?30 esu), which is more than three times greater than that (β0 = ?10 × 10?30 esu) of Ni(dpphen)(tfd). Ni(NO2bipy)(tfd) also possesses the longest absorption wavelength, the largest solvatochromic shift, and one of the largest dipole moment changes (‐16 debye from ground to excited state) among nickel(diimine)(dithiolate) complexes. Crystal X‐ray structure of Ni(NO2bipy)(tfd) is used to compared the π‐bonding structure of central (N=C‐C=N)Ni(S‐C=C‐S) unit with that of previously known nickel(4,4′‐bis(butyloxycarbonyl)‐2,2′‐bipyridyl)(tfd), Ni(CO2Bubipy)(tfd). 相似文献
4.
α‐keto‐β‐diimine nickel‐catalyzed olefin polymerization: Effect of ortho‐aryl substituents and preparation of stereoblock copolymers 下载免费PDF全文
Anatolij Sokolohorskyj Ondřej Železník Ivana Císařová Johannes Lenz Albena Lederer Jan Merna 《Journal of polymer science. Part A, Polymer chemistry》2017,55(15):2440-2449
A series of α‐keto‐β‐diimine nickel complexes (Ar‐N = C(CH3)‐C(O)‐C(CH3)=N‐Ar)NiBr2; Ar = 2,6‐R‐C6H3‐, R = Me, Et, iPr, and Ar = 2,4,6‐Me3‐C6H3‐) was prepared. All corresponding ligands are unstable even under an inert atmosphere and in a freezer. Stable copper complex intermediates of ligand synthesis and ethyl substituted nickel complex were isolated and characterized by X‐ray. All nickel complexes were used for the polymerization of ethene, propylene, and hex‐1‐ene to investigate their livingness and the extent of chain‐walking. Low‐temperature propene polymerization with less bulky ortho‐substituents was less isospecific than the one with isopropyl derivative. Propene stereoblock copolymers were prepared by iPr derivative combining the polymerization at low temperature to prepare isotactic polypropylene (PP) block and at a higher temperature, supporting chain‐walking, to obtain amorphous regioirregular PP block. Alternatively, a copolymerization of propene with ethene was used for the preparation of amorphous block. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2440–2449 相似文献
5.
Synthesis of highly branched polyethylene using para‐phenyl‐substituted α‐diimine nickel catalysts 下载免费PDF全文
A series of para‐phenyl‐substituted α‐diimine nickel complexes, [(2,6‐R2‐4‐PhC6H2N═C(Me))2]NiBr2 (R = iPr ( 1 ); R = Et ( 2 ); R = Me ( 3 ); R = H ( 4 )), were synthesized and characterized. These complexes with systematically varied ligand sterics were used as precatalysts for ethylene polymerization in combination with methylaluminoxane. The results indicated the possibility of catalytic activity, molecular weight and polymer microstructure control through catalyst structures and polymerization temperature. Interestingly, it is possible to tune the catalytic activities ((0.30–2.56) × 106 g (mol Ni·h)?1), polymer molecular weights (Mn = (2.1–28.6) × 104 g mol?1) and branching densities (71–143/1000 C) over a very wide range. The polyethylene branching densities decreased with increasing bulkiness of ligand and decreasing polymerization temperature. Specifically, methyl‐substituted complex 3 showed high activities and produced highly branched amorphous polyethylene (up to 143 branches per 1000 C). 相似文献
6.
Semi‐Crystalline Polar Polyethylene: Ester‐Functionalized Linear Polyolefins Enabled by a Functional‐Group‐Tolerant,Cationic Nickel Catalyst 下载免费PDF全文
Dr. Brian K. Long Dr. James M. Eagan Dr. Michael Mulzer Prof. Geoffrey W. Coates 《Angewandte Chemie (International ed. in English)》2016,55(25):7106-7110
A dibenzobarrelene‐bridged, α‐diimine NiII catalyst (rac‐ 3 ) was synthesized and shown to have exceptional behavior for the polymerization of ethylene. The catalyst afforded high molecular weight polyethylenes with narrow dispersities and degrees of branching much lower than those made by related α‐diimine nickel catalysts. Catalyst rac‐ 3 demonstrated living behavior at room temperature, produced linear polyethylene (Tm=135 °C) at ?20 °C, and, most importantly, was able to copolymerize ethylene with the biorenewable polar monomer methyl 10‐undecenoate to yield highly linear ester‐functionalized polyethylene. 相似文献
7.
