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971.
Sañudo EC Cauchy T Ruiz E Laye RH Roubeau O Teat SJ Aromí G 《Inorganic chemistry》2007,46(22):9045-9047
With the help of a bis(beta-diketonate) ligand, a family of robust molecules is formed, all consisting of two [Mn(III)4] subunits that interact slightly magnetically with each other, through two bridging pyrazine ligands. 相似文献
972.
Lyudmila V. Parfenova Rushana F. Vil’danova Svetlana V. Pechatkina Leonard M. Khalilov Usein M. Dzhemilev 《Journal of organometallic chemistry》2007,692(16):3424-3429
New bimetallic complex [Cp2ZrH2 · ClAlEt2]2 (1) was synthesized, and its reactivity in hydrometallation reaction with the following alkenes was studied: hept-1-ene, okt-1-ene, α-methylstyrene, (1S)-β-pinene, (+)-camphene. Complex 1 shows the highest reactivity among the other known Al,Zr-bimetallic complexes: [Cp2ZrH2 · ClAlBui2]2 (2), [Cp2ZrH2 · AlEt3]2 (3), [Cp2ZrH2 · AlBui3]2 (4) and [Cp2ZrH2 · HAlBui2] (5) as well as organoaluminium compounds (OAC): iBu2AlH, iBu3Al and iBu2AlCl in presence of Zr catalysts. Chlorine containing complexes 1 and 2 appear to be more effective in alkene hydrometallation, and relative hydrometallation rates are (1S)-β-pinene ? (+)-camphene < α-methylstyrene < oct-1-ene < hept-1-ene. Hydrometallation of (1S)-β-pinene and its subsequent oxidation with I2 run with high diastereoselectivity and yield trans-myrtanol. However, the diastereoselectivity of (+)-camphene hydrometallation is less than that for (1S)-β-pinene, and the reaction gives predominately endo-camphanol. 相似文献
973.
Forbes MW Bush MF Polfer NC Oomens J Dunbar RC Williams ER Jockusch RA 《The journal of physical chemistry. A》2007,111(46):11759-11770
The structures of cationized arginine complexes [Arg + M]+, (M = H, Li, Na, K, Rb, Cs, and Ag) and protonated arginine methyl ester [ArgOMe + H]+ have been investigated in the gas phase using calculations and infrared multiple-photon dissociation spectroscopy between 800 and 1900 cm-1 in a Fourier transform ion cyclotron resonance mass spectrometer. The structure of arginine in these complexes depends on the identity of the cation, adopting either a zwitterionic form (in salt-bridge complexes) or a non-zwitterionic form (in charge-solvated complexes). A diagnostic band above 1700 cm-1, assigned to the carbonyl stretch, is observed for [ArgOMe + H]+ and [Arg + M]+, (M = H, Li, and Ag), clearly indicating that Arg in these complexes is non-zwitterionic. In contrast, for the larger alkali-metal cations (K+, Rb+, and Cs+) the measured IR-action spectra indicate that arginine is a zwitterion in these complexes. The measured spectrum for [Arg + Na]+ indicates that it exists predominantly as a salt bridge with zwitterionic Arg; however, a small contribution from a second conformer (most likely a charge-solvated conformer) is also observed. While the silver cation lies between Li+ and Na+ in metal-ligand bond distance, it binds as strongly or even more strongly to oxygen-containing and nitrogen-containing ligands than the smaller Li+. The measured IR-action spectrum of [Arg + Ag]+ clearly indicates only the existence of non-zwitterionic Arg, demonstrating the importance of binding energy in conformational selection. The conformational landscapes of the Arg-cation species have been extensively investigated using a combination of conformational searching and electronic structure theory calculations [MP2/6-311++G(2d,2p)//B3LYP/6-31+G(d,p)]. Computed conformations indicate that Ag+ is di-coordinated to Arg, with the Ag+ chelated by both the N-terminal nitrogen and Neta of the side chain but lacks the strong M+-carbonyl oxygen interaction that is present in the tri-coordinate Li+ and Na+ charge-solvation complexes. Experiment and theory show good agreement; for each ion species investigated, the global-minimum conformer provides a very good match to the measured IR-action spectrum. 相似文献
974.
Ismail H Goldsmith CF Abel PR Howe PT Fahr A Halpern JB Jusinski LE Georgievskii Y Taatjes CA Green WH 《The journal of physical chemistry. A》2007,111(29):6843-6851
This work reports measurements of absolute rate coefficients and Rice-Ramsperger-Kassel-Marcus (RRKM) master equation simulations of the C2H3+C2H4 reaction. Direct kinetic studies were performed over a temperature range of 300-700 K and pressures of 20 and 133 mbar. Vinyl radicals (H2C=CH) were generated by laser photolysis of vinyl iodide (C2H3I) at 266 nm, and time-resolved absorption spectroscopy was used to probe vinyl radicals through absorption at 423.2 nm. Measurements at 20 mbar are in good agreement with previous determinations at higher temperature. A weighted three-parameter Arrhenius fit to the experimental rate constant at 133 mbar, with the temperature exponent fixed, gives k=(7+/-1)x10(-14) cm3 molecule(-1) s(-1) (T/298 K)2 exp[-(1430+/-70) K/T]. RRKM master equation simulations, based on G3 calculations of stationary points on the C4H7 potential energy surface, were carried out to predict rate coefficients and product branching fractions. The predicted branching to 1-methylallyl product is relatively small under the conditions of the present experiments but increases as the pressure is lowered. Analysis of end products of 248 nm photolysis of vinyl iodide/ethylene mixtures at total pressures between 27 and 933 mbar provides no direct evidence for participation of 1-methylallyl. 相似文献
975.
