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1.
Hoang The Ban Toshiya Uozumi Kazuo Soga 《Journal of polymer science. Part A, Polymer chemistry》1998,36(13):2269-2274
Both the rac- and meso-dinuclear ansa-zirconocene catalysts (μ-C12H8{[SiPh(Ind)2]ZrCl2}2) were prepared by a coupling reaction between 2 equiv of diindenylphenylchlorosilane (rac- and meso-isomers) and 1 equiv of p-dilithiobiphenyl in diethyl ether at −80°C, followed by a successive reaction with ZrCl4 · 2THF in THF at −78°C. Polymerizations of ethene and propene were conducted in a 1 dm3 high-pressure glass reactor equipped with a mechanical stirrer at 60, 80, 100, 120, and 150°C using methylalumoxane (MAO) as cocatalyst and toluene or decahydronaphthalene as the solvent. Copolymerization of ethene and 1-octene was also checked in brief. For ethene polymerization, the meso-catalyst was found to be more active, which displayed an extremely high activity to give linear polyethene with a high molecular weight and a narrow molar mass distribution (MMD). The apparent activity increased monotonously with rising polymerization temperature from 60°C up to 150°C, indicating that the active species are stable even at a high temperature. On the other hand, both the rac- and meso-catalysts showed very poor activities for propene polymerization. However, copolymerization of ethene and 1-octene proceeded at a high speed. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2269–2274, 1998 相似文献
2.
Andreas Kapelski Jun Okuda 《Journal of polymer science. Part A, Polymer chemistry》2013,51(23):4983-4991
Ring‐opening polymerization of rac‐ and meso‐lactide initiated by indium bis(phenolate) isopropoxides {1,4‐dithiabutanediylbis(4,6‐di‐tert‐butylphenolate)}(isopropoxy)indium ( 1 ) and {1,4‐dithiabutanediylbis(4,6‐di(2‐phenyl‐2‐propyl)phenolate)}(isopropoxy)indium ( 2 ) is found to follow first‐order kinetics for monomer conversion. Activation parameters ΔH? and ΔS? suggest an ordered transition state. Initiators 1 and 2 polymerize meso‐lactide faster than rac‐lactide. In general, compound 2 with the more bulky cumyl ortho‐substituents in the phenolate moiety shows higher polymerization activity than 1 with tert‐butyl substituents. meso‐Lactide is polymerized to syndiotactic poly(meso‐lactides) in THF, while polymerization of rac‐lactide in THF gives atactic poly(rac‐lactides) with solvent‐dependent preferences for heterotactic (THF) or isotactic (CH2Cl2) sequences. Indium bis(phenolate) compound rac‐(1,2‐cyclohexanedithio‐2,2′‐bis{4,6‐di(2‐phenyl‐2‐propyl)phenolato}(isopropoxy)indium ( 3 ) polymerizes meso‐lactide to give syndiotactic poly(meso‐lactide) with narrow molecular weight distributions and rac‐lactide in THF to give heterotactically enriched poly(rac‐lactides). © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4983–4991 相似文献
3.
Oxidative Aryl-Aryl-Coupling of 6,6′,7,7′-Tetramethoxy-1,1′,2,2′,3,3′,4,4′-octahydro-1,1′-biisoquinoline Derivatives We describe the synthesis of 2 by intramolecular oxidative coupling of 1, 1′-biisoquinoline derivatives 1 (Scheme 1). This heterocyclic system can be considered as a union of two apomorphine molecules and may thus exhibit dopaminergic activity. - The readily available tetrahydrobiisoquinoline 6 was methylated to 11 (Scheme 4) and reduced (with NaBH3CN) to rac- 7 and (catalytically) to meso- 7 (Scheme 3). Reduction of 11 with NaBH4 and of the biurethane rac- 9 with LiAlH4/AlCl3 afforded meso- and rac- 10 , respectively (Scheme 4). Demethylation of 6 , meso- 10 , meso- and rac- 7 led to 12 , meso- 14 , meso- and rac- 13 , respectively (Scheme 5). The latter two phenols were converted with chloroformic ester to the hexaethoxycarbonyl derivatives meso- and rac- 15 and subsequently saponified to the biurethanes meso- and rac- 16 , respectively (Scheme 5). - In order to assure proximity of the two aromatic rings, the ethano-bridged derivatives meso- and rac- 18 were prepared by condensing meso- and rac- 7 with oxalic ester and reducing the oxalyl derivatives meso- and rac- 17 with LiAlH4/AlCl3, respectively (Scheme 6). The 1H-NMR, spectra at different temperatures showed that rac- 18 populated two conformers but rac- 17 only one, all with C2-symmetry, and that meso- 17 as well as meso- 18 populated two enantiomeric conformers with C1-symmetry. Whereas both oxalyl derivatives 17 were fairly rigid due to the two amide groupings, the ethano