Functionalization of saturated hydrocarbons. 14. Further studies on the mechanism of Gif-type systems

Barton, Derek H. R.; Halley, Frank; Ozbalik, Nubar; Schmitt, Martine; Young, Esme; Balavoine, G.

doi:10.1021/ja00200a037

Cited by 125 publications

(29 citation statements)

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“…All the appropriate blank experiments were carried out to show that secondary radicals, had they been formed at the lower oxygen pressures, would have been captured by the solvent pyridine. [6] Subsequently, potassium superoxide was reacted with F d I under argon and shown to give an iron species that also gave an adamantane selectivity of about 1 .O.…”

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confidence: 99%

Models for non-heme oxidation enzymes

Barton¹,

Taylor²

1996

Pure and Applied Chemistry

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The Gif systems for the selective functionalization of saturated hydrocarbons based on the reactions of superoxide with Feu and of hydrogen peroxide with FelI1 are described. [l] Both systems are relatively efficient, but not nearly so efficient as the electrochemical system developed in collaboration with Prof. G.Balavoine and Dr. Aurore Gref (Universite de Paris-Sud-Orsay, France).[2] All systems afford main1 ketones. This is an unusual selectivity which implies a non-radical mechanism. It has been proven for the FeIIl H202 system that the activation of the Fe*II is independent of the formation of ketone which comes from oxygen. The intermediate for the ketone is a hydroperoxide (derived from oxygen). [3] Recent mechanistic studies are reported. INI1pODUClTONThere is universal acceptance that the selective functionalization of saturated hydrocarbons is a research challenge of major proportions. Although paraffins are, as their name implies, usually considered to be inert, Nature has solved the problem of their functionalization using complexes of iron and, to a lesser extent of copper. The iron complexes are either heme based, as in the ubiquitous P450 enzymes, or non-heme based, as in the vitally important roline-4-hydroxylase and in the fascinating enzyme, methane monooxygenase. These enzymes contain one FJ1, or two FelI1 atoms bridged by an 0x0 bridge, respectively. Although the protein in these enzymes is responsible for their chemo-and stereo-selectivity, the fundamental activation of the iron should be seen also in appropriate models. Models of P450 enzymes have been known for decades and the work of J.T.Groves is particularly noteworthy in this respect. Models of non-heme iron enzymes are much less familiar and, until our publications on Gif type Chemistry, not efficacious.[5] USE OF SUPEROXIDE AND OF HKDROGEN PEROXIDEOur work started with the assumption that when, 3 billion years ago, the blue-green algae started to make oxygen, a unicellular form of life started to concert the oxidation of iron with the oxidation of saturated hydrocarbons. It is agreed that after 1 billion years of life under reductive conditions, the world was full of saturated hydrocarbons, FeI1 compounds and metallic iron, as well as, an abundance of hydrogen sulfide, since life was using the reduction of sulfate to sulfide as an energy source.So our first experiment to test our hypothesis was the oxidation of adamantane in pyridine with some acetic acid in the presence of iron powder, hydrogen sulfide and oxygen. Surprisingly, a major amount of adamantanone was formed and there was only minor formation of the tertiary alcohol. Later, we obtained the same results when we replaced the iron powder with zinc powder and added a catalytic amount of an FdI salt. This showed the unusual power of the iron species formed to make ketones as principal products. During systematic studies on adamantane oxidation, we examined the effect of reducing oxygen pressure. We were surprised to find that lowering the oxy en pressure increased th...

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confidence: 99%

Models for non-heme oxidation enzymes

Barton¹,

Taylor²

1996

Pure and Applied Chemistry

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“…When the secondary coupled product is prepared by a rational synthesis, it is completely stable under the reaction conditions. Indeed, secondary radicals, when generated by photolysis of the acyl derivatives of N-hydroxy-2-thiopyridone, show competitive partitioning between oxygen and pyridine as would be expected (7).…”

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Mechanism of the selective functionalization of saturated hydrocarbons by Gif systems: relationship with methane monooxygenase.

Barton

Csuhai

Doller

et al. 1990

Proc. Natl. Acad. Sci. U.S.A.

