scholarly journals One- and Two-Electron Reduction of Triarylborane-Based Helical Donor-Acceptor Compounds

2021 ◽  
Author(s):  
Xiangqing Jia ◽  
Jörn Nitsch ◽  
Zhu Wu ◽  
Alexandra Friedrich ◽  
Johannes Krebs ◽  
...  
Keyword(s):  
Chemical Reduction ◽  
Helix 12 ◽  
Donor Acceptor ◽  
Electron Reduction

One-electron chemical reduction of 10-(dimesitylboryl)-N,N-di-p-tolylbenzo[c]phenanthrene-4-amine (3-B(Mes)2-[4]helix-9-N(p-Tol)2) 1 and 13-(dimesitylboryl)-N,N-di-p-tolyldibenzo[c,g]phenanthrene-8-amine (3-B(Mes)2-[5]helix-12-N(p-Tol)2) 2 gives rise to monoanions with extensive delocalization over the annulated helicene rings and the boron pz orbital. Two-electron chemical...

Room Temperature Alkali Metal Reduction of Carbon Dioxide

2020 ◽  
Author(s):  
Lucas A. Freeman ◽  
Akachukwu D. Obi ◽  
Haleigh R. Machost ◽  
Andrew Molino ◽  
Asa W. Nichols ◽  
...  
Keyword(s):  
Alkali Metal ◽  
Alkali Metals ◽  
Room Temperature ◽  
Chemical Reduction ◽  
Bond Cleavage ◽  
Open Shell ◽  
Metal Reduction ◽  
One Pot ◽  
Earth Abundant ◽  
Electron Reduction

The reduction of the relatively inert carbon–oxygen bonds of CO<sub>2</sub> to access useful CO<sub>2</sub>-derived organic products is one of the most important fundamental challenges in synthetic chemistry. Facilitating this bond-cleavage using earth-abundant, non-toxic main group elements (MGEs) is especially arduous because of the difficulty in achieving strong inner-sphere interactions between CO<sub>2</sub> and the MGE. Herein we report the first successful chemical reduction of CO<sub>2</sub> at room temperature by alkali metals, promoted by a cyclic(alkyl)(amino) carbene (CAAC). One-electron reduction of CAAC-CO<sub>2</sub> adduct (<b>1</b>) with lithium, sodium or potassium metal yields stable monoanionic radicals clusters [M(CAAC–CO<sub>2</sub>)]<sub>n</sub>(M = Li, Na, K, <b> 2</b>-<b>4</b>) and two-electron alkali metal reduction affords open-shell, dianionic clusters of the general formula [M<sub>2</sub>(CAAC–CO<sub>2</sub>)]<sub>n </sub>(<b>5</b>-<b>8</b>). It is notable that these crystalline clusters of reduced CO<sub>2</sub> may also be isolated via the “one-pot” reaction of free CO<sub>2</sub> with free CAAC followed by the addition of alkali metals – a reductive process which does not occur in the absence of carbene. Each of the products <b>2</b>-<b>8</b> were investigated using a combination of experimental and theoretical methods.<br>

Electronic Couplings in the Reduced State Lie at the Origin of Color Changes of Ommochromes

2020 ◽  
Author(s):  
Florent Figon ◽  
Jérôme Casas ◽  
Ilaria Ciofini ◽  
Carlo Adamo
Keyword(s):  
Density Functional ◽  
Chemical Reduction ◽  
Functional Theory ◽  
Color Changes ◽  
Vis Spectroscopy ◽  
Rational Explanation ◽  
Photophysical Behavior ◽  
Electron Reduction ◽  
The Many ◽  
Reduced State

In the colorful world of pigments and dyes, the chemical reduction of chromophores usually leads to bleaching because of π-conjugation interruption. Yet, the natural phenoxazinone-based ommochrome pigment called xanthommatin displays a bathochromic (i.e. red) shift upon two-electron reduction to its corresponding phenoxazine, whose electronic origins are not completely disclosed. In this study, we investigated, at quantum chemical level, a series of phenoxazinone/phenoxazine pairs that was previously explored by UV-Vis spectroscopy (Schäfer and Geyer, 1972), and which displays different hypsochromic and bathochromic shifts upon reduction. Density Functional Theory (DFT) and Time-Dependent DFT (TDDFT) have been applied to compute their optical properties in order to find a rational explanation of the observed photophysical behavior. Based on our results, we propose that the electro-accepting power of auxochromes and their conjugation facilitate intramolecular charge-transfers across the phenoxazine bridge by lowering unoccupied molecular orbitals via electronic and geometric couplings, leading ultimately to bathochromy. Our findings therefore suggest new potential ways to adjust the color-changing ability of phenoxazinones in technological contexts. Overall, this model extends our mechanistic understanding of the many biological functions of ommochromes in invertebrates, from tunable color changes to antiradical behaviors.<br>