derivatives 18 exhibited coalescence temperatures of -20 and 30°. - The intramolecular coupling of the two aromatic rings was successful under ‘non-phenolic oxidative’ conditions with the tetramethoxy derivatives 7, 10 and 18 , the rac-isomers leading to the desired dibenzophenanthrolines, the meso-isomers, however, mostly to dienones (Scheme 9): With VOF3 and FSO3H in CF3COOH/CH2Cl2 rac- 7 was converted to rac- 19 , rac- 18 to rac- 21 and rac- 10 to a mixture of rac- 20 and the dienone 23b of the morphinane type. Under the same conditions meso- 10 was transformed to the dienone 23a of the morphinane type, whereas meso- 18 yielded the dienone 24 of the neospirine type, both in lower yields. The analysis of the spectral data of the six coupling products offers evidence for their structures. With the demethylation of rac- 20 and rac- 21 to rac- 25 and rac- 26 , respectively, the synthetic goal of the work was reached, but only in the rac-series (Scheme 10). - In the course of this work two cleavages of octahydro-1,1′-biisoquinolines at the C(1), C(1′)-bond were observed: (1) The biurethanes 9 and 16 in both the meso- and rac-series reacted with oxygen in CF3COOH solution to give the 3,4-dihydroisoquinolinium salts 27 and 28 ; the latter was deprotonated to the quinomethide 30 (Scheme 11). (2) Under the Clarke-Eschweiler reductive-methylation conditions meso- and rac- 7 were cleaved to the tetrahydroisoquinoline derivative 32 . 相似文献
4.
A series of unsymmetrical complexes of 2,3-bis(2-phenylphenyl)-butanediimine nickel(II) dibromide (complex 1), 1,4-bis(2-isopropyl-6-methylphenyl)-acenaphthenediimine nickel(II) dibromide (complex 2) and meso- and rac-1,4-bis (2,4-di-tert-butyl-6-methylphenyl)-acenaphthenediimine nickel(II) dibromide (meso-3 and rac-3) were synthesized and activated by methylaluminoxane (MAO) for ethylene polymerization. By 13C NMR characterization, meso- and rac-stereo-isomers were detected in the condensation products resulting from the reaction of unsym-substituted anilines with diketones. It was notable that meso- and rac-isomers in ligand 1 or ligand 2 could not be separated owing to their interconversion, however, meso- and rac-isomers in ligand 3 could be isolated and identified by X-ray diffraction and NMR analysis. At low polymerization temperatures, complex 1/MAO afforded polyethylene with bimodal molecular weight distribution, while complex 2/MAO prepared polyethylene with single-modal distribution. Moreover, by raising polymerization temperature or extending time of catalyst aging, bimodal molecular weight distribution polyethylene was also produced by complex 2/MAO. The hypothesis of bimodal molecular weight distribution polyethylene synthesized by unsymmetrical α-diimine nickel(II) complexes was supported that the molecular weight of polyethylene produced by rac-3/MAO was significantly higher than that produced by meso-3/MAO under identical polymerization conditions. A unique methodology to prepare polyethylene with bimodal molecular weight distribution was demonstrated. 相似文献
5.
R. F. Storey B. D. Mullen G. S. Desai J. W. Sherman C. N. Tang 《Journal of polymer science. Part A, Polymer chemistry》2002,40(20):3434-3442
Polyesters and poly(ester carbonates) were synthesized via ring‐opening polymerization with new tin(II) macroinitiator adducts containing oligomeric L ‐lactide (LLA), rac‐lactide (rac‐LA), and ?‐caprolactone (CL). The novel initiating species were synthesized by the reaction of LLA, rac‐LA, or CL with Sn(OEt)2 (monomer concentration/initiator concentration ≤20) and then were dissolved in methylene chloride or toluene and stored in a stoppered flask for the subsequent ring‐opening polymerization of cyclic esters and carbonates. The soluble tin alkoxide macroinitiators yielded predictable and quantitative initiation of polymerization for up to 1 month of storage time at room temperature. The resulting polymers displayed low polydispersity (≤1.5), and a high monomer conversion (>95%) was obtained within relatively short polymerization times (≤2 h). Adjusting the monomer/macroinitiator ratio effectively controlled the molecular weights of the polymers. NMR was used to characterize the initiating species and polymer microstructure, and size exclusion chromatography was used to determine the molecular weight properties of the polymers. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3434–3442, 2002 相似文献
6.