Ayan Dasgupta Emma Richards Rebecca L. Melen 《Angewandte Chemie (International ed. in English)》2021,60(1):53-65
Progress in frustrated Lewis pair (FLP) chemistry has revealed the importance of the main group elements in catalysis, opening new avenues in synthetic chemistry. Recently, new reactivities of frustrated Lewis pairs have been uncovered that disclose that certain combinations of Lewis acids and bases undergo single‐electron transfer (SET) processes. Here an electron can be transferred from the Lewis basic donor to a Lewis acidic acceptor to generate a reactive frustrated radical pair (FRP). This minireview aims to showcase the recent advancements in this emerging field covering the synthesis and reactivities of frustrated radical pairs, with extensive highlights of the results from Electron Paramagnetic Resonance (EPR) spectroscopy to explain the nature and stability of the different radical species observed. 相似文献
976.
977.
Gerrit Schaper Dr. Marco Wenzel Dr. Felix Hennersdorf Prof. Dr. Leonard F. Lindoy Prof. Dr. Jan J. Weigand 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(33):8484-8491
The reaction of UO2(OAc)2 ⋅ 2H2O with the biologically inspired ligand 2-salicylidene glucosamine (H2 L1 ) results in the formation of the anionic trinuclear uranyl complex [(UO2)3(μ3-O)( L1 )3]2− ( 1 2−), which was isolated in good yield as its Cs-salt, [Cs]2 1 . Recrystallization of [Cs]2 1 in the presence of 18-crown-6 led to formation of a neutral ion pair of type [M(18-crown-6)]2 1 , which was also obtained for the alkali metal ions Rb+ and K+ (M=Cs, Rb, K). The related ligand, 2-(2-hydroxy-1-naphthylidene) glucosamine (H2 L2 ) in a similar procedure with Cs+ gave the corresponding complex [Cs(18-crown-6)]2[(UO2)3(μ3-O)( L2 )3 ([Cs(18-crown-6)]2 2 ). From X-ray investigations, the [(UO2)3O( Ln )3]2− anion (n=1, 2) in each complex is a discrete trinuclear uranyl species that coordinates to the alkali metal ion via three uranyl oxygen atoms. The coordination behavior of H2 L1 and H2 L2 towards UO22+ was investigated by NMR, UV/Vis spectroscopy and mass spectrometry, revealing the in situ formation of the 1 2− and 2 2−dianions in solution. 相似文献
978.
Dr. Aigui Zhang Dr. Simone Budow-Busse Dr. Peter Leonard Prof. Dr. Frank Seela 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(41):10574-10577
Dodecamer duplex DNA containing anomeric (α/β-d ) and enantiomeric (β-l /β-d ) 2’-deoxycytidine mismatches was studied with respect to base pair stability in the absence and presence of silver ions. Stable duplexes with silver-mediated cytosine–cytosine pairs were formed by all anomeric and enantiomeric combinations. Stability changes were observed depending on the composition of the mismatches. Most strikingly, the new silver-mediated base pair of anomeric α-d -dC with enantiomeric β-l -dC is superior to the well-noted β-d /β-d -dC pair in terms of stability. CD spectra were used to follow global helical changes of DNA structure. 相似文献
979.
Yingying Chai Dr. Dasharath Kondhare Dr. Aigui Zhang Dr. Peter Leonard Prof. Dr. Frank Seela 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(6):2093-2103
Stabilization of DNA is beneficial for many applications in the fields of DNA therapeutics, diagnostics, and materials science. Now, this phenomenon is studied on heterochiral DNA, an autonomous DNA recognition system with complementary strands in α-D and β-D configuration showing parallel strand orientation. The 12-mer heterochiral duplexes were constructed from anomeric (α/β-D) oligonucleotide single-strands. Purine-2,6-diamine and 8-aza-7-deaza-7-bromopurine-2,6-diamine 2′-deoxyribonucleosides having the capability to form tridentate base pairs with dT were used to strengthen the stability of the dA–dT base pair. Tm data and thermodynamic values obtained from UV melting profiles indicated that the 8-aza-7-deaza 2′-deoxyribonucleoside decorated with a bromo substituent is so far the most efficient stabilizer for heterochiral DNA. Compared with that, the stabilizing effect of the purine-2,6-diamine 2′-deoxyribonucleoside is low. Global changes of helix structures were identified by circular dichroism (CD) spectra during melting. 相似文献
980.
Kyle W. Knouse Laura E. Ator Lauren E. Beausoleil Zachary J. Hauseman Rebecca L. Casaubon Gregory R. Ott 《Tetrahedron letters》2017,58(3):202-205
Improved and expanded one-pot, two-component syntheses of bicyclic heterocycles containing a 3-N-acyl-3-amino-1,2-pyrazole motif from N′-hydroxy-carboxyamidines and acylbenzotriazoles have been developed. Importantly, this sequence obviates the need for hydrazine or N-aminating reagents to synthesize the key nitrogen–nitrogen (N–N) bond of these heterocycles, which is formed via Boulton-Katritzky rearrangement. A diverse array of pharmaceutically relevant N–N containing heterocycles has been prepared with this methodology using readily available reagents without the need for special equipment or conditions. 相似文献