Photochemical Exchange Research Articles

Photochemistry of cis,trans-[PtIV(en)(I)2(CH3COO)2] complex in aqueous solutions

The photochemistry of aqueous solutions of the cis,trans-[PtIV(en)(I)2(CH3COO)2] complex (1) was studied by stationary photolysis, nanosecond laser flash photolysis and ultrafast kinetic spectroscopy in the time interval from hundreds of femtoseconds to minutes. It is shown that the multistage photolysis, including photochemical reactions of ligand exchange and photoreduction, involves in the fi rst step the formation of the cis-[IV(en)(I)2(CH3COO)2] complex with a quantum yield of 0.3 (irradiation at 282 nm). The further ligand exchange and photoreduction reactions occur with much lower quantum yields. The photochemical exchange of the acetate ion occurs in a time interval of ~100 ps with the much slower final step, being probably the acidic dissociation of the product. The key intermediate of the first step of the process was detected in the picosecond time range. Depending on the interpretation of the key intermediate nature, two possible mechanisms of the primary photochemical process are proposed.

Photochemical synthesis and spectroscopic studies of 3, 5-alkyl/aryl substituted-tetrahydro-2H-1,3,5-thiadiazine-2-thione and their complexes with M(CO)4(2:2- NBD) [M = Cr, Mo and W] as M(CO)4 transfer reagent

Fifteen new complexes, [M(CO)4(L)2] [M=Cr; Mo; W]; [L= met-DTTT; et-DTTT; n-pr-DTTT; ph-DTTT and benz-DTTT] have been synthesized by the photochemical exchange reaction of [(η2:2- NBD)M(CO)4] (M= Cr, Mo and W) with 3,5-dimethyl-tetrahydro-2H-1,3,5-thiadiazine-2-thione (met-DTTT), 3,5-diethyl-tetrahydro-2H-1,3,5-thiadiazine-2-thione (eth-DTTT), 3,5-di-n-propyl-tetrahydro-2H-1,3,5-thiadiazine-2-thione (n-pr-DTTT), 3,5-diphenyl-tetrahydro-2H-1,3,5-thiadiazine-2-thione (ph-DTTT), and 3,5-dibenzyl-tetrahydro-2H-1,3,5-thiadiazine-2-thione (benz-DTTT). The new complexes have been characterized by elemental analysis, FTIR, 1H NMR spectroscopy. The spectroscopic studies show that DTTT behaves as a monodentate ligand coordinating via the sulfur (C=S) donor atom. Key words: Metal carbonyl, 3,5-dimethyl-tetrahydro-2H-1,3,5-thiadiazine-2-thione, exchange reactions.

Reactivity of the “yl”-Bond in Uranyl(VI) Complexes. 1. Rates and Mechanisms for the Exchange between thetrans-dioxo Oxygen Atoms in (UO2)2(OH)22+and Mononuclear UO2(OH)n2-nComplexes with Solvent Water

