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101.
L. Weber C. A. Mast M. H. Scheffer H. Schumann S. Uthmann R. Boese D. Bläser H.-G. Stammler A. Stammler 《无机化学与普通化学杂志》2000,626(2):421-429
Synthesis, Structure, and Reactivity of Functionalized Stibanido Complexes of Iron and Ruthenium [(η5-C5Me5)(CO)2MSbR1R2] (M = Fe, Ru; R1, R2 = SiMe3, C(O) t Bu, C(O)Ph, C(O)-1 Ad) The reaction of equimolar amounts of [(η5-C5Me5)(CO)2RuSb(SiMe3)2] ( 1 b ) and the carboxylic chlorides RC(O)Cl (R = tBu, Ph, 1-adamantyl) afforded the acyl(trimethylsilyl)stibanido complexes [(η5-C5Me5)(CO)2RuSb · {C(O)R}(SiMe3)] 2 b (R = tBu), 4 b (R = Ph), and 6 b (R = 1-Ad). The treatment of 1 b with two molar equivalents of pivaloyl chloride and benzoyl chloride led to the diacylstibanido complexes [(η5-C5Me5)(CO)2RuSb{C(O)R}2] ( 3 b , 5 b ). Analogously, the iron complex [(η5-C5Me5)(CO)2FeSb · (SiMe3)2] ( 1 a ) is converted into the corresponding diacylstibanido complexes 3 a (R = tBu), 5 a (R = Ph) and 7 a (R = 1-Ad) by an excess of acid chloride. The treatment of 1 a with equimolar amounts of RC(O)Cl gave inseparable mixtures of starting material and the monoacyl- and diacyl stibanido complexes. Oxalyl chloride reacted quantitatively with two equivalents of 1 a to give complex [{(η5-C5Me5) · (CO)2FeSb(SiMe3)C(O)}2] ( 8 ). The molecular structures of 1 a , 2 b and 5 b were elucidated by single crystal X-ray analyses. 相似文献
102.
103.
Ralf Steudel Oliver Schumann Jürgen Buschmann Peter Luger 《Angewandte Chemie (International ed. in English)》1998,37(4):492-494
Not the expected insertion into a S−S bond but rather substitution of one NR unit takes place in the reaction of [Cp2Ti(CO)2] with cyclic tetrasulfurdiimides 1,4-S4(NR)2. The product obtained contains the novel ligand S4NR and serves as precursor in the synthesis of small SN heterocycles not accessible before (see below). 相似文献
104.
Herbert Schumann Frank Girgsdies Sebastian Dechert Jochen Gottfriedsen Markus Hummert Stefan Schutte Joachim Pickardt 《无机化学与普通化学杂志》2002,628(12):2625-2630
The length of weak dative bonds in donor functionalized organo aluminum alkoxides [R2Al—O—R'—Y]2 (Y = NR2, OR, SR) show a temperature dependence in the solid state that is distinctively different from the common effect of libration. This observation is interpreted as being caused by thermal excitation. The possible general relevance of this phenomenon for the study of very weak bonds in molecular systems is discussed. 相似文献
105.
Herbert Schumann Frank Erbstein Dirk F. Karasiak Igor L. Fedushkin Jrg Demtschuk Frank Girgsdies 《无机化学与普通化学杂志》1999,625(5):781-788
The stepwise reaction of Me2SiCl2 with K[C5H3 tBuMe‐3] or Li[C9H7] and then with K[C9H6CH2CH2‐ NMe2‐1] followed by double deprotonation with NaH or LiBu, yields the two dimethylsilicon bridged cyclopentadienyl‐indenyl and indenyl‐indenyl donor‐functionalized ligand systems K2[(C5H2 tBu‐3‐Me‐5)SiMe2(1‐C9H5CH2CH2NMe2‐3)] ( 1 ), and Li2[(1‐C9H6)SiMe2(1‐C9H5CH2CH2NMe2‐3)] ( 2 ), respectively. Treatment of 1 with YCl3(THF)3, SmCl3(THF)1.77, TmI3(DME)3, and LuCl3(THF)3 gives the mixed ansa‐metallocenes [(C5H2 tBu‐3‐Me‐5)SiMe2(1‐C9H5CH2CH2NMe2‐3)]LnX (X = Cl, Ln = Y ( 3 ), Sm ( 4 ), Lu ( 5 ); X = I, Ln = Tm ( 6 )), respectively. The reaction of 2 with LuCl3(THF)3 yields [(1‐C9H6)SiMe2(1‐C9H5CH2CH2NMe2‐3)]LuCl ( 7 ). Compound 4 reacts with LiMe to give the corresponding alkyl derivative [(C5H2 tBu‐3‐Me‐5)SiMe2(1‐C9H5CH2CH2NMe2‐3)]Sm(CH3) ( 8 ). The new complexes were characterized by elemental analyses, MS spectrometry, and NMR spectroscopy. The molecular structures of 5 and 6 were determined by single crystal X‐ray diffraction. 相似文献
106.
