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151.
Wolfgang A. Herrmann Cornelia Weber Manfred L. Ziegler Orhan Serhadli 《Journal of organometallic chemistry》1985,297(2):245-254
The diazoolefines of composition N2CCR2 (R/R = CH3/CH3 and(-CH2-)5) are suitable precursors of the corresponding vinylidene ligands CCR2. Thus, treatment of the RhRh complex [(η5-C5Me5)Rh(μ-CO)]2 (1) with the N-nitrosourethanes 2a and 2b, resp., in the presence of lithium t-butoxide yields the otherwise inaccessible μ-vinylidene complexes (μ-CCR2)[(η5-C5Me5)Rh(CO)]2 (R = CH3 (3a), R,R = (-CH2-)5 (3b)). The analogous cobalt compound (μ-CCMe2)[(η5-C5Me5)Co(CO)]2 (5a) is obtained similarly. This procedure extends the well-documented diazoalkane method for the synthesis of μ-alkylidene complexes to the less stable diazoalkenes. A single-crystal X-ray diffraction study of the dimethylvinylidene derivative 3a shows the CMe2 ligand to adopt an almost symmetrically metal-bridging position (d(RhC) 197.8(1) and 204.3(1) pm), with a rhodium-rhodium single bond completing a three-membered Rh2C-metallacycle (d(RhRh) 268.4(0) pm) analogous with cyclopropane. 相似文献
152.
Frank Sobott Andreas Wattenberg Wolfgang Kleinekofort Anja Pfenninger Bernhard Brutschy 《Analytical and bioanalytical chemistry》1998,360(7-8):745-749
A recently developed soft desorption method for mass spectrometry is presented, which is called Laser Induced Liquid Beam
Ionization/Desorption (LILBID). Analyte ions are desorbed from a thin jet of analyte solution directly into vacuum by means
of an IR laser pulse, which has been tuned to a vibrational resonance of the solvent. A comparative experiment with ammonium
chloride and aniline hydrochloride shows that ion formation via proton transfer takes place in the solution. Thermally unstable
compounds, as well as supra- and biomolecular complexes, can be detected intact and mass analyzed in a reflectron time-of-flight
(Re-TOF) mass spectrometer. During the desorption process, noncovalent interactions and some solvation characteristics are
preserved. Three examples for the capacity of LILBID are given in this short overview: (a) ion-solvent interactions with the formation of a clathrate structure Cs+(H2O)20, (b) host-guest interactions with the K+ selectivity of valinomycin, and (c) noncovalent interactions with the dimerization of gramicidin.
Received: 29 July 1997 / Revised: 4 September 1997 / Accepted: 12 September 1997 相似文献
153.
Butadienyloxirane-Dihydrooxepine Isomerisation. Ring Expansion Reactions of Sterically Fixed and Benzoannelated Epoxyhexadienes by 1,7-Electrocyclisation of Conjugated Carbonyl Ylides Thermal ring cleavage of specifically substituted oxiranes results in the formation of conjugated carbonyl ylide intermediates which react by 1,5- and/or 1,7-electrocyclisation to give ring-expanded products. While the spirooxiranes 5t, 6t , and 12t are transformed, as expected, only into 2,3-dihydrofurans ( 21, 22, 50 ), the geometrically fixed compounds give rise to the formation of seven-membered ring isomers either partially ( 6c ), or predominantly ( 5c ), or exclusively ( 7 – 11, 12c ). 1,7-Dipolar cyclisations also take place with participation of one or even two aromatic double bonds ( 7 → 52, 8 → 53, 9 → 54, 12c → 57 , and 10 → 55, 11 → 56 , resp.) affording mono- and dibenzo-dihydrooxepines, respectively. The rearrangements of 5c to 27 and 6c to 28 show for the first time that the 8π-ring closure of 2-oxaheptatrienyl dipoles proceeds in the theoretically predicted conrotatory manner. The exclusive, i.e. periselective formation of dihydrooxepines during the thermolysis of compounds 7 – 11, 12c is explained by assuming a helical geometry of the dipolar intermediates in which the stereoelectronic situation is specially suitable for the – entropically less advantageous – 1,7-cyclisation process. 相似文献
154.
The photoaddition 6 → 7 , followed by a reductive cleavage of the →-chlorocyclobutylketone 7 , gave the stereochemically pure spiro [4,5]decane 8 . 相似文献
155.