The stoichiometric mechanism, rate constant, and activation parameters for the exchange of the "yl"-oxygen atoms in the dioxo uranium(VI) ion with solvent water have been studied using 17O NMR spectroscopy. The experimental rate equation, (-->)v= k(2obs)[UO2(2+)]tot2/[H+]2, is consistent with a mechanism where the first step is a rapid equilibrium 2U(17)O2(2+) + 2H2O<==>(U(17)O2)2(OH)2(2+) + 2H+, followed by the rate-determining step (U(17)O2)2(OH)2(2+) + H2O<==>(UO2)2*(OH)2(2+) + H2(17)O, where the back reaction can be neglected because the (17)O enrichment in the water is much lower than in the uranyl ion. This mechanism results in the following rate equation (-->)v= d[(UO2)2(OH)2(2+)]/dt = k(2,2)[(UO2)2(OH)2(2+)] = k(2,2*)beta(2,2)[UO2(2+)]2/[H + ]2; with k(2,2) = (1.88 +/- 0.22) x 10(4) h(-1), corresponding to a half-life of 0.13 s, and the activation parameters DeltaH++ = 119 +/- 13 kJ mol-1 and DeltaS++ = 81 +/- 44 J mol(-1) K(-1). *Beta(2,)2 is the equilibrium constant for the reaction 2UO2(2+) + 2H2O<==>(UO2)2(OH)2(2+) + 2H+. The experimental data show that there is no measurable exchange of the "yl"-oxygen in UO2(2+), UO2(OH)+, and UO2(OH)4(2-)/ UO2(OH)5(3-), indicating that "yl"-exchange only takes place in polynuclear hydroxide complexes. There is no "yl"-exchange in the ternary complex (UO2)2(mu-OH)2(F)2(oxalate)2(4-), indicating that it is also necessary to have coordinated water in the first coordination sphere of the binuclear complex, for exchange to take place. The very large increase in lability of the "yl"-bonds in (UO2)2(OH)2(2+) as compared to those of the other species is presumably a result of proton transfer from coordinated water to the "yl"-oxygen, followed by a rapid exchange of the resulting OH group with the water solvent. "Yl"-exchange through photochemical mediation is well-known for the uranyl(VI) aquo ion. We noted that there was no photochemical exchange in UO2(CO3)3(4-), whereas there was a slow exchange or photo reduction in the UO2(OH)4(2-) / UO2(OH)5(3-) system that eventually led to the appearance of a black precipitate, presumably UO2.

Isolation, X-ray structure and properties of an unusual pentacarbonyl(2,2′-pyridyl-quinoxaline) tungsten complex

The first example of a monodentate complexation of 2-(2′-pyridyl)quinoxaline ( pq) to a metal centre through N 4 is reported. Photochemical exchange of the THF ligand in W(CO) 5THF by pq yields W(CO) 5(N 4-pq) ( 1), where the potentially bidentate pq ligand coordinates in an unusual monodentate fashion. Complex 1 is isolated as orange crystals and fully characterized on the basis of NMR, IR, UV–Vis and emission spectroscopy. The structure of 1 was determined by X-ray analysis. W(CO) 5(N 4-pq) ( 1) crystallizes in space group P2 1/ n , monoclinic crystal system with α = 7.0237(5) Å, b = 10.4618(8) Å, c = 23.7768(18) Å, Z = 4 and V = 1731.9(2) Å 3. Complex 1 exhibits intramolecular CH⋯N and intermolecular CH⋯O hydrogen bonds between the CH groups and nitrogen atoms of quinoxaline and CH groups and oxygen atoms of carbonyls, respectively, resulting in a supramolecular architecture in solid state. The preference to N 4 as coordination site is discussed in terms of electronic interactions. Solutions of 1 emits dually at 77 K while they are moderately instable at room temperature, as 1 undergoes chelation via a first-order kinetic process to form W(CO) 4pq ( 2). The determined reaction rate of 1 in toluene is 2.3 × 10 −5 s −1 (at 298 K) and is compared with literature values for other W(CO) 5L (L:diimine) complexes.

Photoinduced synthesis and electrochemical properties of new ruthenium(mono)bipyridine dialkylcyanamide and propiononitrile complexes

Photochemical exchange of carbonyls was used to produce new ruthenium dialkylcyanamide and nitrile compounds [RuCl 2(bpy)(CO)(NCNMe 2)] ( 2), [RuCl 2(bpy)(CO)(NCNEt 2)] ( 3), and [RuCl 2(bpy)(CO)(NCEt)] ( 4) from trans(Cl)-[RuCl 2(bpy)(CO) 2] ( 1). The reaction energetics, steric effects and electronic effects induced by the dialkylcyanamide and nitrile ligands were studied using computational DFT methods and cyclic voltammetry. In all cases the photochemical exchange reaction favors rearrangement of the ligands and formation of the trans(Cl,L)-[RuCl 2(bpy)(CO)L] (L = NCNMe 2, NCNEt 2 or NCEt) isomer as the main products. The oxidation potential of the complexes decreases with the increase of the HOMO energy and of net electron-donor character of the ligands, the dialkylcyanamides (whose electrochemical Lever E L ligand parameter has been estimated) behaving as stronger net electron donors than propiononitrile or CO. The electronic effect of the dialkylcyanamide and nitrile ligands is also reflected into the HOMO–LUMO energy difference, which is slightly reduced compared to the original dicarbonyl compound 1. The computational results show that the geometry of the isomer plays also an important role in the determination of orbital energies.

