Search results for "redox chemistry"
showing 10 items of 11 documents
Enantiomerically pure trinuclear helicates via diastereoselective self-assembly and characterization of their redox chemistry.
2014
A tris(bipyridine) ligand 1 with two BINOL (BINOL = 2, 2′-dihydroxy-1, 1′-binaphthyl) groups has been prepared in two enantiomerically pure forms. This ligand undergoes completely diastereoselective self-assembly into D2-symmeteric double-stranded trinuclear helicates upon coordination to copper(I) and silver(I) ions and to D3-symmetric triple-stranded trinuclear helicates upon coordination to copper(II), zinc(II), and iron(II) ions as demonstrated by mass spectrometry, NMR and CD spectroscopy in combination with quantum chemical calculations and X-ray diffraction analysis. According to the calculations, the single diastereomers that are formed during the self-assembly process are strongly …
Are agricultural soils under a continental temperate climate susceptible to episodic reducing conditions and increased leaching of phosphorus?
2012
International audience; Soil science research has probably underestimated the significance that short-term, episodic cycles of reduction and oxidation has had on phosphorus (P) reactivity. Here, the effects of eleven pulsed reduction-oxidation (including wet-dry) cycles on soil P dynamics are compared for 12 soils having contrasting properties and all overfertilised with respect to P. The laboratory based incubation conditions attempted to simulate transient waterlogging of the soil profile and involved repeated sampling and analysis of both the solution and solid phase P forms. An initial increase in P concentration in solution that occurred up to and including the fourth full cycle was fo…
Luminescence and Light‐Driven Energy and Electron Transfer from an Exceptionally Long‐Lived Excited State of a Non‐Innocent Chromium(III) Complex
2019
Abstract Photoactive metal complexes employing Earth‐abundant metal ions are a key to sustainable photophysical and photochemical applications. We exploit the effects of an inversion center and ligand non‐innocence to tune the luminescence and photochemistry of the excited state of the [CrN6] chromophore [Cr(tpe)2]3+ with close to octahedral symmetry (tpe=1,1,1‐tris(pyrid‐2‐yl)ethane). [Cr(tpe)2]3+ exhibits the longest luminescence lifetime (τ=4500 μs) reported up to date for a molecular polypyridyl chromium(III) complex together with a very high luminescence quantum yield of Φ=8.2 % at room temperature in fluid solution. Furthermore, the tpe ligands in [Cr(tpe)2]3+ are redox non‐innocent, …
Enhanced electron-transfer properties of cofacial porphyrin dimers through pi-pi interactions
2009
pi-pi assisted: Photoinduced electron transfer from cofacial porphyrin dimers to electron acceptors is prominently accelerated, whereas the back electron transfer is decelerated, relative to the corresponding porphyrin monomer (see figure).The radical cation of zinc tetrapentylporphyrin is dimerized with an excess of the neutral counterpart to form the dimer radical cation in which the unpaired electron is delocalized over both porphyrin rings. The dimeric radical cation exhibits an NIR absorption spectrum characteristic of weak pi-bond formation between the porphyrin rings. When cofacial porphyrin dimers, linked by different spacers, are oxidized such pi-bond formation between the porphyri…
A Square-Planar Dinickel(II) Complex with a Noninnocent Dinucleating Oxamate Ligand: Evidence for a Ligand Radical Species
1999
[EN] The new bimetallic nickel(II) compound (PPh4)4[Ni2(2)]·6H2O (3), where H8[2] stands for N,N',N'',N'''-1,2,4,5-benzene-tetrayltetrakis(oxamic acid), has been synthesized and its crystal structure determined by single-crystal X-ray diffraction. The structure of 3 consists of [Ni2(n4:n4-2)]4- anions, tetraphenylphosphonium cations, and water molecules. Facile one-electron oxidation of the square-planar diamagnetic dinickel(II) complex [Ni2(n4:n4-2)]4- generates the metallo-radical species [Ni2(n4:n4-2·+)]3- with characteristic intra-ligand ¿cation radical transitions in the visible region (475-550 nm) as well as a typical quasi-isotropic EPR signal at g ¿ 2.0.