Wagner B Schumann D Linne U Koert U Marahiel MA 《Journal of the American Chemical Society》2006,128(32):10513-10520
Heterocycles display common structural motifs in nonribosomally produced peptides with an enormous impact on their bioactivity. In the case of the branched cyclic Bacitracin A, the thiazoline moiety is manufactured during NRPS peptide chain elongation. Here we describe a method to selectively alter the heterocyclic metal binding subunit of Bacitracin A by the synthesis of heterocyclic building blocks that were successfully coupled to the linear decapeptide and subsequently cyclized using the excised bacitracin PCP-TE bidomain. Utilization of this cyclase allowed the first generation of branched cyclic bacitracin derivatives containing thiazole and oxazoles. The generated bacitracin derivatives showed bactericidal activity, indicating the possibility of altering the biological important heterocyclic subunit and overcoming existing limitations for the application of bacitracin. 相似文献
107.
There is a large number of optimisation problems in theoretical and applied finance that are difficult to solve as they exhibit
multiple local optima or are not ‘well-behaved’ in other ways (e.g., discontinuities in the objective function). One way to
deal with such problems is to adjust and to simplify them, for instance by dropping constraints, until they can be solved
with standard numerical methods. We argue that an alternative approach is the application of optimisation heuristics like
Simulated Annealing or Genetic Algorithms. These methods have been shown to be capable of handling non-convex optimisation
problems with all kinds of constraints. To motivate the use of such techniques in finance, we present several actual problems
where classical methods fail. Next, several well-known heuristic techniques that may be deployed in such cases are described.
Since such presentations are quite general, we then describe in some detail how a particular problem, portfolio selection,
can be tackled by a particular heuristic method, Threshold Accepting. Finally, the stochastics of the solutions obtained from
heuristics are discussed. We show, again for the example from portfolio selection, how this random character of the solutions
can be exploited to inform the distribution of computations. 相似文献
108.
Friederike Kramer Dieter Klemm Dieter Schumann Nadine Heßler Falko Wesarg Wolfgang Fried Dietmar Stadermann 《Macromolecular Symposia》2006,244(1):136-148
Summary: Using a “never-dried” procedure (according to Figure 4) shaped bacterial nanocellulose (BC, 1% cellulose, 99% water) has been modified by the formation of BC-polymer composites. For this purpose, acrylate and methacrylate monomers and methacrylate crosslinkers were photopolymerized inside an ethanol-swollen nanofiber network. Using the ethanol as solvent and as confirmed by model reactions the synthetic polymer (SP) part of the composites is constructed of crosslinked polymers (number of repeating units in the range of 500). As part of ongoing work on the development of (bio)materials from the innovative pool of BC composites these investigations are recently directed towards the creation of collagen-like materials. Thus, for these purposes, mainly water absorption capacity, strength, and elasticity have to be controlled, whilst still retaining essential features of BC like shape, nanofiber network, pore system, and proved biocompatibility. Using acrylic acid, 2-ethylhexyl acrylate, 2-hydroxyethyl methacrylate, N-vinyl pyrrolidone as acrylate monomers and triethylene glycol dimethacrylate and 1,4-butandiol dimethacrylate as crosslinkers of different concentrations either a filling of the pores or a coating of the fibers in the BC nanocomposites could be achieved. The small cellulose content of the composites significantly increases the water absorption value and the strength of the material as well as the ability of re-swelling in the case of fiber coated composites. Sample 12 is an optimized BC-SP composite regarding important properties of hyaline cartilage like Young's modulus in the range of 5–20 MPa using the well-known Simplex-method. 相似文献
109.
Tetramethylcyclopentadienyl complexes of magnesium, calcium and strontium are efficient catalysts at −78 °C for the solution polymerization of polar monomers such as alkyl methacrylates in the presence of only small amounts of triethylaluminium as cocatalyst. The molecular mass of the resulting polymers is predictable on the monomer/catalyst ratio. The polymerization reaction follows a first order kinetics with respect to the initial catalyst concentration. Block-copolymers are easily available by sequential dosage of the monomer. A living polymerization mechanism is proposed involving activation of the catalyst by alkylation and subsequent insertion of coordinated monomers. 相似文献
110.