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51.
The equilibrium between Co2(CO)8 and Co4(CO)12 has been investigated in hexane solution in the temperature range 105–145°C under carbon monoxide pressure (6–14 bar). the data obtained by infrared analytical monitoring of the system in a high-pressure cell alow a reasonably precise extension of the calculated equilibrium concentration between —20 and 300°C. The thermo- dynamic parameters obtained for this system are: ΔH0 29.5 ± 0.5 kcal mol-1, ΔS0 135 ± 3 cal mol-1 K-1. The stability regions of Co2(CO)8 and Co4(CO)12 in terms of p(CO) and temperature are discussed.  相似文献   
52.
Iron(II) complexes containing CNBX?3 or CNBX2NC? ligands were prepared from the reaction of K[(π-C5H5)Fe(CO)(CN)2] with boranes (BX3; X = F, Cl, Br H, Ph). Stable, twelve-membered ring compounds containing Fe, C, N, and B atoms were formed involving CNBF2NC? and CNBBr2NC? ligands. The reaction of K[(π-C5H5)Fe(CO)(CN)2] with AlCl3 gave a four-center complex with two Fe and two Al atoms. The compounds were studied by infrared and mass spectroscopic methods.  相似文献   
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We report an expedient approach to highly functionalized cis‐ and trans‐decalines that could function as key structural subunits toward the synthesis of various classes of terpenoids. Key to the strategy is an organocatalyzed Robinson annulation reaction of the Nazarov reagent that affords chiral enone building blocks with high enantioselectivities. The quaternary carbon stereogenic center can direct the subsequent reactions and allow the rapid and diastereoconvergent assembly of complex decalines with contiguous stereocenters.  相似文献   
56.
Several cinchona based squaramide catalysts were applied to the asymmetric Michael addition of α-nitroethylphosphonates to acrylic acid aryl esters, resulting in high yields and enantioselectivities. The absolute configuration of one of the quaternary α-nitrophosphonate adducts was deduced from its experimental and calculated CD spectra. The adducts were reduced to their cyclic aminophosphonates by catalytic hydrogenation.  相似文献   
57.
Diarylethenes possess unique structural properties, which enabled them to find widespread applications in the field of photochromism. Nowadays, bisthienylcyclopentenes (BTCs) present the most popular subfamily of these compounds, which are widely used as P‐type chromophores. This minireview summarises the main strategies for the synthesis of symmetrical and nonsymmetrical BTCs. In addition, attention is drawn to desymmetrisations achieved by monosubstitutions, which is not frequently utilised, although it can be highly advantageous. This is supported with some of the authors’ latest results.  相似文献   
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In Korchmáros et al. (2018)one-factorizations of the complete graph Kn are constructed for n=q+1 with any odd prime power q such that either q1(mod4) or q=2h?1. The arithmetic restriction n=q+1 is due to the fact that the vertices of Kn in the construction are the points of a conic Ω in the finite plane of order q. Here we work on the Euclidean plane and describe an analogous construction where the role of Ω is taken by a regular n-gon. This allows us to remove the above constraints and construct one-factorizations of Kn for every even n6.  相似文献   
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Abstract

Trialkyl phosphites are known to react with α-halogenoketones to yield β-ketophosphonates (Arbuzov product) or vinyl phosphates (Perkow product) according to coniiitions.1 α-Hydroxyphosphonate may be formed in addition, in prcltic media.2 We have now shown that none of these products is formed in the presence of silver perchlorate (in benzene sclutim); nor could we detect the ketophosphonium perchlorate reported previously. Phosphorus-31 nmr showed the formation of trimethyl phosphate and tetramethyl pyrophosphate as the exclusive phosphorus-containing products. The sequence of possible reaction is complex and the overall stoichiometry may vary somewhat according to the rate and order of rixing. Trialkyl phosphate could be formed by elimination of alkyne from vinyloxyphosphonium intermediate produced together with silver iodine in first stage of the interaction. Pyrophosphate formation would then result from nucleophilic attack of trimethyl phosphate on the trimethoxy(1-nethylvinyloxy)phosphoniun ion, which may be formed as a reactive intermediate. Evidence for formation of methyl perchlorate in the final dealkylation of the quasiphosphonium intermediate is provided by proton nmr spectroscopy and by the formation of the N-methylquino-linium salt on addition of quinoline. No change in the 31P nmr spectrum occurs at this stage. Other by-products of the main reactions include the dehalogenated ketone (acetone from iodoacetone or acetnphenone from α-iodoacetophenone).  相似文献   
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