Search results for "ROC"
showing 10 items of 37446 documents
Cathodic Corrosion of Metal Electrodes—How to Prevent It in Electroorganic Synthesis
2021
The critical aspects of the corrosion of metal electrodes in cathodic reductions are covered. We discuss the involved mechanisms including alloying with alkali metals, cathodic etching in aqueous and aprotic media, and formation of metal hydrides and organometallics. Successful approaches that have been implemented to suppress cathodic corrosion are reviewed. We present several examples from electroorganic synthesis where the clever use of alloys instead of soft neat heavy metals and the application of protective cationic additives have allowed to successfully exploit these materials as cathodes. Because of the high overpotential for the hydrogen evolution reaction, such cathodes can contri…
Total Synthesis of (-)-Oxycodone via Anodic Aryl-Aryl Coupling.
2019
A fully regio- and diastereoselective electrochemical 4a–2′-coupling of a 3′,4′,5′-trioxygenated laudanosine derivative enables the synthesis of the corresponding morphinandienone. This key intermediate is further transformed into (−)-oxycodone through conjugate nucleophilic substitution for E-ring closure and [4 + 2] cycloaddition with photogenerated singlet oxygen to accomplish diastereoselective hydroxylation at C-14. The anodic transformation provides high yields and can be performed under constant current conditions both in a simple undivided cell or in continuous flow.
Electrochemical and spectroscopic studies of poly(diethoxyphosphoryl)porphyrins
2011
Abstract The synthesis and electrochemical characterization of two related series of porphyrins bearing diethoxyphosphoryl groups are reported. One group of compounds is represented as (T( p -R)PP)M where R = phos = P(O)(OEt) 2 and M = Zn(II) or H 2 while the other is represented as (di( p -R)Pdi(phos)P)M where R = P(O)(OEt) 2 , H or CH 3 and M = Zn(II) or H 2 . Each porphyrin was investigated by electrochemistry and thin-layer spectroelectrochemistry in CH 2 Cl 2 , CDCl 3 , CHCl 3 or PhCN containing tetra- n -butylammonium perchlorate (TBAP) as supporting electrolyte. The highly electron-withdrawing P(O)(OEt) 2 groups lead to easier reductions and harder oxidations than the two comparison …
Molecular materials based upon organic π-donors and magnetic anions
2000
Electrochemical combination of the magnetic dinuclear anion [MM'(C 2 O 4 )(NCS) 8 ] 4- (MM' = CrCr, CrFe) or paramagnetic mononuclear anion [Cr(NCS) 6 ] 3- with the ET organic π-donor (ET = BEDT-TTF = bis(ethylenedithio)tetrathiafulvalene) gives rise to two new series of molecular hybrid salts formulated (ET) 5 [MM'(C 2 O 4 )(NCS) 8 (MM' = CrCr (1), CrFe (2)), (ET) 8 [MM'(C 2 O 4 )(NCS) 8 ] (3), (ET) 5.5 f Cr(NCS) 6 ] (4) and (ET) 5 [(C 2 H 5 ) 4 N] [Cr(NCS) 6 ](THF) (5) (THF = tetrahydrofuran). The crystal structures consist of alternating organic and inorganic layers. The organic part does not produce any detectable effect on the magnetic properties coming from the inorganic sublattice. T…
Solution, structural and photophysical aspects of substituent effects in the N^N ligand in [Ir(C^N)2(N^N)]+ complexes
2013
The syntheses and properties of a series of eleven new [Ir(ppy)2(N^N)][PF6] complexes (Hppy = 2-phenylpyridine) are reported. The N^N ligands are based on 2,2-bipyridine (bpy), substituted in the 6- or 5-positions with groups that are structurally and electronically diverse. All but two of the N^N ligands incorporate an aromatic ring, designed to facilitate intra-cation face-to-face π-interactions between the N^N and one [ppy](-) ligand. Within the set of ligands, 6-(3-tolyl)-2,2'-bipyridine (5), 4,6-bis(4-nitrophenyl)-2,2'-bipyridine (9), and 4,6-bis(3,4,5-trimethoxyphenyl)-2,2'-bipyridine (10) are new and their characterization includes single crystal structures of 9, and two polymorphs o…
Controlling the Host-Guest Interaction Mode through a Redox Stimulus
2017
International audience; A proof-of-concept related to the redox-control of the binding/releasing process in a host-guest system is achieved by designing a neutral and robust Pt-based redox-active metallacage involving two extended-tetrathiafulvalene (exTTF) ligands. When neutral, the cage is able to bind a planar polyaromatic guest (coronene). Remarkably, the chemical or electrochemical oxidation of the host-guest complex leads to the reversible expulsion of the guest outside the cavity, which is assigned to a drastic change of the host-guest interaction mode, illustrating the key role of counteranions along the exchange process. The reversible process is supported by various experimental d…
Long-range electronic connection in picket-fence like ferrocene–porphyrin derivatives
2012
The effects of a direct connection between ferrocene and porphyrin units have been thoroughly investigated by electrochemical and spectroscopic methods. These data not only reveal that substitution of the porphyrin macrocycle by one, two, three or four ferrocenyl groups strongly affects the electronic properties of the porphyrin and ferrocenyl moieties, they also clearly demonstrate that the metallocene centres are "connected" through the porphyrin-based electronic network. The dynamic properties of selected ferrocene-porphyrin conjugates have been investigated by VT NMR and metadynamic calculations. 1,3-Dithiolanyl protecting groups have been introduced on the upper rings of the ferrocene …
Catalytic activity of biscobalt porphyrin-corrole dyads toward the reduction of dioxygen
2009
A series of biscobalt cofacial porphyrin-corrole dyads bearing mesityl substituents at the meso positions of the corrole ring were investigated as to their electrochemistry, spectroelectrochemistry, and CO binding properties in nonaqueous media and then applied to the surface of a graphite electrode and tested as electrocatalysts for the reduction of dioxygen to water or hydrogen peroxide in air-saturated aqueous solutions containing 1 M HClO(4). The catalytic reduction of O(2) with the same dyads was also investigated in the homogeneous phase using 1,1'-dimethylferrocene as a reductant in PhCN containing HClO(4). The examined compounds are represented as (PMes(2)CY)Co(2), where P = a porph…
Electrochemically-driven conformational shift in mono- and di-copper constrained macrotricyclic cyclen receptors
2008
International audience; An electrochemical study of mono- and di-copper constrained cyclen macrotricycles is presented. Electrochemical data in DMF solution indicate that the reduction of dinuclear complexes occurs in two steps in the -0.4 to -0.8 V vs.AgCl/Ag potential range yielding CuII CuI and CuI CuI species further reduced to Cu metal at highly negative potentials. Mononuclear complexes are reduced in two steps to CuI and Cu metal. Electrochemical data suggest that reduction of both mononuclear and dinuclear complexes approach a square scheme involving electrochemically-driven conformational shifts for metal ions. The presence of endo- and exo-forms of the complexes are revealed by ch…