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1.
Mayilmurugan R Harum BN Volpe M Sax AF Palaniandavar M Mösch-Zanetti NC 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(2):704-713
The asymmetric molybdenum(VI) dioxo complexes of the bis(phenolate) ligands 1,4‐bis(2‐hydroxybenzyl)‐1,4‐diazepane, 1,4‐bis(2‐hydroxy‐4‐methylbenzyl)‐1,4‐diazepane, 1,4‐bis(2‐hydroxy‐3,5‐dimethylbenzyl)‐1,4‐diazepane, 1,4‐bis(2‐hydroxy‐3,5‐di‐tert‐butylbenzyl)‐1,4‐diazepane, 1,4‐bis(2‐hydroxy‐4‐flurobenzyl)‐1,4‐diazepane, and 1,4‐bis(2‐hydroxy‐4‐chlorobenzyl)‐1,4‐diazepane (H2(L1)–H2(L6), respectively) have been isolated and studied as functional models for molybdenum oxotransferase enzymes. These complexes have been characterized as asymmetric complexes of type [MoO2(L)] 1–6 by using NMR spectroscopy, mass spectrometry, elemental analysis, and electrochemical methods. The molecular structures of [MoO2(L)] 1–4 have been successfully determined by single‐crystal X‐ray diffraction analyses, which show them to exhibit a distorted octahedral coordination geometry around molybdenum(VI) in an asymmetrical cis‐β configuration. The Mo? Ooxo bond lengths differ only by ≈0.01 Å. Complexes 1 , 2 , 5 , and 6 exhibit two successive MoVI/MoV (E1/2, ?1.141 to ?1.848 V) and MoV/MoIV (E1/2, ?1.531 to ?2.114 V) redox processes. However, only the MoVI/MoV redox couple was observed for 3 and 4 , suggesting that the subsequent reduction of the molybdenum(V) species is difficult. Complexes 1 , 2 , 5 , and 6 elicit efficient catalytic oxygen‐atom transfer (OAT) from dimethylsulfoxide (DMSO) to PMe3 at 65 °C at a significantly faster rate than the symmetric molybdenum(VI) complexes of the analogous linear bis(phenolate) ligands known so far to exhibit OAT reactions at a higher temperature (130 °C). However, complexes 3 and 4 fail to perform the OAT reaction from DMSO to PMe3 at 65 °C. DFT/B3LYP calculations on the OAT mechanism reveal a strong trans effect. 相似文献
2.
《International journal of quantum chemistry》2018,118(10)
•OH addition reactions play a pivotal role in the atmospheric transformation of a number of phenyl and substituted phenyl‐based persistent and toxic organic pollutants. Here, we screened appropriate DFT functionals to predict reaction mechanisms and rate constants (kOH) of the •OH additions by taking benzene and substituted benzenes (C6H5F, C6H5Cl, C6H5Br, C6H5CH3, C6H5OH) as model compounds. By comparing the kOH values calculated with DFT methods to experimental values, we found that the ωB97 functional is the best among the 18 functionals considered (using the basis sets 6‐31 + G(d,p) for optimizations and 6‐311++G(3df,2pd) for single point energy calculations) in the temperature range of 230‐330 K. In addition, we found that some other functionals performed well in specific conditions, e.g., BMKD3 is good for benzene, halogenated benzenes and C6H5CH3, and CAM‐B3LYP is good for the reaction of C6H5OH at room temperature. Based on the diversity of the electronic structures of the selected model compounds and the frequent occurrence of certain substituents ( CH3, OH, F, Cl, and Br) in the target compounds, the functionals recommended here can be used for future study of the reaction mechanisms and kOH values for •OH addition to phenyl and substituted phenyl‐based persistent and toxic organic pollutants. 相似文献
3.
Marte Sofie Martinsen Holmsen Ainara Nova Sigurd
ien‐
degaard Richard H. Heyn Mats Tilset 《Angewandte Chemie (International ed. in English)》2020,59(4):1516-1520
A highly asymmetric AuIII η3‐allyl complex has been generated by treating Au(η1‐allyl)Br(tpy) (tpy=2‐(p‐tolyl)pyridine) with AgNTf2. The resulting η3‐allyl complex has been characterized by NMR spectroscopy and X‐ray crystallography. DFT calculations and variable temperature 1H NMR suggest that the allyl ligand is highly fluxional. 相似文献
4.
