Metal-catalyzed oxygen transfer

Figure 6B.5. Active species for metal-catalyzed oxygen-transfer reactions.

These metal porphyrin-catalyzed oxygen transfer reactions are con-... 

Imidoiodanes and especially A-tosyliminoiodanes, ArINTs (Section 2.1.12.4), have found broad synthetic application as useful nitrene precursors in transition metal catalyzed aziridination of aUcenes and amidation of various organic substrates [584, 761]. Mansuy and coworkers in 1984 first reported the aziridination of alkenes with tosyliminoiodane PhINTs in the presence of iron- or manganese-porphyrins [762]. This reaction has a mechanism similar to the metal-catalyzed oxygen atom transfer reactions of iodosylbenzene (Section 3.1.20) and involves a metal-nitrene complex as the intermediate. 

The initial observation, discussed above, that transition metal-substituted polyoxometalates could be used to catalyze oxygen transfer from iodosobenzene to organic... 

The reactions of aldehydes at 313 K [69] or 323 K [70] in CoAlPO-5 in the presence of oxygen results in formation of an oxidant capable of converting olefins to epoxides and ketones to lactones (Fig. 23). This reaction is a zeolite-catalyzed variant of metal [71-73] and non-metal-catalyzed oxidations [73,74], which utilize a sacrificial aldehyde. Jarboe and Beak [75] have suggested that these reactions proceed via the intermediacy of an acyl radical that is converted either to an acyl peroxy radical or peroxy acid which acts as the oxygen-transfer agent. Although the detailed intrazeolite mechanism has not been elucidated a similar type IIaRH reaction is likely to be operative in the interior of the redox catalysts. The catalytically active sites have been demonstrated to be framework-substituted Co° or Mn ions [70]. In addition, a sufficient pore size to allow access to these centers by the aldehyde is required for oxidation [70]. 

Hi. Cr, Mo, W. In contrast to group IV and V transition metals, the catalytic active oxidant is of another type for group VI transition metal-catalyzed epoxidations The transition-metal-oxo complexes, in which the oxygen that is transferred is bonded to the metal via a double bond, are the active oxidizing species. 

Berkessel and Sklorz screened a variety of potential co-ligands for the Mn-tmtacn/H202 catalyzed epoxidation reaction and found that ascorbic acid was the most efficient one. With this activator the authors could oxidize the terminal olefins 1-octene and methyl acrylate with full conversion and yields of 83% and 97%, respectively, employing less than 0.1% of the metal complex (Scheme 86). Furthermore, with E- and Z-l-deuterio-1-octene as substrates, it was shown that the oxygen transfer proceeded stereoselectively with almost complete retention of configuration (94 2%). Besides the epoxidation, also the oxidation of alcohols to carbonyl compounds could be catalyzed by this catalytic system (see also Section in.C). 

Several different organonitrogen compounds readily undergo metal-catalyzed oxidation using alkyl hydroperoxide or hydrogen peroxide as oxygen transfer agents. In 1961,... 

A major subset of equation 1, and the focus of much recent research for intellectual and practical reasons, is transition metal-catalyzed transfer of oxygen from oxygen donors (Table I) to organic substrates, equation 2, commonly referred to as 0X0 transfer oxidation or "oxygenation" in much of the recent literature. Equation 2 can proceed by one or more of several possible mechanisms. Two types of mechanism for equation 2 are predominant in the absence of autoxidation, however. The first type involves heterolytic (nonradical) activation and transfer of activated oxygen, usually from an alkylhydioperoxide, to a substrate by a metal center. The... 

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