Electronic Couplings in the Reduced State Lie at the Origin of Color Changes of Ommochromes

2020 ◽  
Author(s):  
Florent Figon ◽  
Jérôme Casas ◽  
Ilaria Ciofini ◽  
Carlo Adamo
Keyword(s):  
Density Functional ◽  
Chemical Reduction ◽  
Functional Theory ◽  
Color Changes ◽  
Vis Spectroscopy ◽  
Rational Explanation ◽  
Photophysical Behavior ◽  
Electron Reduction ◽  
The Many ◽  
Reduced State

In the colorful world of pigments and dyes, the chemical reduction of chromophores usually leads to bleaching because of π-conjugation interruption. Yet, the natural phenoxazinone-based ommochrome pigment called xanthommatin displays a bathochromic (i.e. red) shift upon two-electron reduction to its corresponding phenoxazine, whose electronic origins are not completely disclosed. In this study, we investigated, at quantum chemical level, a series of phenoxazinone/phenoxazine pairs that was previously explored by UV-Vis spectroscopy (Schäfer and Geyer, 1972), and which displays different hypsochromic and bathochromic shifts upon reduction. Density Functional Theory (DFT) and Time-Dependent DFT (TDDFT) have been applied to compute their optical properties in order to find a rational explanation of the observed photophysical behavior. Based on our results, we propose that the electro-accepting power of auxochromes and their conjugation facilitate intramolecular charge-transfers across the phenoxazine bridge by lowering unoccupied molecular orbitals via electronic and geometric couplings, leading ultimately to bathochromy. Our findings therefore suggest new potential ways to adjust the color-changing ability of phenoxazinones in technological contexts. Overall, this model extends our mechanistic understanding of the many biological functions of ommochromes in invertebrates, from tunable color changes to antiradical behaviors.<br>

Resonance Raman and absorption properties of Zn(II) and Ni(II) polynitroporphyrins and their chemical reduction products

2007 ◽  
Vol 11 (09) ◽  
pp. 682-690 ◽  
Author(s):  
Sergei N. Terekhov ◽  
Gennadii N. Sinyakov ◽  
Evgeni E. Lobko ◽  
Pierrette Battiony ◽  
Pierre-Yves Turpin ◽  
...  
Keyword(s):  
Steady State ◽  
Chemical Reduction ◽  
Resonance Raman ◽  
Absorption Properties ◽  
Aryl Ring ◽  
Electron Reduction ◽  
The One ◽  
Steady State Absorption ◽  
Excited Resonance ◽  
Anion Radicals

Electron-deficient metallocomplexes of dodeca- and octanitroporphyrins produced by the introduction of 8 β-nitro substituents or 8 β-nitro and a meta-nitro substituent on each meso-aryl ring of Zn (II) and Ni (II) [meso-tetra-(2,6-dichlorophenyl)porphyrin] (Zn8, Ni8 and Zn12, Ni12, respectively) and their air-stable reduced species have been characterized by steady-state absorption and Soret-excited resonance Raman spectroscopies. One-electron reduced species of the metallocomplexes were produced by three different procedures (in deprotonated tetrahydrofuran in air ambient, in tetralhydrofuran with the addition of piperidine in air ambient, and in contact with a sodium mirror under vacuum) and demonstrated similar absorption and RR spectra. It is concluded on the basis of the RR spectra that the one-electron reduction products of the studied polynitrosubstituted metalloporphyrins are π–anion radicals in character.