In this Communication, the copolymerization of ethylene with a sterically hindered α‐olefin comonomer, γ‐trisubstituted 3,3‐dimethyl‐1‐butene (DMB), using a chain‐walking Pd‐diimine catalyst, [(ArNC(Me) (Me)CNAr)Pd(CH3)(NCMe)]SbF6 (Ar2,6‐(iPr)2C6H3) ( 1 ) is reported. In spite of its high steric bulkiness in the close proximity of the double bond, appreciable DMB incorporations (up to 3 mol‐%) are successfully achieved in the copolymers. The chain microstructure of the copolymers is elucidated, and the effect of DMB incorporation on polymer topology and thermal properties are examined. This work thus demonstrates the high capability of the Pd‐diimine catalyst in incorporating sterically encumbered α‐olefins.
8.
Chun‐Lei Song Li‐Ming Tang Yan‐Guo Li Xiao‐Fang li Jie Chen Yue‐Sheng Li 《Journal of polymer science. Part A, Polymer chemistry》2006,44(6):1964-1974
A series of α‐diimine nickel(II) complexes containing chloro‐substituted ligands, [(Ar)N?C(C10H6)C?N(Ar)]NiBr2 ( 4a , Ar = 2,3‐C6H3Cl2; 4b , Ar = 2,4‐C6H3Cl2; 4c , Ar = 2,5‐C6H3Cl2; 4d , Ar = 2,6‐C6H3Cl2; 4e , Ar = 2,4,6‐C6H2Cl3) and [(Ar)N?C(C10H6)C?N(Ar)]2NiBr2 ( 5a , Ar = 2,3‐C6H3Cl2; 5b , Ar = 2,4‐C6H3Cl2; 5c , Ar = 2,5‐C6H3Cl2), have been synthesized and investigated as precatalysts for ethylene polymerization. In the presence of modified methylaluminoxane (MMAO) as a cocatalyst, these complexes are highly effective catalysts for the oligomerization or polymerization of ethylene under mild conditions. The catalyst activity and the properties of the products were strongly affected by the aryl‐substituents of the ligands used. Depending on the catalyst structure, it is possible to obtain the products ranging from linear α‐olefins to high‐molecular weight polyethylenes. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1964–1974, 2006 相似文献
9.
Alex S. Ionkin William J. Marshall Douglas J. Adelman Aaron L. Shoe Rupert E. Spence Tuyu Xie 《Journal of polymer science. Part A, Polymer chemistry》2006,44(8):2615-2635
A new series of nitro‐substituted bis(imino)pyridine ligands {2,6‐bis[1‐(2‐methyl‐4‐nitrophenylimino)ethyl]pyridine, 2,6‐bis[1‐(4‐nitrophenylimino)ethyl]pyridine, (1‐{6‐[1‐(4‐nitro‐phenylimino)‐ethyl]‐pyridin‐2‐yl}‐ethylidene)‐(2,4,6‐trimethyl‐phenyl)‐amine, and 2,6‐bis[1‐(2‐methyl‐3‐nitrophenylimino)ethyl]pyridine} and their corresponding Fe(II) complexes [{p‐NO2? o‐Me? Ph? N?C(Me)? Py? C(Me)?N? Ph? o‐ Me? p‐NO2}FeCl2 ( 10 ), L2FeCl2 ( 11 ), {m‐NO2? o‐Me? Ph? N?C(Me)? Py? C(Me)?N? Ph? o‐Me? m‐NO2}FeCl2 ( 12 ), and {p‐NO2? Ph? N?C(Me)? Py? C(Me)?N? Mes}FeCl2 ( 14 )] were synthesized. According to X‐ray analysis, there were shortenings of the axial Fe? N bond lengths (up to 0.014 Å) in para‐nitro‐substituted complex 10 and (up to 0.015 Å) in meta‐nitro‐substituted complex 12 versus the Fe(II) complex without nitro groups [{o‐Me? Ph? N?C(Me)? Py? C(Me)?N? Ph? o‐Me}FeCl2 ( 1 )]. Complexes 10 , 12 , and 14 afforded very active catalysts for the production of α‐olefins and were more temperature‐stable and had longer lifetimes than parent non‐nitro‐substituted Fe(II) complex 1 . The reaction between FeCl2 and a sterically less hindered ligand [p‐NO2? Ph? N?C(Me)? Py? C(Me)?N? Ph? p‐NO2] resulted in the formation of octahedral complex 11 . A para‐dialkylamino‐substituted bis(imino)pyridine ligand [p‐NEt2? o‐Me? Ph? N?C(Me)? Py? C(Me)?N? Ph? o‐Me? p‐NEt2] and the corresponding Fe(II) complex [{p‐NEt2? o‐Me? Ph? N?C(Me)? Py? C(Me)?N? Ph? o‐Me? p‐NEt2}FeCl2 ( 16 )] were synthesized to evaluate the effect of enhanced electron donation of the ligand on the catalytic performance. According to X‐ray analysis, there was a shortening (up to 0.043 Å) of the axial Fe? N bond lengths in para‐diethylamino‐substituted complex 16 in comparison with parent Fe(II) complex 1 . © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2615–2635, 2006 相似文献
