Nitro arenes, carbonylation

Recently, it has been demonstrated that this anion is the active species in the reduction of the carbon-nitrogen triple bond in acetonitrile10 and it is proposed to be a key intermediate in the reduction of nitro arenes with triiron dodeca-carbonyl.11... 

The carbonylation of nitro arenes can lead to amines, isocyanates, carbamates, azo compounds, or ureas.80 Iron, ruthenium, rhodium, or palladium complexes have been used as catalysts. The carbonylation to give isocyanates, for example, involves the steps... 

Although in all of Geoffroy s papers it was always remarked that no firm evidence existed that the reactions reported were of any relevance to the actual catalytic cycle, this prudent statement is not always found in other authors papers and seems anyway to have been overlooked by many readers, so that the involvement of imido clusters as intermediates in the catalytic carbonylation reactions of nitro-arenes catalyzed by Ru3(CO)i2 seems now to be taken for granted by many researchers in the field. 

Other isocyanate syntheses that have recently been reported include several well-known reactions. One area which has attracted considerable attention is that of the direct production of isocyanates by the carbonylation of nitro-arenes. Both mono- and di-isocyanates are claimed to have been produced using various catalysts palladium, rhodium, and iron compounds often being cited. Other preparative reactions for isocyanates which have appeared in the literature include the acid catalysed hydrolysis of isocyanide dihalides and the reaction between alkyl halides and alkali-metal cyanates, although the latter has been given a modern flavour by the use of a polymer-supported reagent. ... 

Various polycyclic aromatic hydrocarbons, carbonyl arenas, polycyclic nitro-aromatics, aza arenes, N-nitroso compounds, and other carcinogens have been detected in ambient air (Hughes et al, 1980 Kneip et al, 1983 Spiegelhalder and Preussman, 1983). Diesel exhaust particles... 

As with cyclopentadienyl metal carbonyls, the coordination of the net donor arene ligand trans to three 7i-acidic CO ligands confers considerable thermodynamic stability. Relative to the free arene, the coordination of a Cr(CO)3 unit to an arene face removes electron density, to an extent comparable to the inclusion of a nitro ring substituent. The chemical implications of this electron drift from the arene to chromium, and the basis for much chemistry, are an increase in the acidity of protons bound to the arene ring or to the a- and P-carbons of substituents, and... 

Quinone methides are frequently reported as intermediates from irradiation of arenes having a methyl or substituted methyl group in the 2-position to a carbonyl or nitro group (H-abstraction) or a hydroxy function (formal loss of water). The latter process has been studied with pyridoxine (201) and its derivatives (202) and (203), and the mechanism by which the loss occurs is found to depend upon the pH of the solution. In neutral solution, the formation of the quinone methide (204) from (201) arises either by excited state proton transfer to the aqueous methanol solvent and loss of OH from the phenoxide ion, or by intramolecular proton transfer and loss of water, while the reaction in alkaline solution involves dehydroxylation from the excited state of the phenoxide ion. 

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