Nitrosoarene complexes

Nitrosating agents, 22 144, 145 Nitrosation, electrophilic, 22 144-152 Nitrosoarene complexes, osmium, 37 254 iV-Nitrosobis(trifluoromethyl) amine, 16 29, 30 )-Nitrosobis(trifluoromethyl) hydroxylamine, 16 46... 

At 120 °C and 1 atm, AH =18 Kcal mol and AS = -30 cal mol K have been calculated [112]. In nonpolar solvents such as decane the reaction does not proceed. The deoxygenation of the nitro group to nitroso is considered to be the rate determining step of the reaction, since the subsequent carbonylation of the nitroso compounds to give the isocyanate derivative is about ten times faster than the one of the nitro compound in the presence of [Rh(CO)2Cl]2 as catalyst [114, 115], a reaction which is accelerated by M0CI5. The mechanism of this reactions is discussed in more detail in Chapter 6 we mention here that side-on rhodium nitrosoarene complexes were proposed as intermediates. However, which really are the coordination modes of the nitrosoarene to rhodium(I) in this system is still a question to be solved. As a matter of fact, the known arylnitroso complexes of mononuclear rhodium(I) complexes have a nitrogen-o-bonded nitroso group [116], and some of them can catalyse the carbonylation of nitrosobenzene to PhNCO[117]. 

Complex (J) was crystallographically characterised in the case of Ar = 3,4-dichlorophenyl and shown to have the structure schematically reported in the scheme. Note that the CO2 molecule formed in the first deoxygenation of the nitro compound has not left the coordination sphere of the metal, but has remained included into a metallacyclic structure. Tliis is the earliest intermediate ever isolated in deoxygenation reactions of nitro compounds, though complexes having the same metallacyclic structure had been earlier obtained by interaction of a nitrosoarene complex with CO2 [106-108, 195]. 

The reaction of PhN02 with 2 or 3 is complex but remarkably facile (3 hours at ambient temperature) (192). Quite respectable yields (40-46%) of [CpM(=0)]2(/u,-0)(/x-NPh) are obtained in addition to some Cp2-M2(CO)6. Nitrosoarenes ArNO give the same products (193), suggesting... 

Ru3(CO)i2 reacts with Ar-BIAN to give Ru(Ar-BIAN)(CO)3, which in turn reacts with nitroarenes to give a Ru(Ar-BIAN)(nitrosoarene)(CO)2 complex (Eq. 11.56) [104]. 

The molybdenum-alkyne complex CpMo(CO)3(CCPh) is converted into 1 to exert its catalytic activity during oxidation of arylamines to nitrosoarenes. ... 

Mansuy, D., P. Beaune, T. Cresteil, C. Bacot, J.C. Chottard, and P. Cans (1978). Formation of complexes between microsomal cytochrome P-450-Fe(II) and nitrosoarenes obtained by oxidation of... 

Formation of carbamates or ureas by carbonylation reactions of nitrosoarenes is not an important reaction. Only in one case has the synthesis of phenylcarbamates been reported to be catalysed by a rhodium complex and the selectivity was very poor (< 33 %) [169]. RhCl(COD)(PhNO) was the best catalyst, but several ruthenium, palladium and platinum complexes were also tested. Since the main product of these reactions was almost always azoxybenzene, they are discussed in Chapter 4. 

The clusters [HFe3(CO)n] and [Fe3(CO)n] react with nitro- and nitrosoarenes by an initial electron-transfer process from the complex to the organic compound [250, 252], The latter complex initially affords the radical anion cluster [Fe3(CO)n] , whose structure has been recently solved by X-ray crystallography [250, 251]. Only after almost all of the dianionic compound has been consumed, does the radical anion start to react with the nitro- or nitroso compound. The reactions are complex and the identity of the products is very sensitive to the reaction conditions [250]. The reaction between [HFe3(CO)u] and PhNO could be interpreted according to the following reaction scheme (Scheme 22) [250] ... 

Isolation of purified arylhydroxylamine products is often complicated by their tendency to undergo further reactions, particularly condensation with nitrosoarene impurities to produce azoxy products (Fig. 5) (60). Arylhydroxylamine compounds with high electron density in the aromatic ring system tend to undergo complex oxidative reactions and polymerization. Purified arylhydroxylamines tend to have a short shelf life, even when stored refrigerated in the dark under an inert gas. 

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