Mimoun complex

Djordjevic et al.464 have described the synthesis and characterization of amino acid complexes MoO(02)2Leq(OH2) (192) and the X-ray structures of the Gly, Ala, and Pro derivatives. Chiral ligands such as (R)/(S)-(194), (R)/(S)-(195), and (RR,S)/(R,SR)-(196) form Mimoun complexes, MoO(02)2L and MoO(02)2L(OH2). IR and 31P NMR data, as well as the X-ray structure of pentagonal bipyramidal MoO(02)2(R,R,.S -196)(OH2), indicate the presence of equatorial phos-phoryl donors.465,466 Enantioselectivity in the stoichiometric epoxidation of pro-chiral olefins was marginal (<10%) except in the case of the binaphthyl derivatives (L - 195) where e.e. s of up to 39% were recorded.4 Related structures are observed for phosphine oxide458,467 and chelate complexes such as MoO(02)2 OE(iPr)2CH2CH2OMe (197, E = P, As) 458 468 An efficient bipha-sic catalytic epoxidation system based on MoO(02)2(OPR3) (R = -dodecyl) has been developed and the activity of related complexes assessed.460 Earlier attempts to produce aqueous oxidants included the synthesis of water-soluble bpy derivatives.469,470... 

Key Words Ethylene oxide, Propylene oxide. Epoxybutene, Market, Isoamylene oxide. Cyclohexene oxide. Styrene oxide, Norbornene oxide. Epichlorohydrin, Epoxy resins, Carbamazepine, Terpenes, Limonene, a-Pinene, Fatty acid epoxides, Allyl epoxides, Sharpless epoxidation. Turnover frequency, Space time yield. Hydrogen peroxide, Polyoxometallates, Phase-transfer reagents, Methyltrioxorhenium (MTO), Fluorinated acetone, Alkylmetaborate esters. Alumina, Iminium salts, Porphyrins, Jacobsen-Katsuki oxidation, Salen, Peroxoacetic acid, P450 BM-3, Escherichia coli, lodosylbenzene, Oxometallacycle, DFT, Lewis acid mechanism, Metalladioxolane, Mimoun complex, Sheldon complex, Michaelis-Menten, Schiff bases. Redox mechanism. Oxygen-rebound mechanism, Spiro structure. 2008 Elsevier B.V. 

The reaction of Mo species with H2O2 forms peroxide complexes known as Mimoun complexes (Fig. 1.11a). These are not as active as organic hydroperoxides Mo-OOR in epoxidation. Peroxo complexes have been reviewed [464]. 

Gonzalez-Navarrete P, Sensato F, Andres J, Longo E (2014) Oxygen atom transfer reactions from mimoun complexes to sulfides and sulfoxides. A bonding evolution theory analysis. J Phys Chem A... 

Extended Hiickel theory (EHT) was applied to study the decomposition of the five-membered metallacycle intermediate proposed by Mimoun for the epoxidation by Mo bisperoxo complexes [44, 45]. Another EHT study [40] proposed the coordination of ethene to the metal center of an MoO(02)2 complex as the first step, followed by a slipping motion of ethene toward... 

In the earlier volume of this book, the chapter dedicated to transition metal peroxides, written by Mimoun , gave a detailed description of the features of the identified peroxo species and a survey of their reactivity toward hydrocarbons. Here we begin from the point where Mimoun ended, thus we shall analyze the achievements made in the field in the last 20 years. In the first part of our chapter we shall review the newest species identified and characterized as an example we shall discuss in detail an important breakthrough, made more than ten years ago by Herrmann and coworkers who identified mono- and di-peroxo derivatives of methyl-trioxorhenium. With this catalyst, as we shall see in detail later on in the chapter, several remarkable oxidative processes have been developed. Attention will be paid to peroxy and hydroperoxide derivatives, very nnconunon species in 1982. Interesting aspects of the speciation of peroxo and peroxy complexes in solntion, made with the aid of spectroscopic and spectrometric techniqnes, will be also considered. The mechanistic aspects of the metal catalyzed oxidations with peroxides will be only shortly reviewed, with particular attention to some achievements obtained mainly with theoretical calculations. Indeed, for quite a long time there was an active debate in the literature regarding the possible mechanisms operating in particular with nucleophilic substrates. This central theme has been already very well described and discussed, so interested readers are referred to published reviews and book chapters . 