10.
Effect of ligand backbone substituents of nickel α‐diimine complexes on livingness/controllability of olefin polymerization: Competition between monomer isomerization and propagation 下载免费PDF全文
Anatolij Sokolohorskyj Robert Mundil Albena Lederer Jan Merna 《Journal of polymer science. Part A, Polymer chemistry》2016,54(19):3193-3202
Four α‐diimine nickel complexes [(Ar? N?C(R)? C(R)?N? Ar)NiBr2; R?H, CH3, cyclohexane‐1,2‐diyl, naphthalene‐1,8‐diyl, Ar?2,6‐i‐Pr2‐C6H3‐) were investigated in propene and hex‐1‐ene polymerization to identify the limits of backbone substituent R size needed to provide living/controlled α‐olefins polymerization by the sufficient suppression of β–H elimination transfer. Propagation kinetics measurements, molar mass on monomer conversion dependencies and reinitiation tests were used to evaluate the livingness of hex‐1‐ene polymerization. Interestingly, living/controlled hex‐1‐ene polymerization was observed in the case of all diimine derivatives including the one bearing only hydrogen atom in backbone positions. Unexpectedly, in the case of catalysts bearing H and CH3 backbone substituents, we observed the unusual isomerization of hex‐1‐ene into internal hexenes in parallel with its polymerization. Nevertheless, by subtracting the amount of monomer consumed in isomerization side reaction, polymerization still keeps the features of living/controlled process. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 3193–3202 相似文献
11.
Investigations of Scope and Mechanism of Nickel‐Catalyzed Transformations of Glycosyl Trichloroacetimidates to Glycosyl Trichloroacetamides and Subsequent,Atom‐Economical,One‐Step Conversion to α‐Urea‐Glycosides 下载免费PDF全文
Dr. Matthew J. McKay Nathaniel H. Park Prof. Dr. Hien M. Nguyen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(28):8691-8701
The development and mechanistic investigation of a highly stereoselective methodology for preparing α‐linked‐urea neo‐glycoconjugates and pseudo‐oligosaccharides is described. This two‐step procedure begins with the selective nickel‐catalyzed conversion of glycosyl trichloroacetimidates to the corresponding α‐trichloroacetamides. The α‐selective nature of the conversion is controlled with a cationic nickel(II) catalyst, [Ni(dppe)(OTf)2] (dppe=1,2‐bis(diphenylphosphino)ethane, OTf=triflate). Mechanistic studies have identified the coordination of the nickel catalyst with the equatorial C2‐ether functionality of the α‐glycosyl trichloroacetimidate to be paramount for achieving an α‐stereoselective transformation. A cross‐over experiment has indicated that the reaction does not proceed in an exclusively intramolecular fashion. The second step in this sequence is the direct conversion of α‐glycosyl trichloroacetamide products into the corresponding α‐urea glycosides by reacting them with a wide variety of amine nucleophiles in presence of cesium carbonate. Only α‐urea‐product formation is observed, as the reaction proceeds with complete retention of stereochemical integrity at the anomeric C?N bond. 相似文献
12.