Pyridyl‐Functionalised 3H‐1,2,3,4‐Triazaphospholes: Synthesis,Coordination Chemistry and Photophysical Properties of Low‐Coordinate Phosphorus Compounds
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Julian A. W. Sklorz Santina Hoof Nadine Rades Dr. Nicolas De Rycke László Könczöl Dr. Dénes Szieberth Manuela Weber Dr. Jelena Wiecko Prof. Dr. László Nyulászi Prof. Dr. Muriel Hissler Prof. Dr. Christian Müller 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(31):11096-11109
Novel conjugated, pyridyl‐functionalised triazaphospholes with either tBu or SiMe3 substituents at the 5‐position of the N3PC heterocycle have been prepared by a [3+2] cycloaddition reaction and compared with structurally related, triazole‐based systems. Photoexcitation of the 2‐pyridyl‐substituted triazaphosphole gives rise to a significant fluorescence emission with a quantum yield of up to 12 %. In contrast, the all‐nitrogen triazole analogue shows no emission at all. DFT calculations indicate that the 2‐pyridyl substituted systems have a more rigid and planar structure than their 3‐ and 4‐pyridyl isomers. Time‐dependent (TD) DFT calculations show that only the 2‐pyridyl‐substituted triazaphosphole exhibits similar planar geometry, with matching conformational arrangements in the lowest energy excited state and the ground state; this helps to explain the enhanced emission intensity. The chelating P,N‐hybrid ligand forms a ReI complex of the type [(N^N)Re(CO)3Br] through the coordination of nitrogen atom N2 to the metal centre rather than through the phosphorus donor. Both structural and spectroscopic data indicate substantial π‐accepting character of the triazaphosphole, which is again in contrast to that of the all‐nitrogen‐containing triazoles. The synthesis and photophysical properties of a new class of phosphorus‐containing extended π systems are described. 相似文献
5.
Copper Causes Regiospecific Formation of C4F8‐Containing Six‐Membered Rings and their Defluorination/Aromatization to C4F4‐Containing Rings in Triphenylene/1,4‐C4F8I2 Reactions
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Kerry C. Rippy Dr. Eric V. Bukovsky Dr. Tyler T. Clikeman Dr. Yu‐Sheng Chen Dr. Gao‐Lei Hou Dr. Xue‐Bin Wang Dr. Alexey A. Popov Dr. Olga V. Boltalina Prof. Steven H. Strauss 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(3):874-877
The presence of Cu in reactions of triphenylene (TRPH) and 1,4‐C4F8I2 at 360 °C led to regiospecific substitution of TRPH ortho C(β) atoms to form C4F8‐containing rings, completely suppressing substitution on C(α) atoms. In addition, Cu caused selective reductive‐defluorination/aromatization (RD/A) to form C4F4‐containing aromatic rings. Without Cu, the reactions of TRPH and 1,4‐C4F8I2 were not regiospecific and no RD/A was observed. These results, supported by DFT calculations, are the first examples of Cu‐promoted 1) regiospecific perfluoroannulation, 2) preparative C?F activation, and 3) RD/A. HPLC‐purified products were characterized by X‐ray diffraction, low‐temperature PES, and 1H/19F NMR. 相似文献
6.
Ruofei Cheng Jie Zhang Jiji Zhang Prof. Dr. Zaozao Qiu Prof. Dr. Zuowei Xie 《Angewandte Chemie (International ed. in English)》2016,55(5):1751-1754
The efficient o‐carboryne precursor 1‐Li‐2‐OTf‐o‐C2B10H10 reacts with lithium amides at room temperature to give a series of N‐carboranyl amines in moderate to high isolated yields. This reaction is compatible with a broad substrate scope from primary to secondary, alkyl to aryl amines. The reaction mechanism is also proposed on the basis of experimental results and DFT calculations. This represents the first general and efficient method for the synthesis of 1‐NR1R2‐o‐carboranes. 相似文献
7.