Mimoun has already pointed out clearly that dioxygen carriers, even when reversibly formed, are not different from peroxo complexes prepared from hydrogen peroxide. As a... 

Synthesis of bimetallic /r-peroxo complexes has been described by Mimoun. In particular, for Co species reaction between a superoxo complex with a reduced metal is a feasible method, for Pt species acid catalyzed hydrolysis of peroxo complex may be used and for Rh or Pd the protocol implies reaction of potassium superoxide with appropriate precursors. 

The intermediate formation of alkyl peroxide complexes has been postulated, and in several cases observed with spectroscopic and spectrometric techniques in several selective procedures based on metal catalyzed oxidation with hydroperoxides, Ti and V ions being among the transition metals most widely used for this purpose. However, to date the few examples of alkyl peroxide complexes isolated and characterized in the solid state refer to (dipic)V0(00Bu-f)(H20) 8, synthesized by Mimoun and coworkers in 1983, and to a dimeric Ti complex [((/7 -OOBu-f)titanatrane)2(CH2Cl2)3] 9, synthesized by Boche and coworkers. ... 

At odds with other similar peroxo metal complexes, V0(02)pic(H20)2, 36, performs non-selective epoxidation reactions. On this occasion Mimoun proposed a mechanism where a homolytic rupture of one metal-peroxo oxygen bond produces the active oxidant (Scheme 14). When aromatic substrates are allowed to react with 36, hydroxylation reaction takes place by way of the same active species as indicated in Scheme 15. 

Mimoun and coworkersdescribed the first well-defined example of a d° metal aUtylperoxidic species 49 which epoxidized simple olefins with high selectivity. Several features of the epoxidation performed by 49 resemble those of the Halcon catalytic epoxidation process " . Novel tungsten complexes containing 2 -pyridyl alcoholate ligands like 50 have been synthesized and tested as catalysts in the epoxidation of cw-cyclooctene with TBHP in the absence of solvent . The system displayed modest catalytic activity (100% conversion in 60 h) but excellent product selectivity. 

One of the breakthroughs in the field was reported in 1983 by Mimoun and coworkers . On that occasion they reported the synthesis, characterization and radical reactivity of a class of vanadium peroxo complexes representative of which is the species V0(02)pic (HaOIa, 36. The oxidative ability of this complex has been tested with several aliphatic and aromatic hydrocarbons and the synthetic results obtained can be summarized as in Scheme 20. 

Co(ni) alkyl peroxides have been prepared and used by Mimoun and coworkers in the hydroxylation of hydrocarbons with this metal a Haber-Weiss type of reactivity is suggested. Square-planar Pt(II) complexes, of the type [(dppe)Pt(CF3)(solv)], used by Strukul in the epoxidation of alkenes and in Baeyer-Villiger oxidations of ketones (Schemes 8 and 9), are effective catalysts also in the direct hydroxylation of aromatics with hydrogen peroxide. The reactivity increases in the presence of electron releasing substituents in the aromatic ring. Ortho and para derivatives are practically the only products observed and interesting selectivity toward the ortho products has been detected (equation 85). 

Mimoun H (1987) Metal Complexes in Oxidation. In Wilkinson G, Gillard RD, McCleverty JA (eds) Comprehensive Coordination Chemistry, vol 6, chap 61.3. Pergamon Press, Oxford, p 317... 

Mimoun proposed a mechanism that is general for both stoichiometric epoxidations with peroxo complexes and for catalytic systems employing alkyl hydroperoxides.292-294 It involves an alkylperoxidic species with the alkene complexed through the metal ... 

The metallacycle mechanism can also be considered a concerted mechanism. It is analogous to the one proposed for metal peroxo complexes and is based on the assumed formation of a cyclic intermediate that includes the peroxo group, the reactant molecule, and the metal ion (Mimoun, 1982, 1987 Huybrechts et al., 1992). For alkene epoxidation, the sequence of events would be represented as follows [Eq. (31)] ... 

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