Manganese electrophilic addition with

The vinyl derivative was converted to ethynyl-CTM by reaction with bromine followed by HBr elimination. The double bond of vinyl-CTM turned out to be much less active than that in the ferrocene analog as regards electrophilic addition. Also, the stabilization of an a-carbonium center, the phenomenon characteristic of ferrocenyl cation, was not found in the manganese compound (379). 

These reactions, shown in Table VII, are chiefly a special type of oxidative addition process. Most important are those involving insertion of "Fe(CO)4 this is thought to occur via electrophilic Si-C cleavage in an essentially concerted process. Experiments with substituted silacyclobutanes have shown that the process is both regio- and stereospecific (135). Other metals seem reluctant to undergo this reaction the manganese analog in entry 23 is thermally very unstable. 

Enolate Alkylations with Transition Metal Coordinated Electrophiles. Coordination of various transition metals to dienes and aromatic compounds sufficiently activates these compounds to nucleophilic addition, resulting in high asymmetric induction at the a-center. However, the manganese complexes of various benzene derivatives couple with lithium enolates in low selectivity at the nascent stereogenic center on the ring (eq 15). ... 

Vanhoye and coworkers [402] synthesized aldehydes by using the electrogenerated radical anion of iron pentacarbonyl to reduce iodoethane and benzyl bromide in the presence of carbon monoxide. Esters can be prepared catalytically from alkyl halides and alcohols in the presence of iron pentacarbonyl [403]. Yoshida and coworkers reduced mixtures of organic halides and iron pentacarbonyl and then introduced an electrophile to obtain carbonyl compounds [404] and converted alkyl halides into aldehydes by using iron pentacarbonyl as a catalyst [405,406]. Finally, a review by Torii [407] provides references to additional papers that deal with catalytic processes involving complexes of nickel, cobalt, iron, palladium, rhodium, platinum, chromium, molybdenum, tungsten, manganese, rhenium, tin, lead, zinc, mercury, and titanium. 

Manganese(III) can oxidize carbonyl compounds and nitroalkanes to carboxy-methyl and nitromethyl radicals [186]. With Mn(III) as mediator, a tandem reaction consisting of an intermolecular radical addition followed by an intramolecular electrophilic aromatic substitution can be accomplished [186, 187). Further Mn(III)-mediated anodic additions of 1,3-dicarbonyl and l-keto-3-nitroalkyl compounds to alkenes and alkynes are reported in [110, 111, 188). Sorbic acid precursors have been obtained in larger scale and high current efficiency by a Mn(III)-mediated oxidation of acetic acid acetic anhydride in the presence of butadiene [189]. Also the nitromethylation of benzene can be performed in 78% yield with Mn(III) as electrocatalyst [190]. A N03 radical, generated by oxidation of a nitrate anion, can induce the 1,4-addition of aldehydes to activated olefins. NOj abstracts a hydrogen from the aldehyde to form an acyl radical, which undergoes addition to the olefin to afford a 1,4-diketone in 34-58% yield [191]. 

The benzylic manganese phosphates were also found to react with other electrophiles including aldehydes and ketones. The results are summarized in Table 8.14. Addition to aldehydes gave the corresponding secondary alcohols in moderate yield (38-76%). However, the addition reaction to acetophenone afforded the tertiary alcohol in low yield (19%). The reaction tolerated a nitrile group in the aldehyde (Table 8.14, entry 8) but not a nitro group. When p-cyanobenzyl diethyl phosphate was treated with Mn, only the homocoupled product was observed under a wide range of reaction conditions. 

To expand the range of phosphates for preparation of organomanganese phosphates, alkyl-, phenyl-, and allyl diethyl-phosphates were attempted. Unfortunately, the oxidative addition of active manganese (Mn ) to these phosphates and the subsequent coupling reactions with electrophiles foiled to give the corresponding cross-coupled products. 

---