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1.
Transformations of the edge-bridged double cubane cluster [(Cl4cat)2(Et3P)2Mo2Fe6S8(PEt3)4] (1) under reducing conditions have been investigated as synthetic approaches to the clusters of nitrogenase. Cluster 1 is a versatile precursor to different Mo-Fe-S cluster types. The reaction system 1/K(C14H10) in THF yields the reduced cluster [(Cl4cat)2(Et3P)2Mo2Fe6S8(PEt3)4]1- (2), which as its crystalline Et4N+ salt retains the edge-bridged structure of 1. X-ray structural and M?ssbauer spectroscopic results indicate an unsymmetrical electron distribution with localized [MoFe3S4]2+,1+ cubane-type units. The system 1/2K(C14H10)/2HS- in THF/acetonitrile affords [(Cl4cat)4(Et3P)4Mo4Fe12S20K3(DMF)]5- (3), whose structure was determined as the Ph3PMe+ salt. The cluster consists of two isostructural Mo2Fe6S9 fragments connected by two mu 2-S bridges. Three potassium ions are bound between the two fragments. In each fragment, the iron atoms are present in tetrahedral FeS4 and the molybdenum atoms in octahedral MoO2PS3 coordination units, and two MoFe3(mu 3-S)3 cuboidal units are bridged by a common mu 6-S atom. The fragments have idealized mirror symmetry and are isostructural with two of the fragments present in the previously reported high-nuclearity cluster [(Cl4cat)6(Et3P)6Mo6Fe20S30]8- (4) (Osterloh, F.; Sanakis, Y.; Staples, R. J.; Münck, E.; Holm, R. H. Angew. Chem., Int. Ed. Engl. 1999, 38, 2066). On the basis of overall shape, atom connectivities, and metric features, the Mo2Fe6S9 fragment is a topological analogue of the P-cluster of nitrogenase in the PN (reduced) state. A third cluster type, formed as a minor byproduct in the reaction system leading to 2, was crystallographically identified as [(Cl4cat)2(Et3P)2Mo2Fe6S8(PEt3)4]4-, whose core is made up of two MoFe3(mu 3-S)3 cuboidal units bridged by two mu 2-S atoms and connected by a direct Fe-Fe bond. Full structural details and the redox properties of 2 and 3 are reported.  相似文献   

2.
In this study, three novel tetranuclear nickel(II) cubane-type clusters with the general formula [Ni4(L)43-CH3O)4(CH3OH)4] [L: the anion of 5-methyl-2-hydroxybenzaldehyde (1), 2-hydroxypropiophenone (2), and 2-hydroxybenzophenone (3)] were synthesized and characterized by single-crystal X-ray diffraction analysis. The crystal structure of each compound contains a tetranuclear cubane core [Ni4O4] based on an approximately cubic array of altering nickel and oxygen atoms with intracluster metal–metal separations of 3.04–3.14 Å. Each Ni(II) atom is surrounded by two oxygen atoms from the ligand (L) and by the μ3-CH3O oxygen atom that bridges three Ni atoms of the cubane core. The coordination sphere of Ni is completed with one methanol molecule and making six-coordinate with a distorted octahedral geometry. These complexes were characterized also by spectroscopy (IR and UV–Vis). Simultaneous TG/DTG–DTA techniques were used to analyze their thermal behavior under inert atmosphere, with particular attention to determine their thermal degradation pathways, which was found to be a multi-step decomposition accompanied by the release of the ligand molecules. Finally, the kinetic analysis of the decomposition processes was performed for the first step of complex (3), since only this verifies the requirement of applying an isoconversional method like Kissinger–Akahira–Sunose (KAS). For this step, we found the average value E a = 107.8 ± 4.5 kJ mol?1.  相似文献   