Alkyl exchange reactions of organocobalt porphyrins. A bimolecular homolytic substitution reaction.

Reaction of organocobalt(III) porphyrins with a cobalt(II) complex of a distinguishable porphyrin or tetrapyrrole resulted in the reversible exchange of the organic axial ligand. The exchange reaction was facile in such solvents as benzene, toluene, dichloromethane, chloroform, and pyridine; was unaffected by total exclusion of light; was faster than would be expected for a homolytic process given known Co-C bond dissociation energies; and was of broad scope with respect to the organic ligand. Methyl, benzyl, primary alkyl, secondary alkyl, and acyl groups exchanged, but phenyl groups did not. The position of the exchange equilibrium was independent of the direction of approach and was nonstatistical. The relaxation to equilibrium appeared to be consistent with that of a second-order process. The rate of the reaction varied with the identity of the R group in the order Bzl > or = Me > Et approximately n-Pr > i-Pr > i-Bu > acetyl approximately neopentyl approximately 2-adamantyl. However, the total variation in reaction rates was remarkably small. Attempts to find evidence of free-radical intermediates by trapping with TEMPO or CO or by alkyl group interchange with an excess of an alkyl halide of a distinct alkyl group were unsuccessful over a time scale comparable to multiple half-lives of the exchange reaction. In addition, no rearrangement products were detected in exchange reactions of the 5-hexenyl group. Use of cobalt porphyrin reactants that were sterically encumbered on both faces with groups large enough to prevent formation of a bridged, Co-C-Co structure resulted in a 5 or more order of magnitude decrease in the rate of methyl exchange, if not its outright cessation, when run with total exclusion of light. The decrease in the rate of the thermal exchange process revealed the existence a slow photochemical exchange process that was driven by room lights. All evidence was consistent with a bimolecular S(H)2 mechanism for the thermal exchange mechanism.

A Novel Method for the Demetalation of Tricarbonyliron–Diene Complexes by a Photolytically Induced Ligand Exchange Reaction with Acetonitrile

The photochemical exchange of all three carbonyl ligands with acetonitrile converts tricarbonyliron–diene complexes into the very labile triacetonitrile-iron–diene complexes. These easily demetalate in high yields to the corresponding free ligands on injection of air at −30°C [Eq. (1)]. The novel demetalation procedure is applied to the tricarbonyliron complexes of cyclopentadienones, cyclohexa-1,3-dienes, and buta-1,3-dienes.

A Novel Method for the Demetalation of Tricarbonyliron-Diene Complexes by a Photolytically Induced Ligand Exchange Reaction with Acetonitrile.

The photochemical exchange of all three carbonyl ligands with acetonitrile converts tricarbonyliron-diene complexes into the very labile triacetonitrile-iron-diene complexes. These easily demetalate in high yields to the corresponding free ligands on injection of air at -30°C [Eq. (1)]. The novel demetalation procedure is applied to the tricarbonyliron complexes of cyclopentadienones, cyclohexa-1,3-dienes, and buta-1,3-dienes.

Photochemical exchange reactions of thymine, uracil and their nucleosides with selected amino acids.