Brian K. Long James M. Eagan Michael Mulzer Geoffrey W. Coates 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2016,128(25):7222-7226
A dibenzobarrelene‐bridged, α‐diimine NiII catalyst (rac‐ 3 ) was synthesized and shown to have exceptional behavior for the polymerization of ethylene. The catalyst afforded high molecular weight polyethylenes with narrow dispersities and degrees of branching much lower than those made by related α‐diimine nickel catalysts. Catalyst rac‐ 3 demonstrated living behavior at room temperature, produced linear polyethylene (Tm=135 °C) at −20 °C, and, most importantly, was able to copolymerize ethylene with the biorenewable polar monomer methyl 10‐undecenoate to yield highly linear ester‐functionalized polyethylene. 相似文献
13.
Bijal Kottukkal Bahuleyan Gi Wan Son Dae‐Won Park Chang‐Sik Ha Il Kim 《Journal of polymer science. Part A, Polymer chemistry》2008,46(3):1066-1082
A series of highly active ethylene polymerization catalysts based on bidendate α‐diimine ligands coordinated to nickel are reported. The ligands are prepared via the condensation of bulky ortho‐substituted anilines bearing remote push–pull substituents with acenaphthenequinone, and the precatalysts are prepared via coordination of these ligands to (DME)NiBr2 (DME = 1,2‐dimethoxyethane) to form complexes having general formula [ZN = C(An)‐C(An) = NZ]NiBr2 [Z = (4‐NH2‐3,5‐C6H2R2)2CH(4‐C6H4Y); An, acenaphthene quinone; R, Me, Et, iPr; Y = H, NO2, OCH3]. When activated with methylaluminoxane (MAO) or common alkyl aluminiums such as ethyl aluminium sesquichloride (EAS) all catalysts polymerize ethylene with activities exceeding 107 g‐PE/ mol‐Ni h atm at 30 °C and atmospheric pressure. Among the cocatalysts used EAS records the best activity. Effects of remote substituents on ethylene polymerization activity are also investigated. The change in potential of metal center induced by remote substituents, as evidenced by cyclic voltammetric measurements, influences the polymerization activity. UV–visible spectroscopic data have specified the important role of cocatalyst in the stabilization of nickel‐based active species. A tentative interpretation based on the formation of active and dormant species has been discussed. The resulting polyethylene was characterized by high molecular weight and relatively broad molecular weight distribution, and their microstructure varied with the structure of catalyst and cocatalyst. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1066–1082, 2008 相似文献
14.
Harsha D. Magurudeniya Prakash Sista Jacob K. Westbrook Taryn E. Ourso Khuong Nguyen Marie C. Maher Mussie G. Alemseghed Michael C. Biewer Mihaela C. Stefan 《Macromolecular rapid communications》2011,32(21):1748-1752
A nickel α‐diimine catalyst was used for Grignard metathesis (GRIM) polymerization of 2,5‐dibromo 3‐hexylthiophene and 2‐bromo‐5‐iodo‐3‐hexylthiophene monomers. GRIM polymerization of 2‐bromo‐5‐iodo‐3‐hexylthiophene generated regioregular polymers with molecular weights ranging from 3 000 to 12 000 g · mol−1. The nickel α‐diimine catalyst was also successfully used for the GRIM polymerization of a bulky benzodithiophene monomer.
