Two series of redox-active, iron−sulfur core dendrimers of the general structure (nBu4N)2Fe4S4(S-Dend)4 (Dend = dendrons of generations 1 through 4) were prepared. Heterogeneous electron-transfer ...rate constants indicated that the rigid series of dendrimers were more effective at attenuating the rate of electron transfer than were the flexible series of dendrimers. These results were rationalized using computationally derived models which indicated an offset and mobile iron−sulfur core in the flexible series of molecules and a more central and relatively immobile iron−sulfur core in the rigid series of molecules. Further consideration of these data indicated that, while the dendrimers containing rigid ligands had better encapsulated redox cores for a given molecular weight, these molecules had higher electron-transfer rates for a given molecular radius.
A High-Yielding Supramolecular Reaction Aakeröy, Christer B; Beatty, Alicia M; Helfrich, Brian A
Journal of the American Chemical Society,
12/2002, Letnik:
124, Številka:
48
Journal Article
Recenzirano
The X-ray crystal structure determinations of twelve cocrystals involving iso-nicotinamide and a variety of carboxylic acids have revealed a very consistent pattern of hydrogen-bond preferences. The ...combination of a monocarboxylic acid, an amide, and a pyridine moiety leads, in every case, to discrete “supermolecules” (consisting of two molecules of iso-nicotinamide and two molecules of the relevant carboxylic acid) with well-defined and robust connectivity. The two dominant (regularly occurring) supramolecular synthons in these crystal structures are (1) the heteromeric carboxylic acid···pyridine hydrogen bond and (2) a self-complementary amide···amide hydrogen-bond interaction, both of which prevail in the presence of widely differing chemical functionalities. In four of these cocrystals, a dicarboxylic acid is employed, which alters the structural outcome from discrete entities to infinite assemblies (or to a hexameric complex in a “U-shaped” dicarboxylic acid), which is fully expected since the two primary supramolecular synthons remain intact. This structural study shows that iso-nicotinamide is a supramolecular reagent that can produce well-defined supermolecules (containing carboxylic acids) in very high yields.
The molybdenum nitrosyl complex Cp*Mo(NO)(CH2CMe3)(C6H5) reacts at room temperature via elimination of neopentane or benzene to form the transient species Cp*Mo(NO)(CHCMe3) and Cp*Mo(NO)(η-C6H4). ...These reactive intermediates effect the intermolecular activation of hydrocarbon C−H bonds via the reverse of the transformations by which they are generated. Thermolysis of Cp*Mo(NO)(CH2CMe3)(C6H5) in pyridine yields the adducts Cp*Mo(NO)(CHCMe3)(NC5H5) and Cp*Mo(NO)(η2-C6H4)(NC5H5), and the benzyne complex has been characterized by X-ray diffraction.
A series of novel cyclobutenodehydro(n)annulenes (n = 18, 24, 30) have been prepared as precursors in an organic approach to the cyclocarbons C{sub 18}, C{sub 24}, and C{sub 30}. On the way to these ...macrocycles, synthetic entries to three new classes of enediynes have been developed. Bis(1-propynyl)cyclopropenone was prepared in the reaction of 1-(trimethylsilyl)-1-propyne with trichlorocyclopropenylium tetrachloroaluminate. The 3,4-dialkynyl-3-cyclobutene-1,2-dionines were prepared by the reaction of 3,4-dichloro-3-cyclobutene-1,2-dione either with (tri-n-butylstannyl)alkynes in the presence of catalytic amounts of Pd(PPh{sub 3}){sub 4} or with the soluble copper (I) acetylides of (trialkylsilyl)acetylenes. The peculiar downfield resonances of the terminal acetylenic carbon atoms in the {sup 13}C NMR spectra of the 3,4-dialkynyl-3-cyclobutene-1,2-diones are discussed. The oxidative Hay coupling of the acetonide of 3,4-diethynyl-3-cyclobutene-1,2-diol or of the bis(ethylene ketal) of 3,4-diethynyl-3-cyclobutene-1,2-dione gave two series of cyclobutenodehydroannulenes with 18{pi}-, 24{pi}-, and 30{pi}-electron perimeters.
Radical recombination following the photodissociation of 2-hydroxy-4‘-(2-hydroxyethoxy)-2-methylpropiophenone in isotropic solution was monitored using time-resolved infrared spectroscopy. The rate ...of radical recombination was determined to decrease in the presence of a magnetic field of greater than 5 mT and to increase in the presence of a magnetic field smaller than 5 mT.