Zellner M Winkler W Hayden H Diestinger M Eliasen M Gesslbauer B Miller I Chang M Kungl A Roth E Oehler R 《Electrophoresis》2005,26(12):2481-2489
For the preparation of proteins for proteome analysis, precipitation is frequently used to concentrate proteins and to remove interfering compounds. Various methods for protein precipitation are applied, which rely on different chemical principles. This study compares the changes in the protein composition of human blood platelet extracts after precipitation with ethanol (EtOH) or trichloroacetic acid (TCA). Both methods yielded the same amount of proteins from the platelet preparations. However, the EtOH-precipitated samples had to be dialyzed because of the considerable salt content. To characterize single platelet proteins, samples were analyzed by two-dimensional fluorescence differential gel electrophoresis. More than 90% of all the spots were equally present in the EtOH- and TCA-precipitated samples. However, both precipitation methods showed a smaller correlation with nonprecipitated samples (EtOH 74.9%, TCA 79.2%). Several proteins were either reduced or relatively enriched in the precipitated samples. The proteins varied randomly in molecular weight and isoelectric point. This study shows that protein precipitation leads to specific changes in the protein composition of proteomics samples. This depends more on the specific structure of the protein than on the precipitating agent used in the experiment. 相似文献
156.
The synthesis, IR, 1H NMR and UV spectra of optically active square pyramidal cyclopentadienyldicarbonyl-molybdenum and -tungsten complexes with Schiff bases, derived from methyl-substituted pyridine carbaldehyde(2) and S-(—)-α-methylbenzylamine, are described. The epimerisation of these complexes, measured polarimetrically at 75–97°C in DMF, follows a 1st order rate law and represents a regular pentatopal skeletal rearrangement. The inductive effect of a methyl group in the para position of a pyridine ring leads to a retardation of the epimerisation compared to unsubstituted complexes. The rate constants decrease even more if an ortho methyl group is introduced into the pyridine system, since additional steric effects are introduced. If the metal complex contains a 4,6-dimethyl-substituted Schiff base as a chelating ligand, the contributions of a 4- and a 6-methyl group are additive. A benzene ring fused to the 5,6-positions of the pyridine system also leads to stabilisation of the configuration. 相似文献
157.
The thermal ring expansion reaction of (Z)-styryloxiranes (-) involves phenylring participation leading to 2,7-dihydro-3,4-benzoxepins (-). 相似文献
158.
Helmut Quast Josef Christ Yvonne Görlach Wolfgang von der Saal 《Tetrahedron letters》1982,23(36):3653-3656
The 2,6-dicyano-1,5-dimethylsemibullvalene (2d) synthesized via the bicyclo[3.3.0]octanedione 7 exists as a classical ground state which is lower in energy by less than 5 kcal/mole than the homoaromatic transition of the Cope rearrangement of 2d. 相似文献
159.
Benchmarking of ruthenium initiators for the ROMP of a norbornenedicarboxylic acid ester 总被引:1,自引:0,他引:1
Sandra Demel Wolfgang Schoefberger Christian Slugovc Franz Stelzer 《Journal of molecular catalysis. A, Chemical》2003,200(1-2):11-19
The kinetic study of ring-opening metathesis polymerization (ROMP) of a diester functionalised norbornene derivative, (±)-exo,endo-bicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic acid diethyl ester, with a series of ruthenium benzylidene complexes revealed the applicability of these initiators for well defined polymerization reactions. Values for the rate of initiation as well as the rate of propagation of the initiators were determined and correlated to the molecular weight and polydispersity of the isolated polymers. As the only initiator providing an entry to virtually monodisperse polymers the classical “first generation Grubbs-catalyst” was identified, while N-heterocyclic carbene based initiators polymerized with a rate of propagation much higher than the rate of initiation yielding polymers with a broader molecular weight distribution. 相似文献
160.
New Rhenium Complexes Containing Trichalcogenido and Tetrachalcogenido Chelate Ligands The reactions of Cp*ReCl4 with polychalcogenide salts such as Na2S4 or (NEt4)2Se6 lead initially to the violet trichalcogenido chelate complexes Cp*ReCl2(E3) (E = S ( 3a ), Se ( 3b )) which, due to their functional chloro ligands, can be used as intermediates for further reactions. Upon hydrolysis in moist solvents or aminolysis with tert. butylamine 3a, b are converted into the tetrachalcogenido chelate complexes Cp*Re(O)(E4) (E = S ( 4a ), Se ( 4b )) and Cp*Re(NtBu)(E4) (E = S ( 5a ), Se ( 5b )), respectively. X-Ray structure analyses were carried out for the three mononuclear cyclo-oligoselenido compounds 3b–5b . It appears that the size of the Se2?n chelate ring (n = 3 or 4) essentially depends on steric factors within the coordination sphere of rhenium. 相似文献