Nedorezova P. M. Aladyshev A. M. Savinov D. V. Veksler E. N. Tsvetkova V. I. Lemenovskii D. A. 《Kinetics and Catalysis》2003,44(3):311-318
The effects of various pathways of the formation of catalytic systems based on the rac-Me2SiInd2ZrCl2 metallocene on the activity and properties of polypropylene prepared by the bulk polymerization of propylene were studied in detail. It was found that the conditions of formation of the catalytic system affect not only its activity and the character of kinetic curves but also the molecular weight of the synthesized polymer. Propylene polymerization was studied with the use of a number of bisindenyl derivatives of zirconium, which were mixtures of rac and meso forms that differ in the nature of substituents in the Si bridge or the indenyl ligand. The conclusion was drawn that, with the use of metallocenes as a mixture of rac and meso forms, high-molecular-weight isotactic polypropylene can be prepared with high stereoregularity at a very high rate; thereby, the stage of separation of a pure rac isomer can be excluded in the synthesis of the catalyst. 相似文献
7.
Sarah E. Reybuck Robert M. Waymouth 《Journal of polymer science. Part A, Polymer chemistry》2004,42(13):3323-3331
Ethylene/1‐hexene copolymerizations with disiloxane‐bridged metallocenes, rac‐ and meso‐1,1,3,3‐tetramethyldisiloxanediyl‐bis(1‐indenyl)zirconium dichloride (rac‐ 1 , meso‐ 1 ) activated by modified methylaluminoxane were performed to investigate the influence of conformational dynamics on comonomer selectivity. Although 1H NOESY (nuclear Overhauser and exchange spectroscopy) analysis indicated that the most stable conformation for the meso isomer in solution was that in which both indenes project over the metal coordination site, this isomer showed higher 1‐hexene selectivity in copolymerization (re = 140 ± 30, rh = 0.024 ± 0.004) than the rac isomer with only one indene over the coordination site (re = 240 ± 20, rh = 0.005 ± 0.001). The meso isomer showed high 1‐hexene selectivity, a high product of reactivity ratios (rerh = 3.3 ± 0.5) and produced copolymers that could be separated into fractions with different ethylene content suggesting that the active species exhibited multisite behavior and populated conformations with different comonomer selectivities during the copolymerization. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3323–3331, 2004 相似文献
8.
Abstract The kinetics of propylene polymerization initiated by racemic ethylene-1,2-bis(1-indenyl) zirconium bis(dimethylamide) [rac-(EBI) Zr(NMe2)2(rac-1)] cocatalyzed by methylaluminoxane (MAO) were studied. The polymerization behaviors of rac-1/MAO catalyst investigated by changing various experimental parameters are quite different from those of rac-(EBI) ZrCl2 (rac-2)/MAO catalyst, due to the differences in the generation procedure of cationic actives species of each metallocene by the reaction with MAO. The activity of rac-1/MAO catalyst showed maximum when [Al]/[Zr] is around 2000, when [Zr] is 137.1 μM, and when polymerization temperature is 30°C. The negligible activity of rac-1/MAO catalyst at a very low MAO concentration seems to be caused by the instability of the cationic active species. The meso pentad values of polymers produced by rac-1/MAO catalyst at 30°C are in the range of 82.8% to 89.7%. The rac-1/MAO catalyst lost stereorigid character at the polymerization temperature above 60°C. The molecular weight of polymer decreased as [Al]/[Zr] ratio, polymerization temperature, and [Zr] increased. The molecular weight distributions of all polymers are in the range of 1.8–2.3, demonstrating uniform active species present in the polymerization system. 相似文献
9.