First Principles (DFT) Characterization of RhI/dppp‐Catalyzed CH Activation by Tandem 1,2‐Addition/1,4‐Rh Shift Reactions of Norbornene to Phenylboronic Acid
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Prof. Dr. Eric Assen B. Kantchev Surya R. Pangestu Dr. Feng Zhou Dr. Michael B. Sullivan Prof. Hai‐Bin Su 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(47):15625-15634
The C?H activation in the tandem, “merry‐go‐round”, [(dppp)Rh]‐catalyzed (dppp=1,3‐bis(diphenylphosphino)propane), four‐fold addition of norborene to PhB(OH)2 has been postulated to occur by a C(alkyl)?H oxidative addition to square‐pyramidal RhIII?H species, which in turn undergoes a C(aryl)?H reductive elimination. Our DFT calculations confirm the RhI/RhIII mechanism. At the IEFPCM(toluene, 373.15 K)/PBE0/DGDZVP level of theory, the oxidative addition barrier was calculated to be 12.9 kcal mol?1, and that of reductive elimination was 5.0 kcal mol?1. The observed selectivity of the reaction correlates well with the relative energy barriers of the cycle steps. The higher barrier (20.9 kcal mol?1) for norbornyl–Rh protonation ensures that the reaction is steered towards the 1,4‐shift (total barrier of 16.3 kcal mol?1), acting as an equilibration shuttle. The carborhodation (13.2 kcal mol?1) proceeds through a lower barrier than the protonation (16.7 kcal mol?1) of the rearranged aryl–Rh species in the absence of o‐ or m‐substituents, ensuring multiple carborhodations take place. However, for 2,5‐dimethylphenyl, which was used as a model substrate, the barrier for carborhodation is increased to 19.4 kcal mol?1, explaining the observed termination of the reaction at 1,2,3,4‐tetra(exo‐norborn‐2‐yl)benzene. Finally, calculations with (Z)‐2‐butene gave a carborhodation barrier of 20.2 kcal mol?1, suggesting that carborhodation of non‐strained, open‐chain substrates would be disfavored relative to protonation. 相似文献
8.
Discriminating Halogen‐Bonding from Other Noncovalent Interactions by a Combined NOE NMR/DFT Approach
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Dr. Gianluca Ciancaleoni Prof. Roberta Bertani Dr. Luca Rocchigiani Dr. Paolo Sgarbossa Dr. Cristiano Zuccaccia Prof. Alceo Macchioni 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(1):440-447
Herein a combined NOE NMR/DFT methodology to discriminate between adducts held together by halogen bonding (XB) and other noncovalent interactions (non‐XB, such as lone pair/π), based on the determination of the XB donors′ and acceptors′ relative orientation, is proposed. In particular, 19F,1H HOESY NMR spectroscopy experiments and DFT calculations on different XB donors, such as perfluorohexyl iodide ( I1 ), iodopentafluorobenzene ( I2 ) and bromopentafluorobenzene ( Br ), combined with different Lewis bases, such as 1,4‐diazabicyclo[2.2.2]octane ( DABCO ) and 2,4,6‐trimethylpyridine ( Me3Py ), were performed. The results clearly show that in the case DABCO / I1 the XB adduct is practically the only one present in solution, whereas for the other pairs a certain amount of non‐XB adduct is present. Combining DFT and HOESY results, the amount of non‐XB adducts can be roughly quantified under our experimental conditions as 4 % for DABCO / I2 , between 10 and 20 % for Me3Py / I1 and Me3Py / I2 , and 44 % for DABCO / Br. 相似文献
9.
From the N‐Heterocyclic Carbene‐Catalyzed Conjugate Addition of Alcohols to the Controlled Polymerization of (Meth)acrylates
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Winnie Nzahou Ottou Damien Bourichon Dr. Joan Vignolle Anne‐Laure Wirotius Dr. Fredéric Robert Prof. Yannick Landais Dr. Jean‐Marc Sotiropoulos Dr. Karinne Miqueu Prof. Daniel Taton 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(26):9447-9453
Among various N‐heterocyclic carbenes (NHCs) tested, only 1,3‐bis(tert‐butyl)imidazol‐2‐ylidene (NHCtBu) proved to selectively promote the catalytic conjugate addition of alcohols onto (meth)acrylate substrates. This rather rare example of NHC‐catalyzed 1,4‐addition of alcohols was investigated as a simple means to trigger the polymerization of both methyl methacrylate and methyl acrylate (MMA and MA, respectively). Well‐defined α‐alkoxy poly(methyl (meth)acrylate) (PM(M)A) chains, the molar masses of which could be controlled by the initial [(meth)acrylate]0/[ROH]0 molar ratio, were ultimately obtained in N,N‐dimethylformamide at 25 °C. A hydroxyl‐terminated poly(ethylene oxide) (PEO‐OH) macro‐initiator was also employed to directly access PEO‐b‐PMMA amphiphilic block copolymers. Investigations into the reaction mechanism by DFT calculations revealed the occurrence of two competitive concerted pathways, involving either the activation of the alcohol or that of the monomer by NHCtBu. 相似文献
10.