15.
Smaranda Cota Dipl.‐Chem. Matthias Beyer Dipl.‐Chem. Rüdiger Bertermann Dr. Christian Burschka Dr. Kathrin Götz Dr. Martin Kaupp Prof. Dr. Reinhold Tacke Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(22):6582-6589
The neutral hexacoordinate silicon(IV) complex 6 (SiO2N4 skeleton) and the neutral pentacoordinate silicon(IV) complexes 7 – 11 (SiO2N2C skeletons) were synthesized from Si(NCO)4 and RSi(NCO)3 (R=Me, Ph), respectively. The compounds were structurally characterized by solid‐state NMR spectroscopy ( 6 – 11 ), solution NMR spectroscopy ( 6 and 10 ), and single‐crystal X‐ray diffraction ( 8 and 11 were studied as the solvates 8? CH3CN and 11? C5H12 ? 0.5 CH3CN, respectively). The silicon(IV) complexes 6 (octahedral Si‐coordination polyhedron) and 7 – 11 (trigonal‐bipyramidal Si‐coordination polyhedra) each contain two bidentate ligands derived from an α‐amino acid: (S)‐alanine, (S)‐phenylalanine, or (S)‐tert‐leucine. The deprotonated amino acids act as monoanionic ( 6 ) or as mono‐ and dianionic ligands ( 7 – 11 ). The experimental investigations were complemented by computational studies of the stereoisomers of 6 and 7 . 相似文献
16.
Fengshou Liu Haiyang Gao Zhilong Hu Haibin Hu Fangming Zhu Qing Wu 《Journal of polymer science. Part A, Polymer chemistry》2012,50(18):3859-3866
1‐Hexene polymerizations catalyzed by α‐diimine nickel complexes after activation with modified methylaluminoxane were performed at various reaction temperatures. Effects of catalyst structure and polymerization temperature on activity and polymer microstructure were evaluated in detail. Bulky catalyst 1b with camphyl backbone exhibited good control ability and greatly enhanced thermal stability to be capable of polymerizing 1‐hexene at 80°C. The poly(1‐hexene)s with long methylene sequences and dominate branches (methyl and butyl) were synthesized using catalyst 1b . Differential scanning calorimetry analysis further confirmed that long polymethylene block (? (CH2)n? , n > 20) was formed in the poly(1‐hexene)s with melting point of 64°C obtained by catalyst 1b on the basis of initial branched model polyethylene. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012 相似文献
17.
Xuting Wang Dr. Yanxia Zhao Shida Gong Prof. Bin Liu Prof. Qian‐Shu Li Prof. Ji‐Hu Su Prof. Biao Wu Prof. Xiao‐Juan Yang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(38):13302-13310
Reactions of the dimeric cobalt complex [(L?Co)2] ( 1 , L=[(2,6‐iPr2C6H3)NC(Me)]2) with polyarenes afforded a series of mononuclear and dinuclear complexes: [LCo(η4‐anthracene)] ( 2 ), [LCo(μ‐η4:η4‐naphthalene)CoL] ( 3 ), and [LCo(μ‐η4:η4‐phenanthrene)CoL] ( 4 ). The pyrene complexes [{Na2(Et2O)2}{LCo(μ‐η3:η3‐pyrene)CoL}] ( 5 ) and [{Na2(Et2O)3}{LCo(η3‐pyrene)}] ( 6 ) were obtained by treating precursor 1 with pyrene followed by reduction with Na metal. These complexes contain three potential redox active centers: the cobalt metal and both α‐diimine and polyarene ligands. Through a combination of X‐ray crystallography, EPR spectroscopy, magnetic susceptibility measurement, and DFT computations, the electronic configurations of these complexes were studied. It was determined that complexes 2 – 4 have a high‐spin CoI center coupled with a radical α‐diimine ligand and a neutral polyarene ligand. Whereas, the ligand L in complexes 5 and 6 has been further reduced to the dianion, the cobalt remains in a formal (I) oxidation state, and the pyrene molecule is either neutral or monoanionic. 相似文献
18.
