Coordinated molecular oxygen, reactions

The mechanism of this unusual process has been studied in some detail. Absolute rate constants for the spontaneous reaction of (TMSlgSiH with molecular oxygen (Reaction 33) has been determined to be at 70 °C and theoretical studies elucidate the reaction coordinates. ... 

Reactions of Coordinated Molecular Oxygen. Several complexes, notably tertiary phosphine complexes of Ru°, Rh1, Ir1 and Pt° react with oxygen to... 

It should be pointed out, however, that although many of the dioxygen complexes react readily with SO2 to give sulfato complexes, many of the analogous SO2 complexes react more slowly, or not at all with molecular oxygen. Reactions of coordinated CO also give rise to carbonate complexes except in the case of rhodium complexes which tend to form coordinated or free CO2, equations (47)-(50). 

The family of poly(pyrazol-l-yl)borates has been widely used as supporting ligands in nickel coordination chemistry.556,557 Complex (191) is an example, where unusual cysteine coordination is achieved at a tris(pyrazolylborate)nickel(II) template.601 (191) undergoes rapid reaction with molecular oxygen to presumably form a sulfinate. 

Oxidations dependent on molecular oxygen are of fundamental importance to many chemical and biochemical processes (1.-6). A large number of these processes require the presence of some transition metal ion to "activate" the oxygen. The initial step in many of these reactions is the coordination of O2, and the... 

Metal complexes catalyze oxidation of compounds having mobile hydrogens, such as ascorbic acid, hydroquinone, phenols, and amines, in the presence of molecular oxygen [Eq. (16)]. In this reaction, a substrate coordinates to the metal catalyst,... 

TiTany transition metal complexes react reversibly with molecular oxygen (1, 2) and with olefins (3, 4, 5). van Gaal et al. (6) recently prepared a group VIII metal complex which contains both oxygen and an olefin in the coordination sphere (Reaction 1). 

Popp B. V. Wendlandt J.E. Landis C. R. Stahl S. S. Reaction of molecular oxygen with an NHC-coordinated Pd° complex computational insights and experimental implications. Angew. Chem., Int. Ed. 2007, 46, 601-604. 

Under similar oxidative conditions, with activation of the aromatic C-H bond, some arenes could be used directly as aryl sources [41]. Unfortunately, by analogy with the Friedel-Crafts acylation, this reaction is regioselective for very few substrates only. High regioselectivity was, however, obtained if coordinating substituents on the arenes facilitate an orthopalladation reaction by a Pd(II) species [42]. After carbometallation and reductive elimination, Pd(0) is released, which has to be converted into the initial Pd(II) species in an extra oxidation step. Usually, quinines are used for this purpose, but in combination with certain heteropolyacids as cocatalysts even molecular oxygen can be employed as the oxidant. 

The most common pathway for catalysis of autoxidations by transition metal complexes involves the decomposition of alkyl hydroperoxides. Another route that may be possible for chain initiation involves direct oxygen activation, whereby the complexation of molecular oxygen by a transition metal would lower the energy of activation for direct reaction with the substrate [reaction (9)]. For example, oxygen coordinated to a metal might be expected to possess properties similar to alkylperoxy radicals and undergo hydrogen transfer with a hydrocarbon ... 

Direct reaction between oxygen and a substrate would be expected to be more favorable when both molecules are coordinated to a metal. Indeed, hydrogen abstraction from a coordinated olefin by coordinated dioxygen was observed in the reaction of a Rh(I)-cyclooctene complex with molecular oxygen.186a,b The following mechanism was proposed ... 

Superoxide ion ( 02 ) might be produced as the active oxygen from the Fe(II)-porphyrin and molecular oxygen system (binary system). However, superoxide (18-crown-6-complexed K02) in benzene does not react with skatole. If this reaction occurs to give FA, the reaction is stoichiometric and not catalytic. The substrate specificity mentioned above also excludes the possibility of oxygen activation via the 7r-coordinated skatole-Fe(II)-porphyrin-02 complex (I). So the oxygen activation in this reaction system seems to occur via a skatole-anion-coordinated-Fe(II)-porphyrin-02 complex (II). 

Immediately upon contact with air, the high-spin complex (g 6.1) attributable to Fe(III) TPP py (pentacoordinated complex) is observed together with the free radicals whose g values are 1.99-2.04 and the low-spin Fe(III) complex (see Figure 4). The formation of a pair of low-spin complexes attributable to the hexacoordinated Fe(III) TPP complexes (g = 2.66, 2.19, 1.80 and g = 2.31, 1.93) occurs with time. Of those, one should be the Fe(III) TPP py2 and another the product-coordinated Fe(III)-TPP complex. The appearance of ESR absorptions attributable to Fe(III) complexes (high-and low-spin) indicates that a part of the Fe(II)-TPP complex is converted to Fe(III) TPP by reaction with molecular oxygen. 

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