AbstractThe photoinduced exchange reactions of thymine with lysine at basic pH, using 254 nm light, have been studied. Three products have been isolated, namely, 6‐amino‐2‐(1‐thyminyl)hexanoic acid (Ia), 2‐amino‐6‐(1‐thyminyl)hexanoic acid (IIa) and 1‐amino‐5‐(1‐thyminyl)pentane (IIIa). Compound IIIa was shown to be a secondary product, produced by photochemical decarboxylation of Ia. Photochemical reaction of thymine with glycine and alanine at basic pH led, respectively, to formation of 2‐(1‐thyminyl)acetic acid (Ic) and 2‐(1‐thyminyl)propionic acid (Id). Compounds Ic and Id underwent photolysis to produce the decarboxylated secondary products 1‐methylthymine and 1‐ethylthymine, respectively. Thymidine reacts photochemically with glycine and alanine to produce the same products.Irradiation of DNA in the presence of lysine at basic pH led to the formation of the same products formed in the thymine‐lysine system, namely Ia, IIa and IIIa.Uracil was found to undergo analogous photochemical exchange reactions with lysine to form 6‐amino‐2‐(1‐uracilyl) hexanoic acid (Ib), and 2‐amino‐6‐(1‐uracilyl)hexanoic acid (IIb). Compound Ib was found to undergo photodecarboxylation to form 1‐amino‐5‐(1‐uracilyl)pentane (IIIb), analogous to the secondary photoreaction of Ia. Photoreaction of uracil with 1,5‐diaminopentane (cadaverine) likewise led to formation of IIIb.

ETC: A Mechanistic Concept for Inorganic and Organic Chemistry

AbstractThe concept of electron transfer catalysis (ETC), or more specifically “Double Activation Induced by Single Electron Transfer” (DAISET) gives an opportunity to connect experimental facts never previously correlated. The first activation results from the transfer of an electron to (or from) a molecular species; the second activation results from the build‐up of a reaction chain able to reproduce the species formed in the first step. The starting point of this review is the SRN1 mechanism where principle and experimental diagnostic criteria are critically discussed. The thermal and photochemical exchange and substitution reactions of PtIV complexes are then reviewed together with the exchange reaction [AuCl4]−/Cl−, reactions with Grignard reagents and other organometallic reagents, as well as the redox behavior of electronically excited organic compounds. Photochemical applications, including solar energy conversion are discussed. New aspects are also presented for the mechanistic problem “SN2 reaction or SET process?” Moreover, the concept has significance for SH2 reactions at metal centers, molecule‐induced homolyses, reactions of complexes, as well as electrochemical processes.–Unless otherwise specified, only double activation (DAISET) processes will be discussed in this article.

A photochemical exchange reaction of Michler's ketone

A photochemical exchange reaction of Michler's ketone

Photochemical exchange of borazine with deuterium

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTPhotochemical exchange of borazine with deuteriumMelvin P. Nadler and Richard F. PorterCite this: Inorg. Chem. 1969, 8, 3, 599–604Publication Date (Print):March 1, 1969Publication History Published online1 May 2002Published inissue 1 March 1969https://doi.org/10.1021/ic50073a039RIGHTS & PERMISSIONSArticle Views26Altmetric-Citations9LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (591 KB) Get e-Alerts Get e-Alerts

Arylation of sodium salts of cyclopentadienylirondicarbonyl hydride by onium compounds

1. A new method to synthesize π-C 5H 5Fe(CO) 2C 6H 2 by the interaction of π-C 5H 5Fe(CO) 2Na and onium salts has been developed. 2. It has been shown that the formation of π-C 5H 5Fe(CO) 2C 6H 5 is accompanied by a competing redox reaction leading to [π-C 5H 5Fe(CO)2 2] 2. With phenyldiazoniumboron fluoride, the latter process is almost entirely predominant. 3. The photochemical exchange of a carbonyl ligand for a triphenylphosphine molecule is investigated in the case of π-C 5H 5Fe(CO) 2P(C 6H 5) 3C 6H 5. At 70° the reaction proceeds, together with formation of the iron-6-benzoyl complex. 4. It is found that [π-C 5H 5Fe(CO) 2] 2 undergoes a photochemical reaction with a mixture fo P(C 6H 5) 3 and C 6H 5I (no reaction is observed with either of the components taken individually) to give π-C 5H 5Fe(CO)[P(C 6H 5) 3] I. The reaction is assumed to proceed via the formation of an active complex resulting from the interaction of P(C 6H 5) 3 with C 6H 5I. 5. π-C 5H 5Fe(CO) 2I is found to exchange its CO-group for P(C 6H 5) 3 when UV-irradiated in the presence of the latter.

