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Results for “heterocycles”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Dinuclear Gold(I) Complexes Bearing Alkyl-Bridged Bis(N-heterocyclic carbene) Ligands as Catalysts for Carboxylative Cyclization of Propargylamine: Synthesis, Structure, and Kinetic and Mechanistic Comparison to the Mononuclear Complex [Au(IPr)Cl]

Eight new dinuclear gold(I) complexes, [Au 2 (L)X 2 ] (1–8), were synthesized using a straightforward synthetic procedure under very mild conditions. The complexes have been characterized by NMR spectroscopy, elemental analysis, and single-crystal X-ray structure analysis. Their catalytic activity was investigated in the carboxylative cyclization of propargylamine (PPA). A superior performance in comparison to [Au(IPr)Cl] (9) was obtained for complexes 1 and 2 having an eight-methylene bridge connecting two NHCs with an arene bearing an isopropyl substituent for X = Cl, Br. This prompted more detailed kinetic and mechanistic studies by FTIR comparing dinuclear complex 2 of X = Cl to complex 9. Fortuitously the FTIR studies allowed monitoring of the formation of the products carbamic acid (CA) and carbamate salt (CS), as well as a key cyclized intermediate first discovered by Ikariya. These data allow additional insight into the mechanism as well as the central role which may be played by Au(I) carbamate formation as a higher energy resting state present in the catalytic cycle. In conclusion, the crystal structures of four of the new complexes and a detailed computational study relevant to the role of carbamic acid (CA) and carbamates in the catalytic cycle are also reported.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Actinide tetra-N-heterocyclic carbene ‘sandwiches’

Highly-symmetrical, thorium and uranium octakis-carbene ‘sandwich’ complexes have been prepared by ‘sandwiching’ the An( iv ) cations between two anionic macrocyclic tetra-NHC ligands, one with sixteen atoms and the other with eighteen atoms.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

A small heterocyclic molecule as a multistate transistor: a quantum many-body approach

Weakly coupled molecular junctions are an active and important field of research due to their non-linear charge carrier transport. In this study, we investigate transport properties in a weakly coupled molecule, B 2 C 2 N 2 H 6 , using a combined quantum many-body approach and kinetic (master) equations. Various non-linear current–voltage characteristics such as negative differential conductance (NDC), rectifications, and Coulomb staircase, which are the hallmarks of multistate transport devices, have been obtained. We further explore the effect of different perturbations such as gate voltage and perpendicular magnetic field on molecular transport. Depending on the strength of the applied perturbing field, several phenomena such as current switching, and suppression of NDC, have been realized in the device. This study demonstrates small molecules as promising components in next-generation nano-devices.

36 MATERIALS SCIENCE↗
NASA NTRS1970

New hyperthermal thermosetting heterocyclic polymers

Polyimidazopyrrolone polymers, formed by the condensation of aromatic dianhydrides with aromatic tetraamines in various solvents, form moldings that resist degradation in air and retain great strength at 400 to 700 degrees F. The resins have good insulating properties, are easy to mold, and make good protective coatings.

Bilow, N.↗
NASA NTRS1971

Review of oxidative degradations of certain heterocyclic polymers

The curing and decompositions of polyphenylenes and several nitrogen-containing condensation polymers, particularly polybenzimidazoles and pyrones, are reviewed critically. It is concluded that the condensations are usually imperfect and incomplete and that in most of the published work the late stages of the condensation are complicated by the beginnings of the charring and carbonization processes. Most discussions of mechanisms in this range are highly speculative and of little value. The most promising fields for further research are at lower temperatures, where slow oxidation processes deserve study, and at higher temperatures, where it may be possible to influence carbonization processes to obtain better products.

Mayo, F. R.↗
NASA NTRS1972

Photochromism of heterocyclic systems

The preparations of photochromic dimers of a 2-aryl-4,5-di-phenylimidazyl radical and of a 2,5-diphenyl-3,4-isobenzopyrrole with different substituents in the homocyclic ring are reported. Of the dienes investigated, only 1-4-diphenyl-1,3-butadiene and 2,3-dimethyl-1,3-butadiene gave isolable amounts of the Diels-Adler adducts.

Silversmith, E. F.↗
NASA NTRS1971

Stabilities of nitrogen containing heterocyclic radicals and geometrical influences on non-radiative processes in organic molecules

Theoretical and experimental work on generating radicals by removal of a hydrogen atom from pyrrole, imidazole, indole, and carbazole is reported. Photophysical studies on indolizine and related aza-derivatives show that materials having large S2-S1 energy gaps might exhibit upper state fluorescence. Photodecomposition quantum yields of a series of sterically hindered p-aminobenzene diazonium cations in water were found structurally and wavelength dependent and unquenched in aqueous sodium bromide solutions. Photodecomposition of diazonium materials did not produce a metastable species with a longer lifetime than 1 msec.

Evleth, E. M.↗
NASA NTRS1975

Syntheses and degradations of fluorinated heterocyclics

The relative stability of two ring systems, the triazine rings and 1,2,4-oxadiazoles, which offer potential crosslinks useful for curing perfluoroalkyl ether elastomers, has been investigated. Tris (perfluoro-n-heptyl)-s-triazine, the perfluoroether substituted-s-triazine, 1,4-bis/(5-perfluoro-n-heptyl)-1,2,4-oxadiazolyl/benzene, its perfluoroalkyl ether substituted analog, and 3,5-bis-(perfluoro-n-heptyl)-1,2,4-oxadiazole were synthesized and subjected to thermal and oxidative degradation at 235 and 325 C and to hydrolytic degradation at 235 C. The perfluoroalkyl ether substituted triazine and 3,5-bis(perfluoro-n-heptyl)-1,2,4-oxadiazole were found to be stable under all conditions investigated.

Paciorek, K. L.↗
NASA NTRS1979

Preparation of heterocyclic block copolymer from perfluoroalkylene oxide alpha, omega-diamidoximes

Diamidoxime monomers are intermolecularly and thermally condensed to form a heat and chemical resistant polymer containing 1,2,4-oxadiazole linkages with identical bivalent organic radicals or any combination of bivalent organic radicals selected from the group consisting of -(CX(sub 2))p-, wherein P ranges from 2 to 8 when X is fluorine and 2 to 18 when X is hydrogen, chlorine, nitro or aryl; arylene; and an oligometric or polymeric radical prepared by reacting a dicarboxylic acid halide with a fluorinated epoxide and having the formula: (CFY(OCF(sub 2)CFY)sub m)O(CX(sub 2))(sub p)O(CFYCF(sub 2)O)(sub n)CFY wherein Y is flourine or tryifluoromethyl, X is nitro, aryl, hydrogen, chlorine or fluorine, preferably the latter, p ranges from 1 to 18 and m+n ranges from 2 to 7.

Ross, L. O.↗