One-electron oxidation of ferrocenes by short-lived N-oxyl radicals. The role of structural effects on the intrinsic electron transfer reactivities.

A kinetic study of the one electron oxidation of substituted ferrocenes (FcX: X = H, COPh, COMe, CO(2)Et, CONH(2), CH(2)OH, Et, and Me(2)) by a series of N-oxyl radicals (succinimide-N-oxyl radical (SINO), maleimide-N-oxyl radical (MINO), 3-quinazolin-4-one-N-oxyl radical (QONO) and 3-benzotriazin-4-one-N-oxyl radical (BONO)), has been carried out in CH(3)CN. N-oxyl radicals were produced by hydrogen abstraction from the corresponding N-hydroxy derivatives by the cumyloxyl radical. With all systems, the rate constants exhibited a satisfactory fit to the Marcus equation allowing us to determine self-exchange reorganization energy values (λ(NO˙/NO(-))) which have been compared with those previously determined for the PINO/PINO(-) and BTNO/BTNO(-) couples.

Structure and C-S bond cleavage in aryl 1-methyl-1-arylethyl sulfide radical cations.

Steady state and laser flash photolysis (LFP) of a series of p-X-cumyl phenyl sulfides (4-X-C(6)H(4)C(CH(3))(2)SC(6)H(5): 1, X = Br; 2, X = H; 3, X = CH(3); 4, X = OCH(3)) and p-X-cumyl p-methoxyphenyl sulfides (4-X-C(6)H(4)C(CH(3))(2)SC(6)H(4)OCH(3): 5, X = H; 6, X = CH(3); 7, X = OCH(3)) has been carried out in the presence of N-methoxy phenanthridinium hexafluorophosphate (MeOP(+)PF(6)(-)) under nitrogen in MeCN. Steady state photolysis showed the formation of products deriving from the C-S bond cleavage in the radical cations 1(+•)-7(+•) (2-aryl-2-propanols and diaryl disulfides). Formation of 1(+•)-7(+•) was also demonstrated by LFP experiments evidencing the absorption bands of the radical cations 1(+•)-3(+•) (λ(max) = 530 nm) and 5(+•)-7(+•) (λ(max) = 570 nm) mainly localized in the arylsulfenyl group and radical cation 4(+•) (λ(max) = 410, 700 nm) probably mainly localized in the cumyl ring.

Reaction of singlet oxygen with thioanisole in ionic liquid-acetonitrile binary mixtures.

A study of the reaction of thioanisole with singlet oxygen in different ionic liquid-acetonitrile binary mixtures has shown that ILs are able to accelerate the thioanisole sulfoxidation when used as additives. With imidazolium ILs, the maximum efficiency is reached at x(IL) ∼ 0.1-0.

N-demethylation of N,N-dimethylanilines by the benzotriazole N-oxyl radical: evidence for a two-step electron transfer-proton transfer mechanism.

The reaction of the benzotriazole N-oxyl radical (BTNO) with a series of 4-X-N,N-dimethylanilines (X = CN, CF(3), CO(2)CH(2)CH(3), CH(3), OC(6)H(5), OCH(3)) has been investigated in CH(3)CN. Product analysis shows that the radical, 4-X-C(6)H(4)N(CH(3))CH(2)(*), is first formed, which can lead to the N-demethylated product or the product of coupling with BTNO. Reaction rates were found to increase significantly by increasing the electron-donating power of the aryl substituents (rho(+) = -3.

Electron-transfer properties of short-lived N-oxyl radicals. Kinetic study of the reactions of benzotriazole-N-oxyl radicals with ferrocenes. Comparison with the phthalimide-N-oxyl radical.

A kinetic study of the one-electron oxidation of a series of substituted ferrocenes (FcX: X = H, COCH3, CO2Et, CH2OH, Et, and Me2) by the benzotriazole-N-oxyl radical (BTNO) and of ferrocene (FcH) by a series of ring-substituted benzotriazole-N-oxyl radicals (Z-BTNO: Z = H, 6-CF(3), 6-Cl, 6-Me, 6-MeO) has been carried out in CH3CN. N-Oxyl radicals were produced by hydrogen abstraction from 1-hydroxybenzotriazoles (Z-HBT) by the cumyloxyl radical produced after 355 nm laser flash photolysis of a solution of dicumyl peroxide in CH3CN. In both systems, the rate constants exhibited a satisfactory fit with the Marcus equation allowing us to determine self-exchange reorganization energy values for the BTNO/BTNO- couple, which resulted in good agreement: 34.