Towards supported catalyst models: the synthesis, characterization, redox chemistry, and structures of the complexes Ti(OAr′)4 (Ar′ = C6H4(2-t-Bu), C6H(2,3,5,6-Me)4)

1991 ◽  
Vol 69 (1) ◽  
pp. 172-178 ◽  
Author(s):  
Robert T. Toth ◽  
Douglas W. Stephan
Keyword(s):  
Chemical Reduction ◽  
Supported Catalyst ◽  
Redox Chemistry ◽  
Orthorhombic Space Group ◽  
Cyclic Voltammetric ◽  
Space Group ◽  
Electron Reduction ◽  
Catalyst Systems ◽  
Ligand Transfer ◽  
Early Late

Reaction of substituted phenoxides with TiCl4 affords the species Ti(OAr′)4 (Ar′ = C6H4(2-t-Bu), 1; Ar′ = C6H(2,3,5,6-Me)4, 2). The compound Ti(OC6H4(2-t-Bu))4, 1, crystallizes in the tetragonal space group [Formula: see text], with a = 15.203(4) Å, c = 8.026(3) Å, Z = 2, and V = 1855(2) Å3. The compound Ti(OC6H(2,3,5,6-Me)4)4, 2, crystallizes in the orthorhombic space group Pbcn, with a = 16.539(7) Å, b = 16.136(6) Å, c = 27.716(12) Å, Z = 8, and V = 7397(9) Å3. The geometry of the Ti coordination sphere in these complexes is best described as pseudo-tetrahedral. In the case of 1 strict crystallographic [Formula: see text] symmetry is imposed. The complex 2 exhibits reversible cyclic voltammetric behaviour consistent with a one electron reduction to the Ti(III) analogue. Chemical reduction of 2 employing sodium amalgam affords the quantitative formation of (C6H(2,3,5,6-Me)4O)2Ti(μ-OC6H(2,3,5,6-Me)4)2Na(THF)2, 3. The reaction of 3 with [(COD)Rh(μ-Cl)]2 does not afford the Ti(III)/Rh(I) early–late heterobimetallic (ELHB) complex (C6H(2,3,5,6-Me)4O)2Ti(μ-OC6H(2,3,5,6-Me)4)2Rh(COD). The nature of all products is not known; however, redox chemistry, in which electron transfer from Ti(III) to Rh(I) occurs is evidenced by the generation of 2 and Rh(0). In addition, ligand transfer reactions giving uncharacterized Rh-alkoxides are suggested by the spectral data. The implications and ramifications for the synthesis of alkoxide bridged ELHB models of bimetallic heterogeneous catalyst systems are discussed. Key words: titanium phenoxides, redox chemistry, structures.

4,5-Dihydro-4,5-dihydroxyimidazoles as products of the reduction of 2-nitroimidazoles. HPLC assay and demonstration of equilibrium transfer of glyoxal to guanine

1989 ◽  
Vol 67 (12) ◽  
pp. 2128-2135 ◽  
Author(s):  
Rick Panicucci ◽  
Robert A. McClelland
Keyword(s):  
Electrochemical Reduction ◽  
Hplc Analysis ◽  
Chemical Reduction ◽  
Authentic Sample ◽  
Hplc Method ◽  
Radiation Chemical ◽  
Mercury Cathode ◽  
Guanine Derivatives ◽  
Electron Reduction ◽  
Quantitative Hplc Analysis

An HPLC method has been employed to study the electrochemical reduction (mercury cathode at −800 mV with respect to calomel electrode) of the 2-nitroimidazole benznidazole (N′-benzyl-(2′-nitro-1′-imidazoyl)acetamide). The principal product of this reduction is the cyclic guanidinium ion 3c (protonated N′-benzyl-(2′-amino-4′,5′-dihydro-4′,5′-dihydroxy-1-imidazoyl)acetamide), which forms in a linear fashion as the nitroimidazole is reduced and accounts for 75% of the product upon completion of the reduction. To perform the HPLC analysis quantitatively an authentic sample of this product (isolated as cis-trans isomers) was prepared as the sulfate salt through the reaction of N-benzyl-2-guanidinoacetamide sulfate with aqueous glyoxal. The two isomers of 3c arise through the nonreductive decomposition of the 2-hydroxylaminoimidazole, which is the product of a four-electron reduction of the nitroimidazole. Analysis of high field 1H NMR spectra also showed that the two isomers of 3c were the principal products following electrochemical reduction, neutral aqueous zinc reduction, and radiation chemical reduction. Previous investigations using NMR of the reductions of misonidazole (3-methoxy-1-(2′-nitro-1′-imidazoyl)-2-propanol) and 1-methyl-2-nitroimidazole have shown that the corresponding dihydroimidazoles 3a and 3b are the major products. The agreement of these various NMR and HPLC results suggests that the formation of dihydroimidazoles 3 is a general phenomenon for model reductions of 2-nitroimidazoles in neutral aqueous solution. Previous workers have shown that 2-nitroimidazole reduction mixtures, when treated with guanine derivatives, form the adduct 4 derived from the guanine and glyoxal. This work demonstrates that this adduct is also formed when authentic samples of 3a, 3b, and 3c are reacted with 2′-deoxyguanosine. A quantitative HPLC analysis, however, demonstrates that the reaction does not proceed to completion, and in fact the equilibrium for formation of 4 is unfavorable. This suggests that guanines are not useful derivatizing agents for the quantitative assay of "glyoxal-like" products formed in chemical or biological reductions of 2-nitroimidazoles. Keywords: nitroimidazole, reduction of nitroimidazoles, glyoxal from nitroimidazoles.