Faqian Liu Yanling Jin Baocheng Liu Rongxun Li Yueyi Deng Weihua Li Fangfang Jian 《中国化学》2012,30(5):1069-1074
A new candidate [Cu(PPh3)2Him]Br ( 1 , PPh3=triphenylphosphine, Him=1‐H‐imidazole) for nonlinear optical (NLO) materials has been synthesized and characterized crystallographically. The third‐order NLO optical properties were measured by the Z‐scan technique with an 8 ns pulsed laser at 532 nm. Compound 1 exhibits strong NLO absorptive abilities [α2=(61±5)×10?12] and effective self‐focusing performance [n2=(15±3)×10?18 m2·W?1] in 1.01×10?4 mol·dm?3 DMF solution. The compound also exhibits luminescence in DMF solution at room temperature and shows narrow emission with maximum at 382 nm. The electronic structure and photoluminescent process were investigated by means of TD‐DFT calculations. The results suggest that the contribution to the frontier orbitals from the Cu? Br δ bond plays a crucial role in its linear optical properties, and the origin of luminescence is attributable to the π??→n transitions. 相似文献
11.
Venkataraman Ganesh Dr. Devarajulu Sureshkumar Debasree Chanda Prof. Srinivasan Chandrasekaran 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(39):12498-12511
We present a detailed study of a [3+2+1] cascade cyclisation of vinylcyclopropanes (VCP) catalysed by a bromenium species (Brδ+? Xδ?) generated in situ, which results in the synthesis of chiral bicyclic amidines in a tandem one‐pot operation. The formation of amidines involves the ring‐opening of VCPs with Br? X, followed by a Ritter‐type reaction with chloramine‐T and a tandem cyclisation. The reaction has been further extended to vinylcyclobutane systems and involves a [4+2+1] cascade cyclisation with the same reagents. The versatility of the methodology has been demonstrated by careful choice of VCPs and VCBs to yield bicyclo[4.3.0]‐, ‐[4.3.1]‐ and ‐[4.4.0]amidines in enantiomerically pure form. On the basis of the experimental observations and DFT calculations, a reasonable mechanism has been put forth to account for the formation of the products and the observed stereoselectivity. We propose the existence of a π‐stabilised homoallylic carbocation at the cyclopropane carbon as the reason for high stereoselectivity. DFT studies at B3LYP/6‐311+G** and M06‐2X/6‐31+G* levels of theory in gas‐phase calculations suggest the ring‐opening of VCP is initiated at the π‐complex stage (between the double bond and Br? X). This can be clearly perceived from the solution‐phase (acetonitrile) calculations using the polarisable continuum model (PCM) solvation model, from which the extent of the ring opening of VCP was found to be noticeably high. Studies also show that the formation of zero‐bridge bicyclic amidines is favoured over other bridged bicyclic amidines. The energetics of competing reaction pathways is compared to explain the product selectivity. 相似文献
12.
Albert Paparo Cory D. Smith Cameron Jones 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(33):11581-11585
Additions of beryllium–halide bonds in the simple beryllium dihalide adducts, [BeX2(tmeda)] (X=Br or I, tmeda=N,N,N′,N′‐tetramethylethylenediamine), across the metal center of a neutral aluminum(I) heterocycle, [:Al(DipNacnac)] (DipNacnac=[(DipNCMe)2CH]?, Dip=2,6‐diisopropylphenyl), have yielded the first examples of compounds with beryllium–aluminum bonds, [(DipNacnac)(X)Al‐Be(X)(tmeda)]. For sake of comparison, isostructural Mg–Al and Zn–Al analogues of these complexes, viz. [(DipNacnac)(X)Al‐M(X)(tmeda)] (M=Mg or Zn, X=I or Br) have been prepared and structurally characterized. DFT calculations reveal all compounds to have high s‐character metal–metal bonds, the polarity of which is consistent with the electronegativities of the metals involved. Preliminary reactivity studies of [(DipNacnac)(Br)Al‐Be(Br)(tmeda)] are reported. 相似文献
13.