Reaction of singlet oxygen with thioanisole in ionic liquids: a solvent induced mechanistic dichotomy.

A study of the reaction of thioanisole with singlet oxygen in pyrrolidinium- and imidazolium-based ionic liquids has been carried out. In these solvents, thioanisole shows a strongly enhanced reactivity with respect to molecular aprotic solvents, probably due to a stabilization of the persulfoxide intermediate in the ionic medium. Product isotope effects suggest a mechanistic change ongoing from pyrrolidinium to imidazolium solvents.

Stereochemistry of the C-S bond cleavage in cis-2-methylcyclopentyl phenyl sulfoxide radical cation.

The TiO(2) photocatalyzed oxidation of cis-2-methylcyclopentyl phenyl sulfoxide in the presence of Ag(2)SO(4) in MeCN/H(2)O leads to the formation of 1-methylcyclopentanol, 1-methylcyclopentyl acetamide, and phenyl benzenethiosulfonate as the main reaction products. It is suggested that the C-S heterolysis in the radical cation is an unimolecular process leading to an ion radical pair. Fast 1,2-hydride shift in the secondary carbocation leads to 1-methylcyclopentyl carbocation that forms the observed products by reaction with H(2)O and MeCN.

Photosensitized oxidation of alkyl phenyl sulfoxides. C-S bond cleavage in alkyl phenyl sulfoxide radical cations.

The 3-cyano-N-methylquinolinium perchlorate (3-CN-NMQ(+)ClO4(-))-photosensitized oxidation of phenyl alkyl sulfoxides (PhSOCR1R2R3, 1, R1 = R2 = H, R3 = Ph; 2, R1 = H, R2 = Me, R3 = Ph; 3, R1 = R2 = Ph, R3 = H; 4, R1 = R2 = Me, R3 = Ph; 5, R1 = R2 = R3 = Me) has been investigated by steady-state irradiation and nanosecond laser flash photolysis (LFP) under nitrogen in MeCN. Steady-state photolysis showed the formation of products deriving from the heterolytic C-S bond cleavage in the sulfoxide radical cations (alcohols, R1R2R3COH, and acetamides, R1R2R3CNHCOCH3) accompanied by sulfur-containing products (phenyl benzenethiosulfinate, diphenyl disulfide, and phenyl benzenethiosulfonate). By laser irradiation, the formation of 3-CN-NMQ(*) (lambda(max) = 390 nm) and sulfoxide radical cations 1(*+) , 2(*+), and 5(*+) (lambda(max) = 550 nm) was observed within the laser pulse.

A kinetic study of the reaction of N,N-dimethylanilines with 2,2-diphenyl-1-picrylhydrazyl radical: a concerted proton-electron transfer?

The reactivity of the 2,2-diphenyl-1-picrylhydrazyl radical (dpph*) toward the N-methyl C-H bond of a number of 4-X-substituted- N, N-dimethylanilines (X = OMe, OPh, CH 3, H) has been investigated in MeCN, in the absence and in the presence of Mg(ClO 4) 2, by product, and kinetic analysis. The reaction was found to lead to the N-demethylation of the N, N-dimethylaniline with a rate quite sensitive to the electron donating power of the substituent (rho (+) = -2.03).

Singlet oxygen promoted carbon-heteroatom bond cleavage in dibenzyl sulfides and tertiary dibenzylamines. Structural effects and the role of exciplexes.

The C-heteroatom cleavage reactions of substituted dibenzyl sulfides and substituted dibenzylcyclohexylamines promoted by singlet oxygen in MeCN have been investigated. In both systems, the cleavage reactions (leading to benzaldehyde and substituted benzaldehyde) were slightly favored by electron-withdrawing substituents with rho values of +0.47 (sulfides) and +0.