Thermal and photochemical exchange of iodine with trifluoro-methyl iodide

The thermal and photochemical exchange reactions between I2 and CF3I were investigated in the gas phase between 100 and 180°C. The homogeneous thermal and photochemical reactions are initiated by I atoms and the exchange proceeds by abstraction I+CF3I→CF3+I2(1) followed by CF3+I2→CF3I+I. The rate constant k1 is given by 109.6 exp(– 16000/RT) l. mole–1 sec–1. From the activation energy for (1), D(CF3–I) is 51.5 ± 0.5 kcal mole–1. Rotating sector measurements lead to a value for the apparent second-order rate constant of the I atom recombination, I+I+M →I2+M in the presence of CF3I of 5.1 ± 2.0 × 107 l. mole–1 sec–1 at 100°C.

Photochemical Exchange of Water between Cr(H2O)6+3 and Solvent1

Photochemical Exchange of Water between Cr(H₂O)₆⁺³ and Solvent¹

Kinetics of the Thermal and Photochemical Exchange between Benzyl Iodide and Iodine

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTKinetics of the Thermal and Photochemical Exchange between Benzyl Iodide and IodineMoshe Gazith and Richard M. NoyesCite this: J. Am. Chem. Soc. 1955, 77, 23, 6091–6098Publication Date (Print):December 1, 1955Publication History Published online1 May 2002Published inissue 1 December 1955https://doi.org/10.1021/ja01628a001RIGHTS & PERMISSIONSArticle Views114Altmetric-Citations19LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (852 KB) Get e-Alerts Get e-Alerts

Kinetics of the Photochemical Exchange between Iodine and Allyl Iodide

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTKinetics of the Photochemical Exchange between Iodine and Allyl IodideDonald J. Sibbett and Richard M. NoyesCite this: J. Am. Chem. Soc. 1953, 75, 4, 763–767Publication Date (Print):February 1, 1953Publication History Published online1 May 2002Published inissue 1 February 1953https://doi.org/10.1021/ja01100a002RIGHTS & PERMISSIONSArticle Views35Altmetric-Citations4LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (593 KB) Get e-Alerts Get e-Alerts

The Photochemical Exchange Reaction between Tin(II) and Tin(IV) in Hydrochloric Acid Solution1

The Photochemical Exchange Reaction between Tin(II) and Tin(IV) in Hydrochloric Acid Solution¹

The Primary Quantum Yield of Dissociation of Iodine in Hexane Solution

The primary quantum yield for the photo-dissociation of iodine in degassed hexane at 25° has been calculated from measurements of the mean lifetime of the chains involved in the exchange of iodine atoms with trans-diiodoethylene. The primary quantum yield to an accuracy of ±15 percent is 0.59 at 436 mμ and 0.37 at 578 mμ. The deviation of this quantity from unity is affected both by the ``primary recombination'' of atoms which fail to escape from the original ``cage'' of solvent molecules, and by the ``secondary recombination'' of the original atoms by diffusion during a time which is very short compared to that in which either is apt to encounter an atom from another molecule. The specific rate constant for the recombination of iodine atoms in hexane solutions has been determined and has been shown to be about one fifth of the rate constant for collision in the gas phase. The presence of air decreases the rate constant for the photochemical exchange of iodine with diodoethylene by a factor of four and increases the apparent mean lifetime of iodine atoms by a factor of one hundred.

Thermal and Photochemical Exchange Reactions of Bromine

Thermal and Photochemical Exchange Reactions of Bromine