Oxygen Atom Transfer Process Research Articles

Molybdenum-Oxo and Peroxo Complexes in Oxygen Atom Transfer Processes with O2 as the Primary Oxidant

Molybdenum-Oxo and Peroxo Complexes in Oxygen Atom Transfer Processes with O2 as the Primary Oxidant

Oxygen Atom Transfer Reactions from Isolated (Oxo)manganese(V) Corroles to Sulfides

A series of five free-base corroles were metalated and brominated to form 10 manganese(III) corroles. Two of the free-base corroles and six manganese(III) corroles were analyzed by X-ray crystallography, including one complex that may be considered a transition-state analogue of oxygen atom transfer (OAT) from (oxo)manganese(V) to thioansisole. Oxidation by ozone allowed for isolation of the 10 corresponding (oxo)manganese(V) corroles, whose characterization by (1)H and (19)F NMR spectroscopy and electrochemistry revealed a low-spin and triply bound manganese-oxygen moiety. Mechanistic insight was obtained by investigating their reactivity regarding stoichiometric OAT to a series of p-thioanisoles, revealing a magnitude difference on the order of 5 between the β-pyrrole brominated (oxo)manganese(V) corroles relative to the nonbrominated analogues. The main conclusion is that the (oxo)manganese(V) corroles are legitimate OAT agents under conditions where proposed oxidant-coordinated reaction intermediates are irrelevant. Large negative Hammett ρ constants are obtained for the more reactive (oxo)manganese(V) corroles, consistent with expectation for such electrophilic species. The least reactive complexes display very little selectivity to the electron-richness of the sulfides, as well as a non-first-order dependence on the concentration of (oxo)manganese(V) corrole. This suggests that disproportionation of the original (oxo)manganese(V) corrole to (oxo)manganese(IV) and (oxo)manganese(VI) corroles, followed by substrate oxidation by the latter complex, gains importance when the direct OAT process becomes progressively less favorable.

Lead corrole complexes in solution: Powerful multielectron transfer reagents for redox catalysis

Abstract The first observation of Pb(II)-complexes of corroles and their photoinduced oxidation to the corresponding Pb(IV)-derivatives is reported. These compounds display metal-centered redox chemistry in solution. Their potential for catalytic oxygen atom transfer processes is explored.

O19. Reactivity and mechanisms of heme coordinated NOx. Reductive nitrosylation and oxygen atom transfer processes

O19. Reactivity and mechanisms of heme coordinated NOx. Reductive nitrosylation and oxygen atom transfer processes

Characterization of a reduced molybdenum-oxo compound derived from an oxo-transfer process under stoichiometric conditions

The stoichiometric oxidation of phosphanes or alcohols by a Mo(VI)-dioxo complex ( 1) followed both by UV spectroscopy results in the formation of a Mo(V) dimer with two μ-oxo bridges and two terminal oxo functions ( 3). Its structure is determined by an X-ray analysis depicting a Mo–Mo bond well in accord with the diamagnetic character of the complex. The spectroscopic follow up of the oxygen atom transfer process shows clearly that complex 3 is the end product of a series of intermediates among which one ( 2) is postulated as being a geometrical isomer of 3.

Variable‐Valent Rhenium Chemistry of Conjugated Nitrogenous Ligands: Structure and Reactivity

AbstractThe valence states of particular concern in this review are VI–I and the ligand types are diimine, azoimine, imineamide and azooximeall bidentate and N,N‐coordinating. Metal reduction potentials and stability of oxidation states are subject to control via variation of the nature and extent of N,N‐chelation and coligation. Back‐bonding plays a major role in determining stability and isomer specificity, particularly in the valence domain III–I. Three types of mediated oxygen atom transfer processes have been scrutinized and modeled: from ReVO to tertiary phosphanes and variable‐spacer diphosphanes, from water to diimine and from oxime to metal/coligand. Other reactivity topics include isomerizations associated with ligand substitution, stable azo anion radical generation and azo cleavage. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

Functional model of oxomolybdoenzymes: Synthesis and characterization of a molybdenum complex with sulphur and pterin ligands exhibiting saturation kinetics with pyridine N-oxide

Redox reaction between 6-acetonylisoxanthopterin (H2pte) and [MoVIO2 (ssp)] [ssp = anion of 2-(salicylideneamino) benzenethiol] in CH3OH-C2H5OH medium produces a new mixed ligand compound [MoIV (ssp) (Hpte) (OCH3)] (1). It has been characterized by elemental analysis, ESMS data, UV-Vis, IR,1HNMR (1D and 2D) spectroscopy and cyclic voltammetry. Kinetics of formation of this compound as well as that of its reaction with pyridine N-oxide have been followed spectrophotometrically. Both the reactions follow substrate saturation kinetics and involve metal-centred oxygen atom transfer process. Large negative values of entropy of activation indicate the operation of associative mechanism.

A study on the transition state in the photooxygenations by aromatic amine N-oxides

Oxygen—atom transfer process in the photolysis of aromatic amine N-oxides was suggested to involve the primary oxygen—atom elimination from N-oxides to give “oxene” follwed by its reactions with the oxygen-acceptors.

Oxidation of organic sulphides - II. Interaction ofcyclohexyl methyl sulphide with hydroperoxides in hydrocarbons

Oxidations ofcyclohexyl methyl sulphide bycyclohexenyl andt-butyl hydroperoxides in hydrocarbon solvents simulate those in alcohols (part I) in that the sulphoxide yield is quantitative under all the conditions studied. They differ, however, in their kinetic characteristics, and the complexities of the hydrocarbon systems are found to vary remarkably with the hydroperoxide and with the solvent. The reaction withcyclohexenyl hydroperoxide in benzene orcyclohexane is insensitive to the presence of oxygen, evidences no free radical character, and has orders of one with respect to sulphide and two with respect to hydroperoxide. Acetic acid catalyzes the reaction and changes the hydroperoxide order from 2 to 1. Essentially the same oxygen atom transfer process as postulated in alcohols is believed to occur: in the absence of acid, the oxidant is a bimolecular hydroperoxide complex; in the presence of acid, the component molecule effecting the associated hydrogen transfer is displaced by an acid molecule which can per­form this function more efficiently. The reaction witht-butyl hydroperoxide in benzene proceeds faster in air than in a vacuum; the oxygen catalysis is less incyclohexane and absent incyclohexene. The reaction stoicheiometry remains the same in all cases. The addition of acetic acid, which catalyzes the reaction as indicated forcyclohexenyl hydroperoxide, completely eliminates the sensitivity to oxygen. Considering oxygen-free systems, the reaction orders with respect to the sulphide are 0∙7 in benzene, 0∙4 incyclohexane, and 0∙45 incyclohexene; the order with respect to hydroper­oxide is 2 throughout. The reactions are insensitive to free radical inhibitors. It is suggested that oxidation occurs by two concurrent mechanisms; one is the oxygen-atom transfer process referred to above; the other is formulated as a two-stage process involving a hydroperoxide-solvent complex as oxidant, the rate of complex formation being rate-determining. In benzene in the presence of oxygen, the sulphide order is higher (0∙9) and the hydro­peroxide order lower (1∙4); free radical inhibitors effectively repress oxygen catalysis. A free radical chain mechanism therefore appears to come into play in the presence of oxygen, and the postulated requirements of this to account for the unaltered stoicheiometry and the solvent effects are discussed.