Dioxygen solid-state oxidation

The stereochemistry of dioxygen oxidation has been studied for the di-f-butyldimesityldisilene (3).93 Oxidation of (E)-3 produced ( )-59a, ( > 60a, and ultimately ( )-61a exclusively, showing that all the steps in the sequence are stereospecific with retention of configuration. (Similar oxidation of a mixture of ( > and (Z)-3 gave isomeric mixtures of 59a, 60a, and 61a having the same proportions of stereoisomers as in the starting material.) Oxidation of 3 was found to be stereospecific both in solution and in the solid state. 

The proposed mechanism is given in Scheme 15. Initially the dissociation of water, maybe trapped by the molecular sieve, initiates the catalytic cycle. The substrate binds to the palladium followed by intramolecular deprotonation of the alcohol. The alkoxide then reacts by /i-hydride elimination and sets the carbonyl product free. Reductive elimination of HOAc from the hydride species followed by reoxidation of the intermediate with dioxygen reforms the catalytically active species. The structure of 13 could be confirmed by a solid-state structure [90]. A similar system was used in the cyclization reaction of suitable phenols to dihydrobenzofuranes [92]. The mechanism of the aerobic alcohol oxidation with palladium catalyst systems was also studied theoretically [93-96]. 

Of the reactions listed in Table II, the only process that leads to a decrease of the energy of molecular oxygen is the formation of the free superoxide ion, Oj ( — 10.15 kcal/mol). The superoxide ion would therefore be expected to be the dioxygen species most commonly formed on oxide surfaces and in fact it is the species most studied, both in the bulk of various matrices and on surfaces. The other species (Oj and Oj ) are not stable in the gas phase, although they can be stabilized in the solid state (Table I) due to the additional coulombic stabilization from the lattice. 

The general profile of the dioxygen oxidation of tetraaryldisilenes is shown in Eq. (63).7 Both in the solid state and in solution, the initial oxidation product of a tetraaryldisilene is the corresponding 1,2-disiladioxetane 145, whose intramolecular isomerization gives the thermodynamically more stable 1,3-disiladioxetane 146. All the steps of the oxidation occur intramolecularly and with the retention of stereochemistry around the Si-Si bond. While a small amount of disilaoxirane 147 is produced in the oxidation in low-temperature solution, 147 is converted to 146 smoothly in the presence of excess oxygen. 

Dioxygen Related Ligands Iron Transport Siderophores Macrocyclic Ligands Oxides Solid-state Chemistry Oxygen Inorganic Chemistry Polyoxometalates Sol Gel Synthesis of Solids. 

Catalytic systems based on various metal oxides under MW-assisted, solvent-free, aerobic conditions were compared for benzyl alcohol oxidation (Table 18.6) [23]. The manganese oxides were prepared by solution-based or solid-state reaction procedures [24], while V2O5, CuO, Fe Og, C02O3, and NiO were obtained via sol-gel or precipitation methods [25]. The benzyl alcohol oxidation was performed in a glass reactor where the slurry of catalyst with alcohol was stirred under dioxygen pressure and MW irradiation (Scheme 18.10, Table 18.6). 

The bis-salicylaldehyde-imine cobalt(II) derivatives form adducts with dioxygen, both in solution and in solid state, without the metal ion or the ligand being irreversibly oxidized. By heating at 80-100° the oxygen is evolved quantitatively, the parent chelate is regenerated and the process can be repeated many times. 

Thus their air-stability is not simply a result of the slower rate of solid-state reactions even when solutions of (5)-6 were enriched with dioxygen there was stiU no oxidation over 24 h. The solution behavior indicates a trend towards resistance to air-oxidation with increasing 7c-conjugation. In solution, the naphthylphosphines 12 and 13 show similar levels of oxidation, with notable quantities of both... 

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