Yoshitaka Yamaguchi Noriyuki Suzuki Arno Fries Takaya Mise Hiroyuki Koshino Yuji Ikegami Hiromichi Ohmori Akira Matsumoto 《Journal of polymer science. Part A, Polymer chemistry》1999,37(3):283-292
Stereospecific polymerization of 1‐hexene under high pressures (up to 1,000 MPa = ca. 10,000 atm) using metallocene/methylaluminoxane (MAO) catalysts was investigated. Several C2‐symmetric ansa‐metallocenes, their meso‐isomers, and two Cs‐symmetric ansa‐metallocenes were employed as catalyst precursors. In the course of this study, novel C2‐symmetric germylene‐bridged ansa‐metallocenes, (rac‐[Me2Ge(η5‐C5H‐2,3,5‐Me3)2MCl2] (M = Zr, rac‐4a; M = Hf, rac‐4b), have been prepared. High pressures induced enhancement of the catalytic activity and the molecular weight of the polymers in most of the catalysts. The maximum of both the catalytic activity and the molecular weight of the polymers was mostly observed at 100–500 MPa in each catalyst, although the enhanced ratio was smaller than that observed for nonbridged metallocenes. Isospecificity of the C2‐symmetric ansa‐metallocene catalysts was essentially maintained even under high pressure. Highly isotactic polyhexene ([mmmm] = 91.6%) with very high molecular weight (Mw = 2,360,000) was achieved by rac‐4b under 250 MPa. High pressures slightly decreased syndiotacticity when the Cs‐symmetric ansa‐metallocene, isopropylidene(1‐η5‐cyclopentadienyl)(9‐η5‐fluorenyl)zirconium dichloride 5, was employed. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 283–292, 1999 相似文献
10.
Johannes Carolus Jansen Raniero Mendichi Paolo Locatelli Incoronata Tritto 《Macromolecular rapid communications》2001,22(17):1394-1398
The kinetics of the ethylene‐norbornene copolymerization, catalyzed by rac‐Et(Ind)2ZrCl2/MAO, 90%rac/10%meso‐Et(4,7‐Me2Ind)2ZrCl2/MAO and rac‐H2C(3‐tert‐BuInd)2ZrCl2/MAO was followed by sampling from the reaction mixture at fixed time intervals. Catalyst activity, copolymer composition and molar mass were studied as a function of time. The polymers showed an unusually low polydispersity and a significant increase in their molar mass with time, suggesting a quasi‐living polymerization. 相似文献
11.
Tanja Seraidaris Arto Puranen Mikko Karesoja Barbro Lfgren Timo Repo Markku Leskel Jukka Seppl 《Journal of polymer science. Part A, Polymer chemistry》2006,44(16):4743-4751
Elastic polypropene has gained growing industrial and academic interest as a thermoplastic elastomer. In this study, “rac”‐ and “meso”‐dimethylsilyl(3‐benzylindenyl)(2‐methylindenyl)hafnium dichloride complexes (Hfr and Hfm, respectively), activated with [NHMe2Ph][B(C6F5)4]/triisobutyl aluminum, were used in propene polymerization. Using these catalyst systems, we obtained polymers with high molar masses, up to 550 kg/mol, and moderate isotacticities between 34 and 52%. By varying the polymerization conditions, we could modify the polymer microstructure and molar mass. 13C NMR was used to calculate the polymer pentad sequence distributions. The crystalline parts of the polymers were analyzed with the differential scanning calorimetry successive self‐nucleation and annealing (SSA) technique. The SSA thermograms revealed that Hfr produced polypropene with a more uniform lamellar structure than Hfm. The mechanical properties were tested with dynamic mechanical analysis creep‐recovery tests. In the series, the polymers with the lowest isotacticities and therefore lowest crystallinities showed the best elastic properties. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4743–4751, 2006 相似文献
12.
David S. McGuinness Edward L. Marshall Vernon C. Gibson Jonathan W. Steed 《Journal of polymer science. Part A, Polymer chemistry》2003,41(23):3798-3803
Hetero‐bimetallic Fe(II) alkoxide/aryloxides were evaluated as initiators for the ring‐opening polymerization of rac‐lactide. [(THF)NaFe(OtBu)3]2 ( 1 ) and [(THF)4Na2Fe(2,6‐diisopropylphenolate)4] ( 2 ) (THF = tetrahydrofuran) both polymerized lactide efficiently at room temperature, with complex 1 affording better control over the molecular weight parameters of the resultant polymer. At conversions below 70%, a linear increase in molecular weight with conversion was observed, indicative of a well‐controlled polymerization process. Complex 2 is the first example of a dianionic Fe(II) alkoxide and has been structurally characterized to reveal a distorted square planar FeO4 array in which both Na counterions bridge two aryloxide ligands and are further complexed by two THF ligands. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3798–3803, 2003 相似文献
13.
