Metals, activated acyl radicals

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]. 

Reaction of Ruthenium Carbonyls with Alkyl Radicals Boese and Goldman reported that in the presence of aryl ketones, d8 metal carbonyls such as Ru(CO)3(dmpe) mediate photocatalytic carbonylation of alkanes via a free radical mechanism.161 The activity was proposed to be initiated by the addition of an alkyl radical to the metal carbonyl and the formation of a metal-acyl radical intermediate. The transition states and the products of the reaction between alkyl radicals and ruthenium carbonyls were studied utilizing the B3LYP level of theory.162 The methyl addition to a carbonyl of Ru(CO)5 or Ru(CO)3(dmpe) was computed to be about 6 kcal/mol more exothermic than addition to free CO. 

Metalaracficafs A very recent approach to CO activation by Wayland" is the use of odd-electron metal complexes, such as the 17e species [Rh(TMP)j (where TMP = tetramesitylporphyrin). This reacts with CO to give [(TMP)Rh(n.-CO)Rh(TMP)] and [(TMP)Rh(M,-CO-CO)Rh(TMP)], presumably via an intermediate [(TMP)Rh(CO)] that behaves like an acyl radical (R—C O) and either dimerizes or combines with the starting metalaradical [Rh(TMP)J. 

The radical C-H transformation of ethers is generally initiated by a-hydrogen abstraction with highly reactive radicals generated from such initiators as peroxides [3a, g], photo-activated carbonyl compounds [3b—d], metallic reagents [3i, j], and redox systems [3f, h[. Various combinations of ethers, radical initiators, and radical acceptors (e.g. carbon-carbon multiple bonds) may be used as the reaction components [6], Several notable means of direct C-C bond formation via the radical a-C-H transformation of ethers involve the use of triflon derivatives [7], the phthalimide-N-oxyl (PINO) radical [8], 2-chloroethylsulfonyl oxime ethers [9], and N-acyl aldohydrazones [10],... 

Pericyclic electrochemical reactions are increasingly developed. They involve chain reactions with a radical cation as chain transferring step or the generation of reactive dienophiles (see Chapter 22, Sec. V). Transition metal complexes are increasingly applied in electrochemistry as electrocatalysts for reductive carboxylation [47], acylation or alkylation [41], or activation [51]. 

Recently, Grubbs and coworkers [272] have synthesized an active alkoxyamine by reaction of 2-methyl-2-nitrosopropane with 1-bromoethylbenzene, catalyzed by ligated CuBr in the presence of metallic copper. A purified alkoxyamine was used to initiate the radical polymerization of styrene and isoprene. Well-defined low polydispersity polymers formed with M /M =1.14 for polystyrene and 1.28 for polyisoprene. Subsequently, Grubbs and coworkers [273] used this alkoxyamine and successfully controlled the radical polymerization of n-butyl acylate at 125°C. Lower ratio of M /M was observed when the alkoxyamine was preheated at temperatures up to 125 for 30 mm prior to adding the monomer. This prereaction was needed for an excess of free nitroxide to be formed in situ and for polymerization to be controlled. 

The concentration of heavy metal ions that results in fat (oil) shelf-life instability is dependent on the nature of the metal ion and the fatty acid composition of the fat (oil). Edible oils of the linoleic acid type, such as sunflower and com germ oil, should contain less than 0.03 ppm Fe and 0.01 ppm Cu to maintain their stability. The concentration limit is 0.2 ppm for Cu and 2 ppm for Fe in fat with a high content of oleic and/or stearic acids, e. g. butter. Heavy metal ions trigger the autoxidation of unsaturated acyl lipids only when they contain hydroperoxides. That is, the presence of a hydroperoxide group is a prerequisite for metal ion activity, which leads to decomposition of the hydroperoxide group into a free radical ... 

---