Phosphines oxygen atom transfer

Compounds of the composition [ReOCl3(N N)] have also been isolated with pyridine-2-aldi-mine and rr-acidic arylazopyridine and arylazoimidazole ligands." The products (101) are readily reduced by oxygen atom transfer reactions from Re to phosphorus atoms of phosphines which results in the formation of rhenium(III) complexes. Depending on the reaction condition and the phosphines used either mononuclear or binuclear compounds are formed." " Azo splitting reactions with arylazopyridines give access to arylimido and binuclear oxo/imido com-plexes. "" ... 

For practical reasons the two-electron oxidations of such prototypical substrates as alkenes, sulfides, amines and phosphines with peroxynitrous acid have been smdied since this type of oxygen atom transfer reaction is similar to the corresponding oxidations with peroxyformic acid, where both experimental and computational data are available The oxidative reactions (equations 3-6) of these key substrates can... 

Chromium(III) salen will form chromium(V) derivatives in much the same way as porphyrin complexes do. By reaction of iodosylbenzene with chromium(III)salen oxochromium(V) complexes are obtained (equation 74) which will effect oxygen atom transfer to phosphines and alkenes such as norbornene (equation 75) in stoichiometric and catalytic systems.1270 The... 

Read s group (86, 87) are studying some interesting co-oxidation reactions catalyzed particularly by RhCl(PPh3)3 in benzene at 20°C. Terminal olefins and triphenylphosphine are converted by 02 to the corresponding methyl ketones and the phosphine oxide. Radical chain processes were not detected, and such reactions normally do not yield methyl ketone products. Net oxygen-atom transfers were considered to result via the mechanism shown in Scheme 3. 

The Schiff bases (23), (43), and (44) formed Mo complexes of the type cw,wgr-[Mo02(ligand)] (which was associated in the solid state) and cw,mer-[Mo02(ligand)L] (L = neutral donor). The structures, electrochemical and chemical properties of these complexes, and their oxygen-atom transfer capabilities were extensive studies. These species were generally more active catalysts than their N-O-O-donor atom Schiff base counterparts, but oxygen-atom abstraction reactions with tertiary phosphines led to dinuclear Mo species rather than monomeric Mo complexes. 

The possible role of oxygen atom transfer in molybdenum enzyme catalysis was recognized in the early 1970s (190-194). In the ensuing years, a wealth of chemistry has established molybdenum as the premier exponent of such reactions (7, 195). Importantly, related dioxo-Mo(VI) and oxo-Mo(IV) complexes are interconverted by oxygen atom transfer reactions (Eq. (13)). These reactions are effected by reductants (X) such as tertiary alkyl and aryl compounds of the group 15 elements (especially phosphines) and oxidants (XO) such as S- and N-oxides. In many cases, however, the Mo(VI) and Mo(IV) compounds participate in a comproportionation reaction yielding dinuclear Mo(V) complexes (Eq. (15)). 

Oxygen atom transfer reactions from metal-oxo species to phosphines (forming phosphine oxides), alkylsulfides (forming sulfoxides), olefins (forming epoxides), and other substrates depend on the relative X=0 bond dissociation energies in the metal-oxo starting material and the oxidized product the reactivity scale based on bond dissociation energies was proposed.62... 

The porphyrin complex Mo02(tpp) also reacts with phosphines to form phosphine oxides or with secondary alcohols to produce ketones. The latter reaction appears to occur by one-electron (radical) steps showing the versatile reactivity of the Mo-oxo-porphyrin grouping. A one-electron oxidation of Mo02(tpp) forms the radical cation which readily undergoes oxygen atom transfer to yield the Mo complex MoO(tpp). The reaction has some features in common with those of cytochrome P450. ... 

The primary focus of research using transition metal phosphine complexes for oxidations is in the complexation and activation of molecular oxygen. These oxygen complexes have been variously regarded as complexes of coordinated peroxide, superoxide, or singlet oxygen, and their reactivity with reduced substrate has been interpreted on such a basis. In this chapter, we will focus on the chemical reactivity of these compounds for oxygen atom transfer oxidation reactions, with a particular emphasis on the mechanistic features of these processes. 

OXYGEN ATOM TRANSFER FROM METAL PHOSPHINE HYDROPEROXIDES AND SUPEROXIDES... 

Oxygen atom transfer to alkene [363] and phosphine [366] initiated by a light irradiation to Fe porphyrin m-oxo dimer was reported (Fig. 36). Epoxidation of alkene initiated by light irradiation to an oxygen conq>lex of Nb or Mo porphyrins was observed to be promoted by molecular oxygen [367-369] (Rg. 37). 

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