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GifIII, GifIV, and Go. In GoAggI these two reagents are naturally present. In GoAggII and GoAggIII, Fei"' plus H202 gives the same iron species. This formalism (Scheme I) is the same as that used in arguments about the mechanism of P450 oxidation (2,8).There are two well-known mechanisms for the selective oxidation of saturated hydrocarbons. The first is the Fenton reaction of H202 with Fe"l, which leads to the production of hydroxyl radicals (1). The second mechanism is the ironbased porphyrin system of the P450 enzymes. In porphyrin models, based on this system, alkoxy radical-like chemistry is clearly seen (2). Thus, saturated hydrocarbons are attacked with a selectivity normal to radical reactions (tertiary> secondary>primary), sulfides are oxidized to sulfoxides, and olefins are epoxidized (3, 4).The family of Gif systems for the selective substitution of saturated hydrocarbons has very different reactivity from any prior process (5, 6). We first define (7) the systems: GifIII consists of iron powder suspended in pyridine-acetic acid with oxygen as oxidant. GiflV is similar but has an Fe"l catalyst with suspended zinc dust as a source ofelectrons and again oxygen is the oxidant. The Gif-Orsay (Go) electrochemical system replaces the zinc dust in GiflV by the cathode of an electrochemical cell. This system has a good coulombic yield (up to 50%). More recently, three new systems have been added: GoAggI, GoAggII, and GoAggIII. The GoAggI system consists of pyridine-acetic acid with stoichiometric Fell and K02 under argon. The GoAggII system is the same except that the oxidant is hydrogen peroxide and the catalyst is FeCl3 or other Fe"' salt.As will be described in more detail later, the addition of picolinic acid and its congeners has a major effect on the rate of oxidation of saturated hydrocarbons while preserving the characteristic Gif selectivity. The system using Fe"' plus H202 in the presence of picolinic acid or other special ligand is now referred to as GoAggIII. The names are geographical: G is for Gif-sur-Yvette, 0 is for Orsay, and Agg is for "Aggieland," where the last three systems were developed.Fe" +°j - In the Go, GoAggI, GoAggII, and GoAggIII systems it is clear that pyridine is not being reduced to dipyridyls or other pyridine-derived species. The role of the pyridine is to act as a ligand and to prevent hydroxyl radical-induced autooxidation chains.With certain hydrocarbons (adamantane, cis-and transdecalins, and the steroid side chain) radicals have been detected but only at tertiary positions, not at secondary positions. In adamantane, tertiary radicals can be detected by competitive attack on oxygen and on pyridine. The reduction of oxygen pressure increases the amount of attack of the tertiary radicals on the pyridine. However, the selectivity (C2/C3, where C2 = total of secondary oxidation products and C3 = total oxidation and pyridine-coupled products) is always constant. Coupling at the secondary position is not seen. When the secondary coupled product is prepared by a rational synt...

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“…Complex 1 absorbs one mole of O 2 per mole of the complex to form a mixed (III, V) valence oxygenated species 2, where oxygen coordinates more likely to one of the Ru III centers. A concerted cleavage of O-O bond and subsequent oxygen atom transfer to a possible Ru=C bond [15,16] gives ketone.…”

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confidence: 99%

Ruthenium complex catalyst system for selective oxidation of cyclohexane to cyclohexanone by molecular oxygen

Shukla

2005

React Kinet Catal Lett

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The ruthenium complex catalyst system RuCl 3 -pyridine-acetic acid-O 2 , was found to be efficient to activate C-H bond of cyclohexane and O 2 in the oxidation of cyclohexane. The oxidation of cyclohexane conducted at 30 0 C and 1 atm pressure of O 2 gave cyclohexanone with traces of cyclohexanol. Formation of µ-oxo binuclear Ru III complex was found to catalyze the oxidation of cyclohexane in which the rate of oxidation was found to increase on increasing the initial concentrations of catalyst and cyclohexane and partial pressure of O 2 .

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Functionalization of saturated hydrocarbons. 14. Further studies on the mechanism of Gif-type systems

Abstract: In the description of GoAgg1 and GoAgg11, we use the same geographical connotations as before. G stands for Gif, O is for Orsay, and Agg is for Texas A&M, College Station, where the work described in this paper was carried out. This kind of nomenclature saves space.

Cited by 125 publications

References 3 publications

Models for non-heme oxidation enzymes

Models for non-heme oxidation enzymes

Mechanism of the selective functionalization of saturated hydrocarbons by Gif systems: relationship with methane monooxygenase.

Ruthenium complex catalyst system for selective oxidation of cyclohexane to cyclohexanone by molecular oxygen

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