3.
Reactions are reported of sulfur-bridged incomplete cubane-type tungsten clusters having W(3)(micro(3)-S)(micro-S)(3) cores with acetylene and its derivative dimethylacetylenedicarboxylate (DMAD). The reaction of the isothiocyanate tungsten cluster [W(3)(micro(3)-S)(micro-S)(3)(NCS)(9)](5)(-) (5) with acetylene in 0.1 M HCl afforded a novel complex having two acetylene molecules in different adduct formation modes, [W(3)(micro(3)-S)(micro(3)-SCH=CHS)(micro-SCH=CH(2))(NCS)(9)](4)(-) (6), and the presence of two kinds of intermediates [W(3)(micro(3)-S)(micro-S)(micro(3)-SCH=CHS)(NCS)(9)](5)(-) (7) and [W(3)(micro(3)-S)(micro-S)(2)(micro-SCH=CH(2))(NCS)(9)](4)(-) (8) was observed. The reaction of the diethyldithiophosphate (dtp) tungsten cluster [W(3)(micro(3)-S)(micro-S)(3)(micro-OAc)(dtp)(3)(CH(3)CN)] (10) with DMAD in acetonitrile containing acetic acid resulted in the formation of another complex having two DMAD molecules of different adduct formation modes, [W(3)(micro(3)-S)(micro-SC(CO(2))=CH(CO(2)CH(3)))(micro(3)-SC(CO(2)CH(3))=C(CO(2)CH(3))S)(micro-OAc)(dtp)(3)] (11), where hydrolysis of one of the four ester groups of the two DMAD groups occurred and the resultant carboxylic group coordinated to tungsten. The conformation of the micro-SCH=CH(2) moiety in 6 is different from that of the corresponding moiety in [W(3)(micro(3)-S)(micro-O)(micro-S)(micro-SCH=CH(2))(NCS)(9)](4)(-) (4). Introduction of the second acetylene molecule to the intermediate [W(3)(micro(3)-S)(micro-S)(2)(micro-SCH=CH(2))(NCS)(9)](4)(-) (8) resulted in the formation of 6. The clusters were characterized by UV-vis spectroscopy, (1)H NMR spectroscopy, and X-ray crystallography (for (Hpy)(4).6.1.33py.0.5H(2)O and 11.CH(3)CN), and the formation of 6 and 11 was examined in detail from a mechanistic point of view.  相似文献   

4.
Synthesis and reactions of 5 ,8-epidioxyandrost-6-enes   总被引:1,自引:0,他引:1  
  相似文献   

5.
Condensation of 3-acetyl-8-ethoxycoumarin (3) with thiosemicarbazide gave ethylidenehydrazinecarbothioamide 5, which was transformed into the thiazolidin-4-one derivatives 6,7. Interaction of 3 with DMF/POCl(3) gave b-chloroacroline derivative 8. Treatment of 3 with malononitrile gave benzo[c]chromone and 2-aminobenzonitrile derivatives 9 and 10, respectively with respect to the reaction conditions. Condensation of 3-(2-bromoacetyl)-8-ethoxycoumarin (4) with o-phenylenediamine gave 3-(quioxaline-2-yl)-8-ethoxycoumarin hydrobromide (11), while 4 reacted with 2-aminopyridine to give chromenopyridopyrimidine derivative 12. Condensation of 4 with potassium thio-cyanate/methanol gave an unexpected derivative, 2H-chromeno-3-carboxy(methyl-carbonimidic)thioanhydride 16, which upon treatment with (NH(2))(2)·H(2)O gave 3-ethoxy-2-hydroxybenzaldehyde azine 19. Interaction of 4 with thiourea derivatives gave thiazole derivatives 20a-c. The structures of the newly synthesized compounds were confirmed by their spectra data. The newly synthesized compounds were also screened for their antimicrobial activity.  相似文献   

6.
The mixed-metal cubane-type clusters [(Cp*Mo)3(mu3-S)4RuH2(PR3)][PF(6)] [Cp* = eta5-C5Me5; R = Ph (2), Cy (5)] were effective for the N-N bond cleavage of hydrazine and phenylhydrazine via a disproportionation reaction. The ammonia cluster [(C*Mo)3(mu3-S)4Ru(NH3)(PPh3)][PF6] (3) and/or the unprecedented double-cubane-type cluster with bridging nitrogenous ligands [{(Cp*Mo)3(mu3-S)4Ru}2(mu2-NH2)(mu2-NHNH2)][PF6]2 (4) were isolated from the reaction mixtures, and their structures were determined by X-ray diffraction studies.  相似文献   

7.
The syntheses of homogeneous cyclodextrin-based carbohydrate clusters, persubstituted with beta-D-thioglucosyl or D-thiolactosyl residues on either (a) the primary face, (b) the secondary face, or (c) both the primary and the secondary faces of their cyclodextrin tori, are described. The key step in the synthetic methodology, namely the attachment of the carbohydrate residues to the cyclodextrin torus, proceeds in moderate-good yields (42-70%) by the photoaddition of thiol groups, positioned at the anomeric centers of the carbohydrate residues, to allyl ether functions on the cyclodextrins. Facile removal of protecting groups then affords the free cluster compounds. Extensive 1-D and 2-D NMR spectroscopic investigations were performed on these compounds to determine their structures and establish their homogeneities, and a brief computer molecular modeling study allowed estimates of the dimensions of the clusters to be determined.  相似文献   