Room Temperature Alkali Metal Reduction of Carbon Dioxide

2020 ◽  
Author(s):  
Lucas A. Freeman ◽  
Akachukwu D. Obi ◽  
Haleigh R. Machost ◽  
Andrew Molino ◽  
Asa W. Nichols ◽  
...  
Keyword(s):  
Alkali Metal ◽  
Alkali Metals ◽  
Room Temperature ◽  
Chemical Reduction ◽  
Bond Cleavage ◽  
Open Shell ◽  
Metal Reduction ◽  
One Pot ◽  
Earth Abundant ◽  
Electron Reduction

The reduction of the relatively inert carbon–oxygen bonds of CO<sub>2</sub> to access useful CO<sub>2</sub>-derived organic products is one of the most important fundamental challenges in synthetic chemistry. Facilitating this bond-cleavage using earth-abundant, non-toxic main group elements (MGEs) is especially arduous because of the difficulty in achieving strong inner-sphere interactions between CO<sub>2</sub> and the MGE. Herein we report the first successful chemical reduction of CO<sub>2</sub> at room temperature by alkali metals, promoted by a cyclic(alkyl)(amino) carbene (CAAC). One-electron reduction of CAAC-CO<sub>2</sub> adduct (<b>1</b>) with lithium, sodium or potassium metal yields stable monoanionic radicals clusters [M(CAAC–CO<sub>2</sub>)]<sub>n</sub>(M = Li, Na, K, <b> 2</b>-<b>4</b>) and two-electron alkali metal reduction affords open-shell, dianionic clusters of the general formula [M<sub>2</sub>(CAAC–CO<sub>2</sub>)]<sub>n </sub>(<b>5</b>-<b>8</b>). It is notable that these crystalline clusters of reduced CO<sub>2</sub> may also be isolated via the “one-pot” reaction of free CO<sub>2</sub> with free CAAC followed by the addition of alkali metals – a reductive process which does not occur in the absence of carbene. Each of the products <b>2</b>-<b>8</b> were investigated using a combination of experimental and theoretical methods.<br>

EPR spectroscopy study of di-o-quinone bridged by π-extended TTF: redox behavior and binding modes as a ligand

2016 ◽  
Vol 40 (2) ◽  
pp. 1244-1249 ◽  
Author(s):  
Nikolay O. Chalkov ◽  
Vladimir K. Cherkasov ◽  
Gleb A. Abakumov ◽  
Andrey G. Starikov ◽  
Viacheslav A. Kuropatov
Keyword(s):  
Epr Spectroscopy ◽  
Chemical Reduction ◽  
Redox Behavior ◽  
Binding Modes ◽  
Spectroscopy Study ◽  
Donor Acceptor

Chemical reduction of an acceptor–donor–acceptor bis-chelating system: an EPR and UV-vis study.

One-Step Synthesis and Magnetic Phase Transformation of Ln-TM-B Alloy by Chemical Reduction

2007 ◽  
Vol 0 (0) ◽  
pp. 0-0
Author(s):  
C.W. Kim ◽  
Y.H. Kim ◽  
H.G. Cha ◽  
D.K. Lee ◽  
Y.S. Kang
Keyword(s):  
Phase Transformation ◽  
Magnetic Phase ◽  
Chemical Reduction ◽  
One Step
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