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91.
Hartmut Schenkluhn Roland Berger Bernd Pittel Manfred Zähres 《Transition Metal Chemistry》1981,6(5):277-287
Summary The property-specific ligand control of 28 ligands on the decomposition temperatures in solution, measured by d.t.a. of a four-coordinate nickel(II)-complex is reported. A quantitative separation of electronic and steric effects by a multilinear regression analysis (75% electronic and 25% steric influence for the chosen ligands) is presented. The controlling effect of the selectivity on the decomposition (fraction of the C-C-linked product) (25 P-ligands) leads to an electronic: steric ratio of the property-specific ligand control of 5545 for the chosen ligands. An increase in the relative acceptor character of the P-ligands relatively destabilizes the complexes and thereby favours formation of a C-C-bond. An increase in steric hindrance also favours C-C-bond formation. A method for revising the steric parameter of P-ligands is presented and is used to correct the -value of (PhCH2)3P is corrected to 135°. SCCC-MO-calculations for testing the chemical reasoning of the separated electronic and steric ligand property control are shown. 相似文献
92.
Manfred Schreiner Peter Ettmayer Richard Kieffer 《Monatshefte für Chemie / Chemical Monthly》1982,113(8-9):869-876
Molybdenum-tungsten-carbonitrides can be prepared by reacting prealloyed powders of Mo and W with carbon in the presence of nitrogen or ammonia. Single phase carbonitrides (Mo, W) (C, N) with the WC-type structure can be obtained. The nitrogen content of these carbonitrides increases with increasing molybdenum content. Flowing ammonia has a decarburizing effect, which has to be counterbalanced by an addition of a carbonaceous gas such as methane. Nitrogen instead of ammonia is equally effective and gives carbonitrides which have a nitrogen content only insignificantly lower than the carbonitrides obtained in flowing ammonia. The lattice parameters of the carbonitrides are found to be slightly smaller than the lattice parameters of the corresponding carbides. 相似文献
93.
The synthesis and the photochemical behaviour of 4 new 2H-1.4-oxazines and 3 new spiro-2H-1.4-oxazines is described. 相似文献
94.
95.
The [4 + 2] cycloaddition stereoselectivity of dienamines 1–4 with dimethyl fumarate and fumaronitrile has been investigated, and functionalised decalins 21–40 have been prepared by elimination of Me2NH from cycloadducts 7–11 and 15–20 ; in the context of the synthesis of drimane sesquiterpenes, the reduction of dienediesters 29 and 30 is also described. 相似文献
96.
Boris Mahltig Jean-François Gohy Sayed Antoun Robert Jérôme Manfred Stamm 《Colloid and polymer science》2002,280(6):495-502
This paper reports on the pH-dependent adsorption of weak the polyelectrolytic diblock copolymer poly(2-vinylpyridine)-block-poly(dimethylaminoethyl methacrylate), (PVP-b-PDMAEMA). Aqueous PVP-b-PDMAEMA solutions have been adsorbed on alkaline pretreated silicon substrates. Altogether two copolymers differing in block ratio and molecular weight were used for the investigations. While the electrical charge of both samples in solution was investigated by electrophoretic measurements, the adsorbed polymer layers were studied with ellipsometry and atomic force microscopy (AFM). Depending on pH the electrical charge of both blocks of the diblock copolymer varied. Three different regimes have been identified. Under acidic conditions at pH<5, both blocks are mainly positively charged. At medium pH between 5 and 8, only the PDMAEMA block is positively charged. At pH>8, both blocks are nearly uncharged and a polymer precipitation occurred in solution. Each of these pH regimes was characterized by a specific adsorption behaviour leading to two adsorption maxima at acidic and alkaline pH values, while at medium pH a plateau in the adsorbed amount was observed. Moreover, the structures of the polyelectrolytes formed on the substrate after adsorption were specific to each of the three pH regimes. 相似文献
97.
Manfred Schlosser 《Angewandte Chemie (International ed. in English)》1974,13(11):701-706
Merits and drawbacks of known carbon-carbon linking procedures are outlined. Two novel methods are discussed in some detail: the copper-catalyzed alkylation of Grignard reagents and reactions with allylpotassium compounds. Both methods provide a very efficient access to saturated, unsaturated, as well as functionally substituted hydrocarbons and moreover permit an astonishing degree of regio- and stereoselective control of olefin synthesis. 相似文献
98.
During the examination of extracts from Oncinotis tenuiloba STAPF a new polyamine, N4-benzoylsperimidine ( 8 ), was isolated. For unambiguous structure elucidation, it was transformed into the diacetyl derivative 13 , and the three possible N-benzoyl-substituted isomers of spermidine 5, 8 , and 11 together with their peracetylated derivatives 12–14 , respectively, were synthesized and identified. 相似文献
99.
A bidentate ligand consisting of a 2-(diphenylphosphinoethyl)-thio moiety was attached to β-cyclodextrin at the 6-position. The corresponding norbornadiene Rh(I) complex in the form of the BF4− salt was prepared. 相似文献
100.
Wolfgang A. Herrmann Ricardo Serrano Adolf Schäfer Ulrich Küsthardt Manfred L. Ziegler Ernst Guggolz 《Journal of organometallic chemistry》1984,272(1):55-71
Short-wavelength photolysis of tricarbonyl(η5-pentamethylcyclopentadienyl)rhenium (1) (λ < 300 nm, quartz-glass) in tetrahydrofuran yields under partial or complete decarbonylation three novel organorhenium compounds, with the relative yields depending upon the irradiation time. Formed by exhaustive oxidative decarbonylation, the complex trioxo(η5-pentamethylcyclopentadienyl)rhenium(VII) (5) represents the first example of the new class of oxo half-sandwich complexes. The derivatives (μ-O)[(η5-C5Me5)Re(CO)2]2 (2; Me = CH3) and (η5-C5Me5)2Re2(CO)2O2 (3; Me = CH3) containing both oxo and carbonyl ligands are formed from 1 at shorter irradiation times. Both compounds are isolable intermediates along the mechanistically not yet fully established sequence 1 → → 5 as they are degraded to 5 under CO2 elimination in the presence of air and/or light. The mixed oxo carbonyl complex 2 has been characterized by means of single-crystal X-ray diffraction techniques (triclinic, space group P-Ci1; a 907.4(2), b 1040.2(3), c 1414.3(4) pm; α 79.99(2), β 88.42(2), γ 66.18(2)°; Riso = 0.068, Raniso = 0.037, Rw = 0.031). The molecular structure centres around an isosceles Re2O triangle whose metal centres exhibit a strongly distorted square-pyramidal geometry; the metal-metal distance recorded at 281.7(1) pm is in agreement with a single bond by the EAN rule. The centrically coordinated, planar five-membered ring ligands are parallel to each other (interplanar angle 2°) and occupy trans-positions with respect to the central Re2O geometry. 相似文献