Search results for "PHOTOCHEMISTRY"
showing 10 items of 2034 documents
Alcohol oxidation by dioxygen and aldehydes catalysed by square-planar cobalt(III) complexes of disubstituted oxamides and related ligands
2001
The square-planar cobalt(III) complexes of o-phenylenebis(N′-methyloxamidate) (Me2opba) and related oxamate (Meopba) and bis(oxamate) (opba) ligands catalyse the selective oxidation, by dioxygen and pivalaldehyde, of a wide range of secondary alcohols to the corresponding ketones, in good yields and under mild conditions in acetonitrile at room temperature. Thus, the oxidation of the series of α-alkylbenzyl alcohols PhCH(OH)R (R = Me, Et, iPr, tBu) results in the exclusive formation of ketones as a product of C−H bond cleavage, and no C−C bond cleavage products are observed in any case. The modulation of catalytic activity by ligand substituents among this series of cobalt catalysts highlig…
The Kinetic Stability of Cationic Benzyl Titanium Complexes that Contain a Linked Amido-Cyclopentadienyl Ligand: The Influence of the Amido-Substitue…
2002
Cationic benzyl titanium complexes [Ti(η 5 : η 1 -C 5 Me 4 SiMe 2 NR')-(CH 2 Ph)] + were cleanly formed by the reaction of the dibenzyl titanium complexes [Ti(η 5 : η 1 -C 5 Me 4 SiMe 2 NR')(CH 2 Ph) 2 with B(C 6 F 5 ) 3 and [Ph 3 C][B(C 6 F 5 ) 4 ] in bromobenzene. NMR spectroscopic studies suggest that the benzyl titanium cations contain a fluxional η 2 -coordinated benzyl ligand. Kinetic analysis showed that the benzyl titanium cations decompose according to first-order kinetics and that the amido substituents R' (R' = Me, i Pr, t Bu) in the linked amido-cyclopentadienyl ligand influence the lability of these benzyl titanium cations. The order of the kinetic stability of the benzyl titan…
More electron rich than cyclopentadienyl: 1,2-diaza-3,5-diborolyl as a ligand in ferrocene and ruthenocene analogs
2011
Ruthenium and iron sandwich complexes incorporating cyclopentadienyl analogs with CB(2)N(2)(-) skeletons were characterized. Electrochemical measurements supported by computational studies revealed that in combination with larger metal ions such as Ru the CB(2)N(2)(-) ligand can be more electron-rich than its organic counterpart.
Equilibrium and kinetics studies on bibrachial lariat aza-crown/Cu(II) systems reveal different behavior associated with small changes in the structu…
2014
Abstract The high-yield synthesis of a new bibrachial lariat azacrown constituted by two tris(2-aminoethyl)amine (tren) units functionalized in one of its arms with a 4-methylquinoline group linked by dimethylene pyridine spacers (L2) is reported for the first time. The speciation studies show formation of mono- and binuclear Cu2+ complexes of similar stability. Comparisons are established with the complexes formed by the precursor tren-quinoline derivative (L4) and with the previously reported ligands containing naphthalene instead of quinoline as the fluorophore (L1, L3). The kinetics of formation and decomposition of Cu2+ complexes with L1 and L2 has been studied. For L1, the acid-promot…
Monitoring Thiol–Ligand Exchange on Au Nanoparticle Surfaces
2018
Surface functionalization of nanoparticles (NPs) plays a crucial role in particle solubility and reactivity. It is vital for particle nucleation and growth as well as for catalysis. This raises the quest for functionalization efficiency and new approaches to probe the degree of surface coverage. We present an (in situ) proton nuclear magnetic resonance (1H NMR) study on the ligand exchange of oleylamine by 1-octadecanethiol as a function of the particle size and repeated functionalization on Au NPs. Ligand exchange is an equilibrium reaction associated with Nernst distribution, which often leads to incomplete surface functionalization following “standard” literature protocols. Here, we show…
UV photostability of metal phthalocyanines in organic solvents