Everta Keren Govindarajan Sundararajan 《Journal of polymer science. Part A, Polymer chemistry》2007,45(16):3599-3610
The 2‐[benzyl‐(2‐hydroxy‐2‐phenylethyl)‐amino]‐1‐phenylethanol ligand (1‐H2) prepared as a diastereomeric mixture or in racemic and meso forms, from known procedure, has been disodiated and complexed with ZrCl4. The precatalysts (mix‐1‐ZrCl2, rac‐1‐ZrCl2, and meso‐1‐ZrCl2) were used in combination with methylaluminoxane and found to be active for the polymerization of 1‐hexene and 1‐octene. The high molecular weight polyhexenes (PHs) and polyoctenes (POs) thus obtained were isotactic in nature and showed a negligible amount of end groups arising from the chain termination reactions. In PHs and POs, there was linear correlation in the modified Arrhenius plot (the natural logarithm of the number‐average molecular weight vs. the reciprocal of the temperature), indicating the presence of a single active species. The enantiomerically pure titanium precatalyst ((R,R)‐1‐TiCl2), when employed for the polymerization of 1‐hexene, was found to be active and the modified Arrhenius plot showed linear dependence demonstrating presence of a single active species. The analogous titanium precatalysts (mix‐1‐TiCl2, rac‐1‐TiCl2, and meso‐1‐TiCl2) obtained from known procedures were also found to be active for the polymerization of 1‐octene. The rac‐1‐TiCl2 precatalyst demonstrated a sigmoidal behavior in the modified Arrhenius plot for the POs and the mix‐1‐TiCl2 precatalyst showed an exponential type of behavior. The obtained POs seemed to have small amounts of chain termination via β‐hydride elimination alone. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3599–3610, 2007 相似文献
14.
Propene, 1-butene and 1-hexene polymerization was conducted with a mixture of rac- and meso-[dimethylsilylenebis((2,3,5-tetramethyl-cyclopentadienyl))]zirconium dichloride (Me2Si(2,3,5-Me3Cp)2ZrCl2) ( 1 ) combined with methylaluminoxane (MAO), triethylaluminium (AlEt3)/triphenylcarbenium tetrakis(pentafluorophenyl)borate (Ph3CB(C6F5)4) ( 2 ) and triisobutylaluminium (AliBu3)/Ph3CB(C6F5)4, respectively, as co-catalyst systems. The ratios of polymerization rates Rp(rac)/Rp(meso) were changed with the combined cocatalysts. It was found that in the case of using trialkylaluminium/ 2 as co-catalyst Rp(rac)/Rp(meso) is lower than when using MAO in any kind of α-olefin polymerization. 相似文献
15.
Wentian Lin Hui Niu T. C. Mike Chung Jin‐Yong Dong 《Journal of polymer science. Part A, Polymer chemistry》2010,48(16):3534-3541
This article discusses a new borane chain transfer reaction in olefin polymerization that uses trialkylboranes as a chain transfer agent and thus can be realized in conventional single site polymerization processes under mild conditions. Commercially available triethylborane (TEB) and synthesized methyl‐B‐9‐borabicyclononane (Me‐B‐9‐BBN) were engaged in metallocene/MAO [depleted of trimethylaluminum (TMA)]‐catalyzed ethylene (Cp2ZrCl2 and rac‐Me2Si(2‐Me‐4‐Ph)2ZrCl2 as a catalyst) and styrene (Cp*Ti(OMe)3 as catalyst) polymerizations. The two trialkylboranes were found—in most cases—able to initiate an effective chain transfer reaction, which resulted in hydroxyl (OH)‐terminated PE and s‐PS polymers after an oxidative workup process, suggesting the formation of the B‐polymer bond at the polymer chain end. However, chain transfer efficiencies were influenced substantially by the steric hindrances of both the substituent on the trialkylborane and that on the catalyst ligand. TEB was more effective than TMA in ethylene polymerization with Cp2ZrCl2/MAO, whereas it became less effective when the catalyst changed to rac‐Me2Si(2‐Me‐4‐Ph)2ZrCl2. Both TEB and Me‐B‐9‐BBN caused an efficient chain transfer in the Cp2ZrCl2/MAO‐catalyzed ethylene polymerization; nevertheless, Me‐B‐9‐BBN failed in vain with rac‐Me2Si(2‐Me‐4‐Ph)2ZrCl2/MAO. In the case of styrene polymerization with Cp*Ti(OMe)3/MAO, thanks to the large steric openness of the catalyst, TEB exhibited a high efficiency of chain transfer. Overall, trialkylboranes as chain transfer agents perform as well as B? H‐bearing borane derivatives, and are additionally advantaged by a much milder reaction condition, which further boosts their applicability in the preparation of borane‐terminated polyolefins. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3534–3541, 2010 相似文献
16.
