- Photocatalytic CO2 Reduction by Trigonal-Bipyramidal Cobalt(II) Polypyridyl Complexes: The Nature of Cobalt(I) and Cobalt(0) Complexes upon Their Reactions with CO2, CO, or Proton
-
The cobalt complexes CoIIL1(PF6)2 (1; L1 = 2,6-bis[2-(2,2′-bipyridin-6′-yl)ethyl]pyridine) and CoIIL2(PF6)2 (2; L2 = 2,6-bis[2-(4-methoxy-2,2′-bipyridin-6′-yl)ethyl]pyridine) were synthesized and used for photocatalytic CO2 reduction in acetonitrile. X-ray structures of complexes 1 and 2 reveal distorted trigonal-bipyramidal geometries with all nitrogen atoms of the ligand coordinated to the Co(II) center, in contrast to the common six-coordinate cobalt complexes with pentadentate polypyridine ligands, where a monodentate solvent completes the coordination sphere. Under electrochemical conditions, the catalytic current for CO2 reduction was observed near the Co(I/0) redox couple for both complexes 1 and 2 at E1/2 = -1.77 and -1.85 V versus Ag/AgNO3 (or -1.86 and -1.94 V vs Fc+/0), respectively. Under photochemical conditions with 2 as the catalyst, [Ru(bpy)3]2+ as a photosensitizer, tri-p-tolylamine (TTA) as a reversible quencher, and triethylamine (TEA) as a sacrificial electron donor, CO and H2 were produced under visible-light irradiation, despite the endergonic reduction of Co(I) to Co(0) by the photogenerated [Ru(bpy)3]+. However, bulk electrolysis in a wet CH3CN solution resulted in the generation of formate as the major product, indicating the facile production of Co(0) and [Co-H]n+ (n = 1 and 0) under electrochemical conditions. The one-electron-reduced complex 2 reacts with CO to produce [Co0L2(CO)] with νCO = 1894 cm-1 together with [CoIIL2]2+ through a disproportionation reaction in acetonitrile, based on the spectroscopic and electrochemical data. Electrochemistry and time-resolved UV-vis spectroscopy indicate a slow CO binding rate with the [CoIL2]+ species, consistent with density functional theory calculations with CoL1 complexes, which predict a large structural change from trigonal-bipyramidal to distorted tetragonal geometry. The reduction of CO2 is much slower than the photochemical formation of [Ru(bpy)3]+ because of the large structural changes, spin flipping in the cobalt catalytic intermediates, and an uphill reaction for the reduction to Co(0) by the photoproduced [Ru(bpy)3]+.
- Shimoda, Tomoe,Morishima, Takeshi,Kodama, Koichi,Hirose, Takuji,Polyansky, Dmitry E.,Manbeck, Gerald F.,Muckerman, James T.,Fujita, Etsuko
-
supporting information
p. 5486 - 5498
(2018/05/17)
-
- Synthesis of 2,4-dibromopyridine and 4,4'-dibromo-2,2'-bipyridine. Efficient usage in selective bromine-substitution under palladium-catalysis
-
We report an efficient method for preparing 2,4-dibromopyridine and 4,4'-dibromo-2,2'-bipyridine from the corresponding nitroazine N-oxide in one step via a tandem nucleophilic substitution-N-oxide reduction process. The one step preparation of 4,4'-dihalo-2,2'-bipyridines from dihalopyridines via a Stille reaction is also described. 4,4'-Dibromo-2,2'-bipyridine undergoes selective mono- or disubstitution processes under palladium catalysis. This short synthetic procedure is an efficient and reliable process for preparing conjugated pyridine and 2,2'-bipyridine building blocks for applications in coordination chemistry and materials science.
- Garcia-Lago, Ramon,Alonso-Gomez, Jose-Lorenzo,Sicre, Cristina,Cid, Maria-Magdalena
-
-
- PYRIDYL SUBSTITUTED HETEROCYCLES USEFUL FOR TREATING OR PREVENTING HCV INFECTION
-
The present invention relates to pyridyl substituted heterocycles and hydro isomers thereof and pharmaceutical compositions thereof that inhibit replication and/or proliferation of HCV virus. The present invention also relates to the use of the pyridyl he
- -
-
-
- POTASSIUM ION CHANNEL BLOCKERS
-
The invention provides novel sulphonylurea, sulphonylthiourea and sulphonylguanidine compounds which have the ability to block potassium ion channels regulated by intracellular concentrations of ATP. Methods of synthesis, pharmaceutical compositions and methods for the treatment of conditions such as type II diabetes, cardiac arrhythmias, ischaemic and hypoxic cardiovascular incidents, and cancers are also claimed.
- -
-
-
- On the Mechanism of the Carbodesilylation of 4- or 5-Substituted 2-(Trimethylsilyl)pyridines
-
An "ylide mechanism" is proposed for the carbodesilylation of 2-(trimethylsilyl)pyridines with benzaldehyde.In contrast, 3- and 4-(trimethylsilyl)pyridines, react only in the presence of a base catalyst via pyridyl anions with electrophiles.The rates of the uncatalyzed carbodesilylation reactions of 4-substituted 2-(trimethylsilyl)pyridines 2 with benzaldehyde correlate very well with the resonance parameters of the substituents ?0R, whereas the rates of 5-substituted 2-(trimethylsilyl)pyridines 7 correlate with the inductive substituent parameters ?1 in the Taft equation.This is to our knowledge the first direct determination of the resonance parameters ?0R.Key Words: Pyridines, substituted 2-(trimethylsilyl)-, synthesis of, carbodesilylation of / Carbodesilylation / Rate constants
- Effenberger, Franz,Krebs, Andreas,Willrett, Peter
-
p. 1131 - 1140
(2007/10/02)
-