2003
Kinetic studies of photochemical reactions induced by UV radiation in solutions of metal phthalocyanines have been carried out to determine the factors which might have influenced the stability of photosensitized phthalocyanines. Complexes of the molecular type Mpc, M'(2)pc, and Lnpc(2) (where M = Li, Mg, Fe, Co, Zn, Pb; M'= Tl; Ln = rare earth; pc = phthalocyanine ligand, C(32)H(16)N(8)(2-)) were investigated in DMF, DMSO, and pyridine. Progressive decay of the phthalocyanine macrocycle due to absorption of UV light was observed. Phthalimide found in the final photolysis product may indicate some chemically bonded oxygen involved in the solid phthalocyanine material. Fluorescence lifetimes…
Spectroscopic, magnetic, and electrochemical studies of a dimeric N-substituted-sulfanilamide copper(II) complex. X-ray and molecular structure of th…
2010
Abstract A dinuclear copper(II) complex with a N-substituted sulfonamide as ligand has been investigated. The new N-(pyridin-2-yl)biphenyl-4-sulfonamide ligand has been prepared and structurally characterized. The copper(II) complex has been synthesized and its crystal structure, magnetic properties and EPR spectra were studied in detail. The metal centers are bridged by four nonlinear triatomic NCN groups. The coordination geometry of the copper(II) ions in the dinuclear entity is distorted square planar with two N-pyridyl and two N-sulfonamido atoms. Magnetic susceptibility data show a moderate antiferromagnetic coupling, with −2 J = 284 cm−1. The EPR spectrum of the polycrystalline sampl…
Resonance Raman Studies of Bis(terpyridine)ruthenium(II) Amino Acid Esters and Diesters
2009
Resonance Raman (rR) spectroscopy in combination with DFT calculations was used to elucidate the nature of the 1metal-to-ligand charge-transfer states (1MLCT) of ester derivatives of homo- and heteroleptic bis(terpyridine)ruthenium(II) complexes [RuII(tpy–COOC2H5)(tpy–R)](PF6)2 with R = NH2 (1a), R = COOC2H5 (1b) and R = NHCOCH3 (1c). The rR spectra provide evidence that the 1MLCT states of 1b and 1c are well described by the expected 1[(“t2g”)5{π*(tpy–COOC2H5)}1] electron configuration, while the 1MLCT state of the donor/acceptor-substituted complex 1a also involves the amine-substituted terpyridine ligand. The excited state of 1a can be described by a 1[{dyz/π(tpy–NH2)}1{π*(tpy–COOC2H5)}1…
Picosecond Time Resolved Analysis of the Fast and Slow Reversible Non-Photochemical Chlorophyll Fluorescence Quenching
1998
Photosystem II, which is a potential target of adverse effects of supersaturating light, is strongly dependent on a mechanism, which allows to switch over between efficient photochemical energy conversion at limiting light intensity and efficient photothermal energy conversion under strong light. The mechanisms for the thermal dissipation of light absorbed in excess are reflected by the socalled non-photochemical quenching of chlorophyll fluorescence (NPQ). Under excessive illumination two major components contribute to the overall NPQ which can be distinguished by their different kinetics of dark relaxation. The fast reversible component is supposed to be linked to the light-induced format…
Current Problems in the Modelling of Photochemical Reactors
1985
Photochemical reactors are examined from the point of view of the main problems connected to their modelling. By distinguishing the diverse meanings of kinetic models and the varied objectives in establishing models, a particular attention is devoted to the following aspects of homogeneous photoreactors: steady state condition, effect of stirring and mixing, effect of the shape of the reactor and of the position of the light source, light emission models, scale up. For the heterogeneous systems only general considerations on kinetic models in heterogeneous photocatalysis and on the problems related to the use of fluidized bed photoreactors are done.