8.
By oxidative cyclization of 5,5′-arylmethylenebis(6-methylaminouracil) derivatives with diethyl azodicarb-oxylate a number of 5-deazaisoalloxazines were synthesized having at the C(8) position a substituent that causes a bathochromic shift varying between 20 and 130 nm, depending on the substituent. To increase the solubility in aqueous media 8-substituted 5-deazaflavins were prepared having a carboxymethyl group at the N(3) position. The carboxymethyl group was introduced prior to the oxidative cyclization.  相似文献   

9.
10.
Aminoboranes are synthesized in situ from the reaction of the corresponding lithium aminoborohydrides (LABs) with methyl iodide, trimethylsilylchloride (TMS-Cl), or benzyl chloride under ambient conditions. In hexanes, the reaction using methyl iodide produces aminoborane and methane, whereas in tetrahydro-furan (THF) this reaction produces amine-boranes (R1R2HN:BH3) as the major product. The reaction of iPr-LAB with TMS-Cl or benzyl chloride yields exclusively diisopropylaminoborane [BH2-N(iPr)2] in THF as well as in hexanes at 25 degrees C. Diisopropylaminoborane and dicyclohexylaminoborane exist as monomers due to the steric requirement of the alkyl group. All other aminoboranes studied are not sterically hindered enough to be monomers in solution, but instead exist as a mixture of monomers and dimers. The dimers are four-membered rings formed through boron-nitrogen coordination. In general aminoboranes are not hydroborating reagents. However, monomeric aminoboranes, such as BH2-N(iPr)2, can reduce nitriles in the presence of catalytic amounts of LiBH4. This BH2-N(iPr)2/LiBH4 reducing system also re-duces ketones, aldehydes, and esters. Diisopropylaminoborane, synthesized from iPr-LAB, can be converted into boronic acids by a palladium-catalyzed reaction with aryl bromides. Aminoboranes derived from heterocyclic amines, such as pyrrole, pyrazole, and imidazole, can be prepared by the direct reaction of borane/tetrahydrofuran (BH3:THF) with these heterocyclic amines. It has been reported that pyrazole-derived aminoborane forms a six-membered dimer through boron-nitrogen coordination, where as, pyrrolylborane forms a dimer through boron-hydrogen coordination. Pyrrolylborane monohydroborates both alkenes and alkynes at ambient temperatures. Hydroboration of styrene with pyrrolylborane followed by hydrolysis gives the corresponding boronic acid, 2-phenylethylboronic acid, in 40% yield. Similarly phenylacetylene is mono-hydroborated by pyrrolylborane, to give E-2-phenylethenylboronic acid in 50% yield.  相似文献   

11.
12.
13.
The cotrimerization of phenylacetylene and diethynylbenzene yields high molecular weight highly branched polyphenyls. The polymers obtained have the usual thermal stability. They are soluble in common chlorinated solvents.  相似文献   

14.
Brominations of mono addition products of 1,4-cyclohexadiene with 2,4-dinitrobenzenesulfenyl chloride (RSCl) selectively gave 1R(S),2R(S),4R(S),5R(S)-4,5-dibromo-2-(2,4-dinitrophenylthio)cyclohexyl acetate and 1R(S),2R(S),4R(S),5R(S)-4,5-dibromo-2-chlorocyclohexyl)(2,4-dinitrophenylthio)sulfane. From series reactions 7-oxabicyclo[4.1.0]hept-3-ene with reagents, such as RSCl, NaN3, and H2SO4/Ac2O, six 1,2,4,5-tetrasubstituted cyclohexane derivatives including S, O, N, Cl, and Br were selectively obtained. Formations and structures of the products were discussed.  相似文献   