A kinetic study of the electron-transfer reaction of the phthalimide-N-oxyl radical (PINO) with ferrocenes.

A kinetic study of the one-electron oxidation of a series of ferrocenes (FcX: X = H, CO2Et, CONH2, CH2CN, CH2OH, Et, and Me2) by PINO generated in CH3CN by reaction of N-hydroxyphthalimide (NHPI) with the cumyloxyl radical produced by 355 nm laser flash photolysis of dicumyl peroxide has been carried out. Ferrocenium cations were formed, and the reaction rate was determined by following the decay of PINO radical at 380 nm as a function of the FcX concentration. Rate constants were very sensitive to the oxidation potential of the substrates and exhibited a good fit with the Marcus equation, from which a lambda value of 38.

The singlet oxygen oxidation of chlorpromazine and some phenothiazine derivatives. Products and reaction mechanisms.

A kinetic and product study of the reactions of chlorpromazine 1, N-methylphenothiazine 2, and N-ethylphenothiazine 3 with singlet oxygen was carried out in MeOH and MeCN. 1 undergoes exclusive side-chain cleavage, whereas the reactions of 2 and 3, in MeOH, afforded only the corresponding sulfoxides. A mechanism for the reaction of 1 is proposed where the first step involves an interaction between singlet oxygen and the side-chain dimethylamino nitrogen.

Thermal and photochemical racemization of chiral aromatic sulfoxides via the intermediacy of sulfoxide radical cations.

Efficient racemization of enantiomerically pure methyl aryl sulfoxides was obtained by N-methylquinolinium tetrafluoborate (NMQ+) sensitized photolysis and by one-electron oxidation catalyzed by tris(2,2'-bipyridyl)ruthenium(III) hexafluorophosphate.

Aryl sulfoxide radical cations. Generation, spectral properties, and theoretical calculations.

Aromatic sulfoxide radical cations have been generated by pulse radiolysis and laser flash photolysis techniques. In water (pulse radiolysis) the radical cations showed an intense absorption band in the UV region (ca. 300 nm) and a broad less intense band in the visible region (from 500 to 1000 nm) whose position depends on the nature of the ring substituent.

Dual pathways for the desilylation of silylamines by singlet oxygen.

[reaction: see text] A kinetic and product study has been carried out for the reactions of silylamines 1a and 1b with (1)O(2) in MeCN and (80:20) MeCN-MeOH. Indications suggesting an electron-transfer step following exciplex (I) formation have been obtained. However, the fate of the radical cation is solvent dependent.

Rates of C-S bond cleavage in tert-alkyl phenyl sulfide radical cations.

[reaction: see text] Radical cations of tert-alkyl phenyl sulfides 1-4 have been generated photochemically in MeCN in the presence of the N-methoxyphenanthridinium cation (MeOP(+)), and the rates of C-S bond cleavage have been determined by laser flash photolysis.

Sulfur radical cations. kinetic and product study of the photoinduced fragmentation reactions of (phenylsulfanylalkyl)trimethylsilanes and phenylsulfanylacetic acid radical cations.

Laser and steady-state photolysis, sensitized by NMQ+, of PhSCH(R)X 1-4 (R = H, Ph; X =SiMe3, CO2H) was carried out in CH3CN. The formation of 1+*-4+* was clearly shown. All radical cations undergo a fast first-order fragmentation reaction involving C-Si bond cleavage with 1+* and 2+* and C-C bond cleavage with 3+* and 4+*.

Electron-transfer mechanism in the N-demethylation of N,N-dimethylanilines by the phthalimide-N-oxyl radical.

The reactivity of the phthalimide N-oxyl radical (PINO) toward the N-methyl C-H bond of a number of 4-X-substituted N,N-dimethylanilines (X = OMe, OPh, CF(3), CO(2)Et, CN) has been investigated by product and kinetic analysis. PINO was generated in CH(3)CN by reaction of N-hydroxyphthalimide (NHPI) with Pb(OAc)(4) or, for the kinetic study of the most reactive substrates (X = OMe, OPh), with tert-butoxyl radical produced by 266 nm laser flash photolysis of di-tert-butyl peroxide. The reaction was found to lead to the N-demethylation of the N,N-dimethylaniline with a rate very sensitive to the electron donating power of the substituent (rho(+) = -2.