Hideaki Ishizawa Tamaki Nakano Tohru Yade Masashi Tsuji Osamu Nakagawa Takashi Yamaguchi 《Journal of polymer science. Part A, Polymer chemistry》2004,42(18):4656-4665
Poly(9-fluoreneyl methacrylate) was obtained through anionic polymerization with t-BuLi and t-BuMgBr and through radical polymerization with α,α′-azobisisobutyronitrile. Anionic polymerization with t-BuLi in tetrahydrofuran and radical polymerization afforded syndiotactic polymers (rr ∼ 90%), whereas anionic polymerization with Li and Mg initiators in toluene and CH2Cl2 led to isotactic polymers. The thermal and photophysical properties of the polymers were examined. A syndiotactic polymer tended to show higher glass transition and decomposition temperatures than an isotactic polymer. However, polymers with different tacticities were not likely to assume specific, distinctive conformations such as a helix or a π-stacked conformation in solution. An isotactic polymer showed stronger interactions in a CH2Cl2 solution with 2,4,7-trinitro-9-fluorenylidenemalononitrile, an electron-acceptor molecule, than a syndiotactic polymer. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4656–4665, 2004 相似文献
17.
Strongly Luminous Tetranuclear Gold(I) Complexes Supported by Tetraphosphine Ligands,meso‐ or rac‐Bis[(diphenylphosphinomethyl)phenylphosphino]methane
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Prof. Tomoaki Tanase Risa Otaki Tomoko Nishida Hiroe Takenaka Dr. Yukie Takemura Prof. Bunsho Kure Prof. Takayuki Nakajima Prof. Yasutaka Kitagawa Prof. Taro Tsubomura 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(6):1577-1596
A series of tetragold(I) complexes supported by tetraphosphine ligands, meso‐ and rac‐bis[(diphenylphosphinomethyl)phenylphosphino]methane (meso‐ and rac‐dpmppm) were synthesized and characterized to show that the tetranuclear AuI alignment varies depending on syn‐ and anti‐arrangements of the two dpmppm ligands with respect to the metal chain. The structures of syn‐[Au4(meso‐dpmppm)2X]X′3 (X=Cl; X′=Cl ( 4 a ), PF6 ( 4 b ), BF4 ( 4 c )) and syn‐[Au4(meso‐dpmppm)2]X4 (X=PF6 ( 4 d ), BF4 ( 4 e ), TfO ( 4 f ); TfO=triflate) involved a bent tetragold(I) core with a counter anion X incorporated into the bent pocket. Complexes anti‐[Au4(meso‐dpmppm)2]X4 (X=PF6 ( 5 d ), BF4 ( 5 e ), TfO ( 5 f )) contain a linearly ordered Au4 string and complexes syn‐[Au4(rac‐dpmppm)2X2]X′2 (X=Cl, X′=Cl ( 6 a ), PF6 ( 6 b ), BF4 ( 6 c )) and syn‐[Au4(rac‐dpmppm)2]X4 (X=PF6 ( 6 d ), BF4 ( 6 e ), TfO ( 6 f )) consist of a zigzag tetragold(I) chain supported by the two syn‐arranged rac‐dpmppm ligands. Complexes 4 d–f , 5 d–f , and 6 d–f with non‐coordinative large anions are strongly luminescent in the solid state (λmax=475–515 nm, Φ=0.67–0.85) and in acetonitrile (λmax=491–520 nm, Φ=0.33–0.97); the emission was assigned to phosphorescence from 3[dσ*σ*σ*pσσσ] excited state of the Au4 centers on the basis of DFT calculations as well as the long lifetime (a few μs). The emission energy is predominantly determined by the HOMO and LUMO characters of the Au4 centers, which depend on the bent ( 4 ), linear ( 5 ), and zigzag ( 6 ) alignments. The strong emissions in acetonitrile were quenched by chloride anions through simultaneous dynamic and static quenching processes, in which static binding of chloride ions to the Au4 excited species should be the most effective. The present study demonstrates that the structures of linear tetranuclear gold(I) chains can be modified by utilizing the stereoisomeric tetraphosphines, meso‐ and rac‐dpmppm, which may lead to fine tuning of the strongly luminescent properties intrinsic to the AuI4 cluster centers. 相似文献
18.