Yi Ren Xi‐Guang Wei Si‐Jia Ren Kai‐Chung Lau Ning‐Bew Wong Wai‐Kee Li 《Journal of computational chemistry》2013,34(23):1997-2005
In order to explore the existence of α‐effect in gas‐phase SN2@N reactions, and to compare its similarity and difference with its counterpart in SN2@C reactions, we have carried out a theoretical study on the reactivity of six α‐oxy‐Nus (FO?, ClO?, BrO?, HOO?, HSO?, H2NO?) in the SN2 reactions toward NR2Cl (R = H, Me) and RCl (R = Me, i‐Pr) using the G2(+)M theory. An enhanced reactivity induced by the α‐atom is found in all examined systems. The magnitude of the α‐effect in the reactions of NR2Cl (R = H, Me) is generally smaller than that in the corresponding SN2 reaction, but their variation trend with the identity of α‐atom is very similar. The origin of the α‐effect of the SN2@N reactions is discussed in terms of activation strain analysis and thermodynamic analysis, indicating that the α‐effect in the SN2@N reactions largely arises from transition state stabilization, and the “hyper‐reactivity” of these α‐Nus is also accompanied by an enhanced thermodynamic stability of products from the n(N) → σ*(O?Y) negative hyperconjugation. Meanwhile, it is found that the reactivity of oxy‐Nus in the SN2 reactions toward NMe2Cl is lower than toward i‐PrCl, which is different from previous experiments, that is, the SN2 reactions of NH2Cl is more facile than MeCl. © 2013 Wiley Periodicals, Inc. 相似文献
19.
Self‐immobilized nickel and iron diimine catalysts bearing one or two allyl groups of [ArN?C]2(C10H6)NiBr2 [Ar = 4‐allyl‐2,6‐(i‐Pr)2C6H2] ( 1 ), [ArN?C(Me)][Ar′N? C(Me)]C5H3NFeCl2 [Ar = Ar′ = 4‐allyl‐2,6‐(i‐Pr)2C6H3, Ar = 2,6‐(i‐Pr)2C6H3, and Ar′ = 4‐allyl‐2,6‐(i‐Pr)2C6H3] were synthesized and characterized. All three catalysts were investigated for olefin polymerization. As a result, these catalysts not only showed high activities as the catalyst free from the allyl group, such as [ArN?C]2C10H6NiBr2 (Ar = 2,6‐(i‐Pr)2C6H2)], but also greatly improved the morphology of polymer particles to afford micron‐granula polyolefin. The self‐immobilization of catalysts, the formation mechanism of microspherical polymer, and the influence on the size of the particles are discussed. The molecular structure of self‐immobilized nickel catalyst 1 was also characterized by crystallographic analysis. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1018–1024, 2004 相似文献
20.
Ping Huo Wanyun Liu Xiaohui He Yiwang Chen 《Journal of polymer science. Part A, Polymer chemistry》2014,52(22):3213-3220
The covalently immobilized multiwalled carbon nanotubes (MWNTs) supported three‐dimensional geometry α‐diimine nickel, palladium catalysts are prepared by corresponding α‐diimine nickel, palladium complexes and activated MWNTs. The molecular structures of the catalysts have been confirmed by X‐ray single‐crystal analyses, NMR and XPS, as well as elemental analysis. Compared with nickel, palladium catalysts without modification and physical mixing of nickel, palladium catalysts with MWNTs, the MWNTs supported nickel, palladium catalysts show improved activity and productivity in norbornene homopolymerization and copolymerization with polar monomer. The morphology of the resulting polymers obtained from MWNTs‐supported nickel(II) complex reveals that the MWNTs are dispersed uniformly in polymer and wrapped by polymers to squeeze out of spherical particles, leading to the enhanced processability and mechanical properties. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 3213–3220 相似文献