Metal-oxygen bond acid cleavage

The acid cleavage of a metal oxygen bond in metal carboxylates and formates is a commonly used method for the preparation of formic and carboxylic acids. The facility of this reaction depends on the strength of the metal oxygen bond. Since it is desirable that this bond be cleaved rapidly in a catalytic cycle, our attention was restricted to metal complexes of the Fe,... 

Dioxygenases form the second class of biochemical oxidation systems. They often oxidize hydrocarbons selectively to carboxylic acids. These catalysts proceed through low valence states of the catalytic metal center and through radical-type elementary steps. The metal centers donate electrons to the oxygen molecule, so as to assist oxygen bond cleavage. 

The first step of the coordination-insertion mechanism (I) consists of the coordination of the monomer to the Lewis-acidic metal center (Fig. 3.7). The monomer subsequently inserts into one of the aluminum-alkoxide bonds via nucleophilic addition of the alkoxy group on the carbonyl carbon (11) followed by ring opening via acyl-oxygen cleavage (1) hydrolysis of the active metal-alkoxide bond leads to the formation of a hydroxyl end group, while the second chain end is capped with an isopropyl ester, as indicated by NMR characterization of the resulting polymers [48]. 

In work reported elsewhere (31) we have shown that the oxidation of styrene under mild conditions is promoted by many group VIII metal complexes. The product profile depends on the nature of the metal center and often differs from that observed when radical initiators are used (Table IX). Substantial quantities of styrene oxide are found in some cases but not in others (31). The epoxide which is formed, however, seems to arise via the co-oxidation of styrene and formaldehyde which is formed by oxidative cleavage of the double bond. Formaldehyde may be oxidized to performic acid or formylperoxy radicals which are efficient epoxidizing agents. Reactions of styrene with oxygen in the presence of group VIII complexes exhibit induction periods and are severely retarded by radical inhibitors (31). Thus, the initial step in the oxidation of styrene in the presence of the Ir(I),Rh(I), Ru(II), and Os(II) com-... 

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