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151.
Haihua Wang Yonghao Ni M. Sarwar Jahan Zehua Liu Thioni Schafer 《Journal of Thermal Analysis and Calorimetry》2011,103(1):293-302
The thermo-oxidative stability of acetic acid lignin-containing polyurethane (LPU) that contains cross-linking agents, such
as 1-aminopropyltriethoxy-silane (APTS) and/or trimethylolpropane (TMP) was investigated based on the thermogravimetric analysis
(TGA) method, their kinetic parameters in the thermo-oxidative process was determined. FT-IR certified the occurrence of interaction
between lignin and polyurethane (PU). It was found that continuous membrane can be formed when lignin concentration was 43.3%,
but rupture took place when it increased to 50%. When the degradation was performed in nitrogen, TG and dynamic differential
thermogravimetry (DTG) results demonstrated that the PU underwent three stages of degradation while the LPU involved one main
degradation stage with a shoulder, and the degradation stability increased with the increase in the lignin concentration and
PEG length. It was also found that the addition of a cross-linking agent is beneficial to the improvement of thermal stability
and, in particular, APTS gave the best thermal stability for the LPU produced, among the cross-linking agents tested. Furthermore,
LPU exhibited multistage degradation process in air and displayed higher thermo-oxidative stability than PU. At the same time,
the kinetic study showed that LPU modified with APTS exhibited higher activation energy than LPU modified with TMP. And the
maximum activation energy was found for the sample modified with the simultaneous addition of APTS and TMP. 相似文献
152.
Four‐Membered Heterometallacyclic d0 and d1 Complexes of Group 4 Metallocenes with Amidato Ligands 下载免费PDF全文
Dr. Martin Haehnel Jacqueline B. Priebe Jacky C.‐H. Yim Dr. Anke Spannenberg Prof. Dr. Angelika Brückner Prof. Dr. Laurel L. Schafer Prof. Dr. Uwe Rosenthal 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(25):7752-7758
A study of the coordination chemistry of different amidato ligands [(R)N?C(Ph)O] (R=Ph, 2,6‐diisopropylphenyl (Dipp)) at Group 4 metallocenes is presented. The heterometallacyclic complexes [Cp2M(Cl){κ2‐N,O‐(R)N?C(Ph)O}] M=Zr, R=Dipp ( 1 a ), Ph ( 1 b ); M=Hf, R=Ph ( 2 )) were synthesized by reaction of [Cp2MCl2] with the corresponding deprotonated amides. Complex 1 a was also prepared by direct deprotonation of the amide with Schwartz reagent [Cp2Zr(H)Cl]. Salt metathesis reaction of [Cp2Zr(H)Cl] with deprotonated amide [(Dipp)N?C(Ph)O] gave the zirconocene hydrido complex [Cp2M(H){κ2‐N,O‐(Dipp)N?C(Ph)O}] ( 3 ). Reaction of 1 a with Mg did not result in the desired Zr(III) complex but in formation of Mg complex [(py)3Mg(Cl) {κ2‐N,O‐(Dipp)N?C(Ph)O}] ( 4 ; py=pyridine). The paramagnetic complexes [Cp′2Ti{κ2‐N,O‐(R)N?C(Ph)O}] (Cp′=Cp, R=Ph ( 7 a ); Cp′=Cp, R=Dipp ( 7 b ); Cp′=Cp*, R=Ph ( 8 )) were prepared by the reaction of the known titanocene alkyne complexes [Cp2′Ti(η2‐Me3SiC2SiMe3)] (Cp′=Cp ( 5 ), Cp′=Cp* ( 6 )) with the corresponding amides. Complexes 1 a , 2 , 3 , 4 , 7 a , 7 b , and 8 were characterized by X‐ray crystallography. The structure and bonding of complexes 7 a and 8 were also characterized by EPR spectroscopy. 相似文献
153.
Horrillo-Martinez P Patrick BO Schafer LL Fryzuk MD 《Dalton transactions (Cambridge, England : 2003)》2012,41(5):1609-1616
A series of mixed Cp* amidate tantalum complexes Cp*Ta(RNC(O)R')X(3) (where R = Me(2)C(6)H(3), (i)Pr, R' = (t)Bu, Ph, X = Cl, Me) have been prepared via salt metathesis and their fundamental reactivities under reducing conditions have been explored. Reaction of the tantalum chloro precursors with potassium graphite under N(2) or Ar leads to the stereoselective formation of the terminal tantalum oxo species, Cp*Ta=O(η(2)-RN=CR')Cl. This represents the formal extrusion of oxygen from the amidate ligand to the reduced tantalum center and is accompanied by the formation of the iminoacyl fragment bound to Ta(v). Amidate dinitrogen complexes, [Cp*TaCl(RNC(O)(t)Bu)](2)(μ-N(2)) (where R = Me(2)C(6)H(3), (i)Pr) were synthesized via salt metathesis from the known [Cp*TaCl(2)](2)(μ-N(2)) precursor, establishing that amidate ligands can support dinitrogen complexes, but not the reduction process often necessary for their synthesis. 相似文献
154.