We report the polymerization of phenyl isocyanides with the chiral palladium(II) initiating system. The resulting polymers with optically active properties were obtained by polymerization of the racemic isocyanide monomer (rac-1), and enantiomerically unbalanced polymerization of the monomer was found, providing substantial evidence for the enantiomer-selective polymerization of rac-1 mediated through chiral catalyst. A comparison between the enantiomerically pure monomers, 4-isocyanobenzoyl-L-alanine decyl ester (1s) and 4-isocyanobenzoyl-D-alanine decyl ester (1r), revealed a drastic discrepancy in the reactivity ratio of their homopolymerizations. It turned out that the monomer reactivity ratio of 1s was higher than that of 1r with chiral ligands. The results clearly demonstrated the inclination for incorporation of the 1s enantiomer during the polymerization process and thus resulted in the enantiomer-selective polymerization in this system. The effects of the catalyst chirality on the optically active properties of polymerization were investigated, and it was concluded that the formation of higher-ordered conformation with a handed helicity might be attributed to the chiral induction of chiral palladium(II) catalyst. Moreover, the polymers obtained through the enantiomer-selective polymerization of the enantiomerically pure monomer were with a significant improvement of the optical activity if the chirality of the monomer and the catalyst matched with each other. 相似文献
19.
Hui‐Ju Chuang Hsiao‐Li Chen Jian‐Li Ye Zn‐Yun Chen Pei‐Ling Huang Tzu‐Ting Liao Tsung‐En Tsai Chu‐Chieh Lin 《Journal of polymer science. Part A, Polymer chemistry》2013,51(3):696-707
A series of magnesium benzylalkoxide complexes, [LnMg(μ‐OBn)]2 ( 1 – 14 ) supported by NNO‐tridentate pyrazolonate ligands with various electron withdrawing‐donating subsituents have been synthesized and characterized. X‐ray crystal structural studies revealed that Complexes 1 – 3 , 5 , 7 , 9 , and 10 are dinuclear bridging through benzylalkoxy oxygen atoms with penta‐coordinated metal centers. All of these complexes acted as efficient initiators for the ring‐opening polymerization of L‐lactide and rac‐lactide. Based on kinetic studies, the activity of these metal complexes is significantly influenced by the electronic effect of the ancillary ligands with the electron‐donating substituents at the phenyl rings enhancing the polymerization rate. In addition, the “living” and “immortal” character of 6 has paved a way to synthesize as much as 40‐fold polymer chains of polylactides with a very narrow polydispersity index in the presence of a small amount of initiator. Among all of magnesium complexes, Complex 6 exhibits the highest stereoselectivity toward ring‐opening polymerization of rac‐lactide with Pr up to 88% in THF at 0 °C. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013 相似文献
20.
Dr. Tomer Rosen Dr. Jitendrasingh Rajpurohit Dr. Sophia Lipstman Prof. Vincenzo Venditto Prof. Moshe Kol 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(71):17183-17189
The coordination chemistry and the activities in the ring-opening polymerization catalysis of racemic lactide (LA) of magnesium complexes of a series of {ONNN}-type sequential monoanionic ligands are described. All ligands include pyridyl and substituted-phenolate as peripheral groups. The ligands bearing either chiral or meso-bipyrrolidine cores led to single diastereomeric complexes, whereas the ligands bearing a diaminoethane core led to diastereomer mixtures. All {ONNN}Mg-X complexes [X=Cl, HMDS (hexamethyldisilazide)] led to highly active and isoselective catalysts. The complexes bearing the chiral bipyrrolidine core exhibited the highest activities (full consumption of 5000 equiv. of rac-LA at RT within 5 min) and highest isoselectivities (Pm=0.91), as well as a living character. The complexes of the meso-bipyrrolidine based ligands were almost as active and slightly less stereoselective, while those of the diaminoethane based ligands exhibited reduced activities and isoselectivities. 相似文献