94 research outputs found
Improving selectivity in catalytic hydrodefluorination by limiting SNV reactivity
Catalytic hydrodefluorination of perfluoroallylbenzene with Cp2TiH in THF is
unselective and yields a variety of previously unknown compounds,
predominantly activated in the allylic position. Several different mechanisms
have been examined in detail using solvent corrected (THF) DFT(M06-2X)
calculations for the archetypal perfluorinated olefin perfluoropropene and
perfluoroallylbenzene: (a) single electron transfer, (b)
hydrometallation/fluoride elimination, (c) Ď-bond metathesis (allylic or
vinylic), and (d) nucleophilic vinylic substitution (SNV, w/o TiâF contacts in
the TS). SNV is shown to be a competitive mechanism to hydrometallation and
proceeds via ionic species from which F-elimination is facile and unselective
leading to low selectivity in polar solvents. Subsequent experiments show that
selectivity can be increased in a non-polar solvent
Crystal structure of 4,4-dimethyl-2-(trifluoromethyl)-4,5-dihydro-1H-imidazole, C6H9F3N2
C6H9F3N2, monoclinic, P21/n (no. 14), a = 10.6224(9) Ă
, b = 11.8639(9) Ă
, c = 13.3139(11) Ă
, β = 105.903(3)°, V = 1613.6(2) Ă
3, Z = 8, Rgt(F) = 0.0618, wRref(F2) = 0.1629, T = 102(2) K [1â3]
Sumanenylferrocenes and their solid state self-assembly
The first ferrocene-fused organometallic compounds derived from the buckybowl
sumanene (C21H12) are presented. Both compounds, sumanenylferrocene and
1,1â˛-disumanenylferrocene, have been synthesized by Negishi-type cross-
coupling of iodosumanene and were studied crystallographically.
Sumanenylferrocenes form unique packing motifs, which are both different from
those of their corannulene congeners and sumanene itself
Straightforward approach to efficient oxidative DNA cleaving agents based on Cu(II) complexes of heterosubstituted cyclens
The Cu(II) complexes of cyclen and two of its heterosubstituted analogues were
shown to be efficient oxidative DNA cleavers. The reactivity strongly depends
on the heteroatom inserted into the macrocycle (O > S > N)
Functional polyoxometalates from solvothermal reactions of VOSO4 with tripodal alkoxides â a study on the reactivity of different âtrisâ derivatives
We report a study on the structure directing effects of functional groups and
counterions. The aim was to find a facile and high yielding synthetic
procedure to obtain polyoxometalate (POM) building blocks for post-
functionalisation. Therefore, solvothermal reactions of VOSO4 with various
tris(hydroxymethyl)methane derivatives in alkaline methanolic solutions were
investigated. In doing so, new POM fragments were isolated and characterised.
The binding modes of the functionalised tripodal alkoxides turned out to be
surprisingly different
Cycloaddition Reactions of the Diphosphenyl Complex (Ρ5-C5Me5)(CO)2Fe-P=P-Mes* (Mes* = 2,4,6-tBu3C6H2) with Hexafluoroacetone. X-Ray Structure Analyses of (Ρ5-C5Me5)(CO) Fe P(=PMes*)OC(CF3)2CO and (Ρ5-C5Me5)(CO)2FePP(Mes*)OC(CF3)2
Weber L, Buchwald S, Lentz D, Preugschat D, Stammler H-G, Neumann B. Cycloaddition Reactions of the Diphosphenyl Complex (Ρ5-C5Me5)(CO)2Fe-P=P-Mes* (Mes* = 2,4,6-tBu3C6H2) with Hexafluoroacetone. X-Ray Structure Analyses of (Ρ5-C5Me5)(CO) Fe P(=PMes*)OC(CF3)2CO and (Ρ5-C5Me5)(CO)2FePP(Mes*)OC(CF3)2. Organometallics. 1992;11(7):2351-2353.The diphosphenyl complex (eta-5-C5Me5)-(CO)2Fe-P=P-Mes* (Mes* = 2,4,6-tBu3C6H2) undergoes a [3 + 2] dipolar cycloaddition with hexafluoroacetone to give the metalla heterocycle (eta-5-C5Me5)(CO)-Fe-P(=PMes*)OC(CF3)2C(O) with a remarkably short Fe-P bond (2.084 (4) angstrom) and an exocyclic P=P bond. When stored in solution at -40-degrees-C, this complex partly rearranges to the metalated 1-oxa-2,3-diphosphetane (eta-5-C5Me5)(CO)2Fe-P-P(Mes*)OC(CF3)2. The molecular structures of both isomers were elucidated by single-crystal X-ray analyses
Synthesis, XRD and HS-Analysis
An efficient microwave-assisted one-step synthetic route toward Mannich bases is developed from 4-hydroxyacetophenone and different secondary amines in quantitative yields, via a regioselective substitution reaction. The reaction takes a short time and is non-catalyzed and reproducible on a gram scale. The environmentally benign methodology provides a novel alternative, to the conventional methodologies, for the synthesis of mono- and disubstituted Mannich bases of 4-hydroxyacetophenone. All compounds were well-characterized by FT-IR, 1H NMR, 13C NMR, and mass spectrometry. The structures of 1-{4-hydroxy-3-[(morpholin-4-yl)methyl]phenyl}ethan-1-one (2a) and 1-{4-hydroxy-3-[(pyrrolidin-1-yl)methyl]phenyl}ethan-1-one (3a) were determined by single crystal X-ray crystallography. Compound 2a and 3a crystallize in monoclinic, P21/n, and orthorhombic, Pbca, respectively. The most characteristic features of the molecular structure of 2a is that the morpholine fragment adopts a chair conformation with strong intramolecular hydrogen bonding. Compound 3a exhibits intermolecular hydrogen bonding, too. Furthermore, the computed Hirshfeld surface analysis confirms H-bonds and ĎâĎ stack interactions obtained by XRD packing analyses
Catching Element Formation In The Act
Gamma-ray astronomy explores the most energetic photons in nature to address
some of the most pressing puzzles in contemporary astrophysics. It encompasses
a wide range of objects and phenomena: stars, supernovae, novae, neutron stars,
stellar-mass black holes, nucleosynthesis, the interstellar medium, cosmic rays
and relativistic-particle acceleration, and the evolution of galaxies. MeV
gamma-rays provide a unique probe of nuclear processes in astronomy, directly
measuring radioactive decay, nuclear de-excitation, and positron annihilation.
The substantial information carried by gamma-ray photons allows us to see
deeper into these objects, the bulk of the power is often emitted at gamma-ray
energies, and radioactivity provides a natural physical clock that adds unique
information. New science will be driven by time-domain population studies at
gamma-ray energies. This science is enabled by next-generation gamma-ray
instruments with one to two orders of magnitude better sensitivity, larger sky
coverage, and faster cadence than all previous gamma-ray instruments. This
transformative capability permits: (a) the accurate identification of the
gamma-ray emitting objects and correlations with observations taken at other
wavelengths and with other messengers; (b) construction of new gamma-ray maps
of the Milky Way and other nearby galaxies where extended regions are
distinguished from point sources; and (c) considerable serendipitous science of
scarce events -- nearby neutron star mergers, for example. Advances in
technology push the performance of new gamma-ray instruments to address a wide
set of astrophysical questions.Comment: 14 pages including 3 figure
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