Reactivity of phthalimide N-oxyl radical (PINO) toward the phenolic O-H bond. A kinetic study.

The reactivity of the phthalimide N-oxyl radical (PINO) toward the OH bond of a series of substituted phenols was kinetically investigated in CH(3)CN. The reaction selectivity and the deuterium kinetic isotope effect were determined. Information on the kinetic solvent effect was also obtained with phenol as the substrate.

Oxygenation of benzyldimethylamine by singlet oxygen. Products and mechanism.

[reaction: see text] A product study of the reaction of benzyldimethylamine (1) with thermally and photochemically generated 1O2 in MeCN was carried out. Benzaldehyde and N-benzyl-N-methylformamide are the reaction products, oxygenation representing ca. 9% of the overall quenching of 1O2 by 1.

Steady-state and laser flash photolysis study of the carbon-carbon bond fragmentation reactions of 2-arylsulfanyl alcohol radical cations.

The N-methylquinolinium tetrafluoroborate (NMQ(+))-sensitized photolysis of the erythro-1,2-diphenyl-2-arylsulfanylethanols 1-3 (1, aryl = phenyl; 2, aryl = 4-methylphenyl; 3, aryl = 3-chlorophenyl) has been investigated in MeCN, under laser flash and steady-state photolysis. Under laser irradiation, the formation of sulfide radical cations of 1-3, in the monomeric (lambda(max) = 520-540 nm) and dimeric form (lambda(max) = 720-->800 nm), was observed within the laser pulse. The radical cations decayed by first-order kinetics, and under nitrogen, the formation of ArSCH(*)Ph (lambda(max) = 350-360 nm) was clearly observed.

Synthesis of sulfoxides by the hydrogen peroxide induced oxidation of sulfides catalyzed by iron tetrakis(pentafluorophenyl)porphyrin: scope and chemoselectivity.

The oxidation of sulfides with H(2)O(2) catalyzed by iron tetrakis(pentafluorophenyl)porphyrin in EtOH is an efficient and chemoselective process. With a catalyst concentration 0.03-0.

Electron transfer and singlet oxygen mechanisms in the photooxygenation of dibutyl sulfide and thioanisole in MeCN sensitized by N-methylquinolinium tetrafluoborate and 9,10-dicyanoanthracene. The probable involvement of a thiadioxirane intermediate in electron transfer photooxygenations.

Photooxygenations of PhSMe and Bu2S sensitized by N-methylquinolinium (NMQ+) and 9,10-dicyanoanthracene (DCA) in O2-saturated MeCN have been investigated by laser and steady-state photolysis. Laser photolysis experiments showed that excited NMQ+ promotes the efficient formation of sulfide radical cations with both substrates either in the presence or in absence of a cosensitizer (toluene). In contrast, excited DCA promotes the formation of radical ions with PhSMe, but not with Bu2S.

Lignin peroxidase-catalyzed oxidation of nonphenolic trimeric lignin model compounds: fragmentation reactions in the intermediate radical cations.

The H(2)O(2)-promoted oxidations of the two nonphenolic beta-O-aryl lignin model trimers 1 and 2, catalyzed by lignin peroxidase (LiP) at pH = 3.5, have been studied. The results have been compared with those obtained in the oxidation of 1 and 2 with the genuine one-electron oxidant potassium 12-tungstocobalt(III)ate.

Mechanism of the oxidation of aromatic sulfides catalysed by a water soluble iron porphyrin.

The oxygen atom transfer-electron transfer (ET) mechanistic dichotomy has been investigated in the oxidation of a number of aryl sulfides by H2O2 in acidic (pH 3) aqueous medium catalysed by the water soluble iron(III) porphyrin 5,10,15,20-tetraphenyl-21H,23H-porphine-p,p',p",p"'-tetrasulfonic acid iron(III) chloride (FeTPPSCl). Under these reaction conditions, the iron-oxo complex porphyrin radical cation, P+. Fe(IV)=O, should be the active oxidant.