15.
Ligand-exchange reactions involving octahedral W6S8 clusters and a family of pyridine-based ligands (isonicotinic acid, isonicotinamide, 4-hydroxypyridine, 4-aminopyridine, 4-pyridineacetamide) have been explored with the goal of preparing compounds that crystallize in hydrogen-bonded arrays. Two new compounds, W6S8(4-pyridineacetamide)6.DMF.4-pyridineacetamide (1) and W6S8(4-aminopyridine)6.4DMF (2), were isolated and characterized by single-crystal X-ray diffraction. Both compounds crystallize in the P2(1)/c space group with a = 16.461(1), b = 33.08(2), c = 13.165(10) A, beta = 103.270(15) degrees for 1 and a = 13.8988(5), b = 13.2791(5), c = 15.6293(6) A, beta = 108.5410(10) degrees for 2. Each compound was further characterized by 1H NMR spectroscopy, elemental (CHN) analysis, and thermogravimetric analysis. Examination of the structures shows that 1 forms a three-dimensional hydrogen-bonded network in which each 4-pyridineacetamide ligand interacts with ligands on neighboring clusters or with the free ligand of crystallization. This is the first hydrogen-bonded network formed from W6S8 clusters. In 2, the amino groups act as hydrogen-bond donors toward DMF molecules of crystallization, but an extended array is not formed. In addition, the binding strengths of these pyridine-based ligands to the W6S8 cluster were studied through quantitative 1H NMR studies of ligand-exchange reactions. A qualitative relationship was found between ligand binding strengths and Hammett substituent constants for this group of ligands.  相似文献   

16.
17.
3-Acetamidotropolone ( 1a ) reacted with bromine and fuming nitric acid to afford respectively 3-acetamido-7-bromo- ( 1b ) and -5,7-dibromotropolone ( 1c ) and 3-acetamido-5-nitrotropolone ( 1d ). Azo-coupling reaction of 1a gave 3-acetamido-5-(4-methylphenylazo)tropolone ( 1f ). Bromination of 1d and 1f gave 7-bromo-substituted compounds 1e and 1g , respectively. The compounds 1b-g were hydrolyzed to afford 3-aminotropolones 4b-g , which reacted with triethyl orthoformate to give the corresponding 8H-cyclohept[d]oxazol-8-ones 5b-g . Heating of 3-acetamidotropolones 1a-d with polyphosphoric acid gave 2-methyl-8H-cyclohept[d]oxazol-8-ones 6a-d .  相似文献   

18.
The mechanistic aspects of organic reactions catalyzed with palladium clusters and stoichiometric reactions of carbonyl and carbene clusters are discussed. Palladium carbonyl carboxylates Pd4(CO)4 (OCOR)4(RMe, CMe3, Ph, CF3, CCl3) undergo thermolysis above 110–130°C, giving rise to CO2, CO and diacyls. In solutions of aromatic compounds the insertion of carbon dioxide into the aromatic CH bond or activated CH bond of alkylaromatic compounds was observed in the course of the thermolysis. The decomposition of palladium carbene carboxylate cluster Pd4(Ph2C)4(OAc)4 at 80°C has been found to involve inner sphere carbene oxidation during which an oxygen atom is transferred from the carboxylate group to the carbene ligand. Analogously, the reaction of [Pd(OAc)2PPh3]2 with formic acid, a reaction involving intermediate cluster formation, includes the transfer of an oxygen atom from the formate droup to the P atom of a phosphorus containing ligand, supposedly a diphenylphosphido bridging group. Positional and geometric α-alkene isomerization in aqueous PdCl2−2 solution has been found to be catalyzed by palladium (I) complexes of type Pd2Cl2−4. Colloidal clusters containing more than 500 palladium atoms in the metal core, which are soluble in polar organic solvents, have been found to catalyze the oxidative reactions of alkenes, toluene, alcohols and formic acid. Alcohols bearing at least one hydrogen atom in α-position undergo dehydration under mild conditions in non-acidic solution containing a Pd, Mo octanuclear anionic cluster [Pd4Mo4(CO)12Cp]2−. The reaction of benzyl alcohol gives rise to trans-stilbene. All these catalytic reactions can be rationalized within a scheme including the oxidative addition of the substrates across cluster metal-metal bond as a key step.  相似文献   

19.
20.
We have examined the reactivity and saturation of small gold clusters (cations, neutrals and anions) towards several molecules and find that specific small gold clusters exhibit a pronounced variation in their reactivity towards hydrogen, methane and oxygen. The reactivity not only depends strongly on cluster size but also on the cluster charge state. For example, small (n<15) gold cations react readily with D2, but no evidence of reaction is observed for the anions under our experimental conditions. Similar behavior is seen for methane. With oxygen only even atom (odd electron) anions are reactive, and Au 10 + is the only cation which exhibits evidence of reaction. The global features (small cluster cations reactive towards H2, CH4, but large ones not reactive, odd electron anions reactive towards O2) are qualitatively explained by appealing to a simple frontier orbital picture. The uptake of deuterium and methane on gold clusters also exhibits a pronounced size dependence with D/Au varying from a high of 3 for the dimer to zero for clusters containing more than 15 Au atoms. Comparison of the methane and deuterium saturation behavior leads us to suggest that methane is dissociated and bound as CH3 and H.  相似文献   

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