Thermodynamic and electrochemical study of tailor-made crown ethers for redox-switchable (pseudo)rotaxanes
2020
Crown ethers are common building blocks in supramolecular chemistry and are frequently applied as cation sensors or as subunits in synthetic molecular machines. Developing switchable and specifically designed crown ethers enables the implementation of function into molecular assemblies. Seven tailor-made redox-active crown ethers incorporating tetrathiafulvalene (TTF) or naphthalene diimide (NDI) as redox-switchable building blocks are described with regard to their potential to form redox-switchable rotaxanes. A combination of isothermal titration calorimetry and voltammetric techniques reveals correlations between the binding energies and redox-switching properties of the corresponding ps…
Planar-Chiral 1,1 '-Diboryl Metallocenes: Diastereoselective Synthesis from Boryl Cyclopentadienides and Spin Density Analysis of a Diborylcobaltocene
2017
International audience; The reaction of nonsubstituted alkali metal cyclopentadienides with haloboranes leads to similar to 90:10 mixtures of isomeric diene products that can be deprotonated to give simple boryl cyclopentadienides. We extended this transformation to the sterically hindered lithium tert-butylcyclopentadienide 1 using FBMe(s)2 (Mes = 2,4,6-trimethylphenyl) and ClBCy2 as electrophiles. The boryl group is selectively introduced in the remote position to minimize steric congestion. The new boryl dienes are obtained as mixtures of isomers, and subsequent deprotonation with MeLi or LiHMDS affords the lithium 1,3-disubstituted cyclopentadienides Sa,b in yields over 95%. Direct asse…
Ferrocenyl-Labeled Sugar Amino Acids: Conformation and Properties
2012
Novel organometallic sugar amino acid conjugates 1–5 have been prepared by amide coupling of O-protected N-acetylmuramic acid and iso-muramic acid (2-[3-amino-2, 5-dihydroxy-6-(hydroxymethyl)oxan-4-yl]oxypropanoic acid) with 1-aminoferrocene, 1-aminoferrocene-1′-carboxylic acid (H-Fca-OH), or 1, 1′-diaminoferrocene, respectively. The influence of the ferrocenyl moiety and presence of additional remote potential hydrogen atom acceptors and donors at the ferrocenyl core on the conformation and lipophilicity is investigated by TLC, IR, NMR, and CD spectroscopic methods augmented by density functional calculations. Furthermore, the redox potential of the ferrocene/ferrocenium couple is tuned by…
Gold Redox Catalytic Cycles for the Oxidative Coupling of Alkynes
2011
[EN] Au(I)/Au(III) catalytic cycles are catalytically competent to perform the oxidative coupling of alkynes in the homogeneous phase at room temperature and without any protecting atmosphere. Selectfluor as oxidant, wet acetonitrile as solvent, and sodium carbonate as base are the reagents of choice. Both aromatic and alkyl alkynes can be coupled, and mechanistic studies reveal that at least two gold species having different oxidation states are implicated in the key step of the coupling.
Bond Stretching and Redox Behavior in Coinage Metal Complexes of the Dichalcogenide Dianions [(SPh2P)2CEEC(PPh2S)2]2− (E=S, Se): Diradical Character …
2011
The metathetical reactions of a) [Li(tmeda)]2[(S)C(PPh2S)2] (Li2⋅3 c) with CuCl2 and b) [Li(tmeda)]2[(SPh2P)2CSSC(PPh2S)2] (Li2⋅4 c) with two equivalents of CuCl both afford the binuclear CuI complex {Cu2[(SPh2P)2CSSC(PPh2S)2]} (5 c). The elongated (C)S[BOND]S(C) bond (ca. 2.54 and 2.72 Å) of the dianionic ligand observed in the solid-state structure of 5 c indicate the presence of diradical character as supported by theoretical analyses. The treatment of [Li(tmeda)]2[(SPh2P)2CSeSeC(PPh2S)2] (Li2⋅4 b) and Li2⋅4 c with AgOSO2CF3 produce the analogous AgI derivatives, {Ag2[(SPh2P)2CEEC(PPh2S)2]} (6 b, E=Se; 6 c, E=S), respectively. The diselenide complex 6 b exhibits notably weaker Ag[BOND]Se…