Dynamics of the NbCl5‐Catalyzed Cycloaddition of Propylene Oxide and CO2: Assessing the Dual Role of the Nucleophilic Co‐Catalysts
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Dr. Valerio D'Elia Dr. Amylia A. Ghani Dr. Antoine Monassier Dr. Julien Sofack‐Kreutzer Dr. Jeremie D. A. Pelletier Dr. Markus Drees Dr. Sai V. C. Vummaleti Dr. Albert Poater Prof. Dr. Luigi Cavallo Dr. Mirza Cokoja Prof. Dr. Jean‐Marie Basset Prof. Dr. Fritz. E. Kühn 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(37):11870-11882
A mechanistic study on the synthesis of propylene carbonate (PC) from CO2 and propylene oxide (PO) catalyzed by NbCl5 and organic nucleophiles such as 4‐dimethylaminopyridine (DMAP) or tetra‐n‐butylammonium bromide (NBu4Br) is reported. A combination of in situ spectroscopic techniques and kinetic studies has been used to provide detailed insight into the reaction mechanism, the formation of intermediates, and interactions between the reaction partners. The results of DFT calculations support the experimental observations and allow us to propose a mechanism for this reaction. 相似文献
14.
Pablo Ríos Dr. Josefina Díez Dr. Joaquín López‐Serrano Dr. Amor Rodríguez Dr. Salvador Conejero 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(47):16791-16795
The low‐electron‐count cationic platinum complex [Pt(ItBu’)(ItBu)][BArF], 1 , interacts with primary and secondary silanes to form the corresponding σ‐SiH complexes. According to DFT calculations, the most stable coordination mode is the uncommon η1‐SiH. The reaction of 1 with Et2SiH2 leads to the X‐ray structurally characterized 14‐electron PtII species [Pt(SiEt2H)(ItBu)2][BArF], 2 , which is stabilized by an agostic interaction. Complexes 1 , 2 , and the hydride [Pt(H)(ItBu)2][BArF], 3 , catalyze the hydrosilation of CO2, leading to the exclusive formation of the corresponding silyl formates at room temperature. 相似文献
15.
Mateusz Piontek Bernd Morgenstern Nils Steinbrück Bastian Oberhausen Guido Kickelbick Kaspar Hegetschweiler 《Acta Crystallographica. Section C, Structural Chemistry》2019,75(6):678-685
Liu et al. [Chin. J. Struct. Chem. (1996). 15 , 371–373] reported the structure of 6‐hydroxy‐1,4‐diazepane di(hydrogen bromide), C5H12N2O·2HBr, which was interpreted in terms of neutral diazepane and HBr molecules. We found, however, ample evidence that the formation of an organic salt, consisting of a diammonium cation and two bromide anions, is more plausible. This interpretation is also in agreement with thermogravimetric analysis and with the observed solution behaviour. The crystal structure of 6‐hydroxy‐1,4‐diazepane‐1,4‐diium dibromide, C5H14N2O2+·2Br?, measured at 142 K, crystallized in the orthorhombic space group P212121. The structure displays O—H…Br and N—H…Br hydrogen bonding. Contact distances are given. A search in the Cambridge Structural Database for the singly‐bonded H—Br moiety revealed a total of 69 structures. The question, whether these structures really include HBr as neutral molecules or rather Br? anions and a protonated substrate such as an amine, is addressed. 相似文献
16.
