Iron, reaction with nitroarenes

Iron, reaction with nitroarenes, 928 lron(lll) bromide, aromatic bromination and, 548 Iron sulfate, LD5q of, 26 Isoamyl group, 89 lsobutane, molecular model of, 80 lsobutyl group, 84... 

In a nitration reaction, aromatic rings react with nitric add in the presence of sulfuric add to yield nitroarenes, which are useful synthetic intermediates because the nitro group can be reduced to an amino group by reaction with H2 and a transition metal catalyst or, alternatively, by using iron, zinc, or tin in HCl followed by base. There is no electrophilic aromatic substitution reaction that introduces the amino group directly onto the aromatic ring. 

The cluster Ru3(CO)i2 is known to react in the presence of bases to afford, under certain experimental conditions, [HRu3(CO)u] [42]. Since the corresponding iron cluster is known to react with nitrobenzene to yield an hydrido imido cluster [HFe3(CO)9(NPh)] , which can be protonated and afford small amounts of aniline [43], a catalytic cycle was proposed, and supported by some model reactions, for the ruthenium-catalysed reduction of nitroarenes by CO/H2O, which includes the intermediate formation of the trinuclear hydrido cluster [44-46]. However, one of us has recently shown that [HFe3(CO)n] and the corresponding imido complex play no role in the Fe3(CO)i2-promoted reduction of nitrobenzene [6, 47] and the proposal of an active role of [HRu3(CO)ii] appears to be questionable. 

For M = Ru, formamides and amines were the principal products. Substitution of Fe3(CO)i2 for Ru3(CO)i2 results in the formation of carbamate esters (ArNHCOOMe) as the major products, with ureas as the main by-products. Without the metal carbonyl, nitroarenes are recovered imchanged from the reaction mixture. An imido-alcoxycarbonyl complex was suggested as an intermediate in the reaction and the difference between iron and ruthenium was proposed to be due to the different facility of this intermediate to undergo protonation and reductive elimination to give carbamate, or insertion of CO into the M-N bond, followed by hydrogenation, affording formamide (Scheme 13) ... 

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