Duane E. Weisshaar Gary W. Earl Eric M. Villa Jessica L. Zierke Christopher J. Fry Kara L. Becvar Shik Ki Li Matthew C. Schafer 《国际化学动力学杂志》2010,42(4):221-225
Quaternary ammonium compounds are produced worldwide in hundreds of millions of pound volume annually for a plethora of end‐uses from fabric‐care formulations to asphalt emulsifiers, typically from nongreen alkylating reagents. The kinetics of a reaction employing dimethyl carbonate (DMC) as a green alkylating agent was investigated using three trialkylamines (tributylamine, trihexylamine, and trioctylamine) at several temperatures. Arrhenius and Eyring analysis of the data showed that values of Ea (79 kJ/mol), ΔH? (75 kJ/mol), and ΔS? (220 J/(mol K)) were the same for all three amine reactants, consistent with a report that Ea is independent of alkyl chain length when the chain length is greater than three carbons. Although rates are significantly slower with DMC than with other alkylating reagents, the resulting methyl carbonate anion has advantages for clean anion metathesis, which is important for some applications, especially those involving ionic liquids. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 221–225, 2010 相似文献
155.
Alma R. Morales Dr. Katherine J. Schafer‐Hales Dr. Ciceron O. Yanez Mykhailo V. Bondar Dr. Olga V. Przhonska Dr. Adam I. Marcus Prof. Kevin D. Belfield Prof. 《Chemphyschem》2009,10(12):2073-2081
The steady‐state photophysical, NMR, and two‐photon absorption (2PA) properties of a new fluorene derivative ( 1 ) containing the 2‐(2′‐hydroxyphenyl)benzothiazole (HBT) terminal construct is investigated for use as a fluorescence probe in bioimaging. A comprehensive analysis of the linear spectral properties reveals inter‐ and intramolecular hydrogen bonding and excited state intramolecular proton transfer (ESIPT) processes in the HBT substituent. A specific electronic model with a double minimum potential energy surface is consistent with the observed spectral properties. The 2PA spectra are obtained using a standard two‐photon induced fluorescence method with a femtosecond kHz laser system, affording a maximum 2PA cross section of ~600 GM, a sufficiently high value for two‐photon fluorescence imaging. No dependence of two‐photon absorption efficiency on solvent properties and hydrogen bonding in the HBT substituent is observed. The potential use of this fluorenyl probe in bioimaging is demonstrated via one‐ and two‐photon fluorescence imaging of COS‐7 cells. 相似文献
156.
J.A. Schafer 《Commentarii Mathematici Helvetici》1999,74(2):173-178
The following question, which is directly related to the Whitehead problem of subcomplexes of acyclic 2-complexes, is studied:
If is a class of groups, X is a 2-dimensional CW-complex and X' is an acyclic, infinite cyclic cover of X with in , must X' be contractible? A positive answer is given if X is finite and is the class of amenable groups.
Received: April 24, 1995. 相似文献
157.
Weiying He D. Dawson Beattie Hao Zhou Eric G. Bowes Laurel L. Schafer Jennifer A. Love Pierre Kennepohl 《Chemical science》2021,12(46):15298
Agostic interactions are examples of σ-type interactions, typically resulting from interactions between C–H σ-bonds with empty transition metal d orbitals. Such interactions often reflect the first step in transition metal-catalysed C–H activation processes and thus are of critical importance in understanding and controlling σ bond activation chemistries. Herein, we report on the unusual electronic structure of linear electron-rich d9 Ni(i) complexes with symmetric bis(C–H) agostic interactions. A combination of Ni K edge and L edge XAS with supporting TD-DFT/DFT calculations reveals an unconventional covalent agostic interaction with limited contributions from the valence Ni 3d orbitals. The agostic interaction is driven via the empty Ni 4p orbitals. The surprisingly strong Ni 4p-derived agostic interaction is dominated by σ contributions with minor π contributions. The resulting ligand–metal donation occurs directly along the C–Ni bond axis, reflecting a novel mode of bis-agostic bonding.Symmetric Ni(i) agostic complexes reveal an unusual mode of bonding that is dominated by direct carbon-to-metal charge transfer. 相似文献