Lucia Ambrosio M. Carla Aragoni Dr. Massimiliano Arca Dr. Francesco A. Devillanova Prof. Michael B. Hursthouse Prof. Dr. Susanne L. Huth Dr. Francesco Isaia Prof. Vito Lippolis Prof. Dr. Annalisa Mancini Dr. Anna Pintus Dr. 《化学:亚洲杂志》2010,5(6):1395-1406
The tetrabutylammonium (TBA+) salts of square‐planar monoanionic gold complexes of the unsymmetrically substituted Ar,H‐edt2? 1,2‐dithiolene ligands (Ar,H‐edt2?=arylethylene‐1,2‐dithiolato; Ar=phenyl ( 1 ?), 2‐naphthyl ( 2 ?), and 1‐pyrenyl ( 3 ?)) were synthesized and characterized by spectroscopic and electrochemical methods and the corresponding neutral species ( 1 , 2 , and 3 , respectively) were obtained in CH2Cl2 solution at room temperature by diiodine oxidation. The single‐crystal X‐ray diffraction structural data collected for (TBA+)( 2 ?), supported by DFT theoretical calculations, are consistent with the ene‐1,2‐dithiolate form of the ligand and the AuIII oxidation state. All complexes feature intense near‐IR absorptions (at about 1.5 μm) in their neutral states and Vis‐emitting properties in the 400–550 nm range, the energy of which is controlled by the charge of the complex in the case of the 3 ?/ 3 couple. The spectroscopic and electrochemical features of 1 x? and 2 x? (x=0, 1), both in their cis and trans conformations, were investigated by means of DFT and time‐dependent (TD) DFT calculations. 相似文献
17.
Divergent Pathways and Competitive Mechanisms of Metathesis Reactions between 3‐Arylprop‐2‐ynyl Esters and Aldehydes: An Experimental and Theoretical Study
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Dr. Cristina Trujillo Dr. Goar Sánchez‐Sanz Ieva Karpavičienė Dr. Ullrich Jahn Dr. Inga Čikotienė Dr. Lubomír Rulíšek 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(33):10360-10370
Mechanistic studies of the reaction between 3‐arylprop‐2‐ynyl esters and aldehydes catalyzed by BF3 ? Et2O were performed by isotopic labeling experiments and quantum chemical calculations. The reactions are shown to proceed by either a classical alkyne–carbonyl metathesis route or an unprecedented addition–rearrangement cascade. Depending on the structure of the starting materials and the reaction conditions, the products of these reactions can be Morita–Baylis–Hillman (MBH) adducts that are unavailable by traditional MBH reactions or E‐ and Z‐α,β‐unsaturated ketones. 18O‐Labeling studies suggested the existence of two different reaction pathways to the products. These pathways were further examined by quantum chemical calculations that employed the DFT(wB97XD)/6‐311+G(2d,p) method, together with the conductor‐like screening model for realistic solvation (COSMO‐RS). By using the wB97XD functional, the accuracy of the computed data is estimated to be 1–2 kcal mol?1, shown by the careful benchmarking of various DFT functionals against coupled cluster calculations at the CCSD(T)/aug‐cc‐pVTZ level of theory. Indeed, most of the experimental data were reproduced and explained by theory and it was convincingly shown that the branching point between the two distinct mechanisms is the formation of the first intermediate on the reaction pathway: either the four‐membered oxete or the six‐membered zwitterion. The deep mechanistic understanding of these reactions opens new synthetic avenues to chemically and biologically important α,β‐unsaturated ketones. 相似文献
18.
Investigation of Mizoroki‐Heck coupling polymerization as a catalyst‐transfer condensation polymerization for synthesis of poly(p‐phenylenevinylene)
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Masataka Nojima Ryosuke Saito Yoshihiro Ohta Tsutomu Yokozawa 《Journal of polymer science. Part A, Polymer chemistry》2015,53(4):543-551
Mizoroki‐Heck coupling polymerization of 1,4‐bis[(2‐ethylhexyl)oxy]‐2‐iodo‐5‐vinylbenzene ( 1 ) and its bromo counterpart 2 with a Pd initiator for the synthesis of poly(phenylenevinylene) (PPV) was investigated to see whether the polymerization proceeds in a chain‐growth polymerization manner. The polymerization of 1 with tBu3PPd(Tolyl)Br ( 10 ) proceeded even at room temperature when 5.5 equiv of Cy2NMe (Cy = cyclohexyl) was used as a base, but the molecular weight distribution of PPV was broad. The polymerization of 2 hardly proceeded at room temperature under the same conditions. In the polymerization of 1 , PPV with H at one end and I at the other was formed until the middle stage, and the polymer end groups were converted into tolyl and H in the final stage. The number‐average molecular weight (Mn) did not increase until about 90% monomer conversion and then sharply increased after that, indicating conventional step‐growth polymerization. The occurrence of step‐growth polymerization, not catalyst‐transfer chain‐growth polymerization, may be interpreted in terms of low coordination ability of H‐Pd(II)‐X(tBu3P) (X = Br or I), formed in the catalytic cycle of the Mizoroki‐Heck coupling reaction, to π‐electrons of the PPV backbone; reductive elimination of H‐X from this Pd species with base would take place after diffusion into the reaction mixture. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 543–551 相似文献
19.
Matthias Prall Alexander Wittkopp Andrey A. Fokin Peter R. Schreiner 《Journal of computational chemistry》2001,22(13):1605-1614
The effects of several substituents (? BH2, ? BF2, ? AlH2, ? CH3, ? C6H5, ? CN, ? COCH3, ? CF3, ? SiH3, ? NH2, ? NH3+, ? NO2, ? PH2, ? OH, ? OH2+, ? SH, ? F, ? Cl, ? Br) on the Bergman cyclization of (Z)‐1,5‐hexadiyne‐3‐ene (enediyne, 3 ) were investigated at the Becke–Lee–Yang–Parr (BLYP) density functional (DFT) level employing a 6‐31G* basis set. Some of the substituents (? NH3+, ? NO2, ? OH, ? OH2+, ? F, ? Cl, ? Br) are able to lower the barrier (up to a minimum of 16.9 kcal mol?1 for difluoro‐enediyne 7rr ) and the reaction enthalpy (the cyclization is predicted to be exergonic for ? OH2+ and ? F) compared to the parent system giving rise to substituted 1,4‐dehydrobenzenes at physiological temperatures. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 1605–1614, 2001 相似文献
20.
Nell S. Townsend Adrian B. Chaplin Dr. M. Abu Naser Dr. Amber L. Thompson Dr. Nicholas H. Rees Dr. Stuart A. Macgregor Prof. Andrew S. Weller Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(28):8376-8389
Oxidative addition of aryl bromides to 12‐electron [Rh(PiBu3)2][BArF4] (ArF=3,5‐(CF3)2C6H3) forms a variety of products. With p‐tolyl bromides, RhIII dimeric complexes result [Rh(PiBu3)2(o/p‐MeC6H4)(μ‐Br)]2[BArF4]2. Similarly, reaction with p‐ClC6H4Br gives [Rh(PiBu3)2(p‐ClC6H4)(μ‐Br)]2[BArF4]2. In contrast, the use of o‐BrC6H4Me leads to a product in which toluene has been eliminated and an isobutyl phosphine has undergone C? H activation: [Rh{PiBu2(CH2CHCH3C H2)}(PiBu3)(μ‐Br)]2[BArF4]2. Trapping experiments with ortho‐bromo anisole or ortho‐bromo thioanisole indicate that a possible intermediate for this process is a low‐coordinate RhIII complex that then undergoes C? H activation. The anisole and thioanisole complexes have been isolated and their structures show OMe or SMe interactions with the metal centre alongside supporting agostic interactions, [Rh(PiBu3)2(C6H4O Me)Br][BArF4] (the solid‐state structure of the 5‐methyl substituted analogue is reported) and [Rh(PiBu3)2(C6H4S Me)Br][BArF4]. The anisole‐derived complex proceeds to give [Rh{PiBu2(CH2CHCH3C H2)}(PiBu3)(μ‐Br)]2[BArF4]2, whereas the thioanisole complex is unreactive. The isolation of [Rh(PiBu3)2(C6H4O Me)Br][BArF4] and its onward reactivity to give the products of C? H activation and aryl elimination suggest that it is implicated on the pathway of a σ‐bond metathesis reaction, a hypothesis strengthened by DFT calculations. Calculations also suggest that C? H bond cleavage through phosphine‐assisted deprotonation of a non‐agostic bond is also competitive, although the subsequent protonation of the aryl ligand is too high in energy to account for product formation. C? H activation through oxidative addition is also ruled out on the basis of these calculations. These new complexes have been characterised by solution NMR/ESIMS techniques and in the solid‐state by X‐ray crystallography. 相似文献