Ferrocenyl nitrene

As will be discussed later, it is possible a4> that the thermolysis involves a metal-nitrene complex whereas the photolysis involves the free nitrene. The product distribution is not affected by the presence of a photosensitizer, but since ferrocene itself is both an efficient triplet quencher as well as a sensitizer 26,27) jt is very difficult to probe the spin state of ferrocenyl nitrene at the moment of reaction. The cycli-zation appears to be a singlet reaction since the yield of 27 in benzene solution is essentially unaffected by oxygen or the presence of hydro-quinone a5>. 

Finally, the ferrocenyl complexes were decomposed photochemically and thermally. Thermolyses can be performed in this case because the decomposition temperature of the azide (96) (80 °C) is much lower than those employed for other diazirines and azides. The results obtained from photolyses and thermolyses do not differ significantly. Here again, a-CD causes the most drastic changes because of the complete encapsulation of the guest in a 1 2 complex (Scheme 10.27). In accord with the other reactions performed in a-CD, the main reaction pathway is hydrogen abstraction from the host. Upon thermolysis ferrocenyl amine (112) is obtained in a yield up to 60%. More remailcably, ferrocenyl nitrene (111) seems to react in very low yields with a-CD. However, the structure of the reaction product 113 has not been fully established yet and is quite unexpected because 113 is the result of a glucopyranose-furanose conversion. In contrast, the products obtained by thermolysis of ferrocenyl nitrene in the soUd state, namely... 

Scheme 10.27 Generation of ferrocenyl nitrene (111) and its subsequent reactions...

Other aminoferrocene precursors are Af-ferrocenyl phthalimide, which can be converted to FC-NH2 by N2H4 H2O in boiling ethanol (82% yield) [16, 44], and ferrocenyl azide, FC-N3, which has been reduced with LiAlH4 (72% yield) (cf. Scheme 5-6) [45]. Ferrocenyl amine, FC-NH2, is generally formed among other products in the thermal or photochemical decomposition of FC-N3 [56] and in the thermolysis of ferrocenyl isocyanate, Fc-NCO [57], in solvents such as cyclohexane, cyclohexene and benzene, probably by reaction of the intermediate nitrene, [Fc-N], with the solvent [56, 57]. The reduction of nitroferrocene, FC-NO2, provides another route to aminoferrocene, FC-NH2 [58 — 61] however, FC-NO2 is not an easily accessible starting material. 

The thermal decomposition of ferrocenyl azide in benzene gave ferrocene (13 6%), phenylferrocene (1 9%), azoferrocene (17 8%), and ferroccnylamine (16-9%) Thermolysis of this azide in cyclohexane gave ferrocene (7 3%), and azoferrocene (20 5%). No product of aliphatic G—H insertion nor of aromatic substitution by the nitrene was observed (For more results and a comparison with photolysis, see section V.B.). 

Photolysis of ferrocenylsulfonyl azide (42) in benzene gives the novel ferrocenophane-thiazine-1,1-dioxide (44) as the main product (67%) and some (14%) ferrocenyl sulfonamide (45). No (44) is detected in the corresponding thermal reaction, however, (45) becomes the major product. The multiplicity of the intermediate ferrocenylsulfonyl nitrene (43) has not yet been clarified 565>. 

Trapping of nitrenes by oxygen has been observed in the deoxygenation of nitrosobenzene, thus leading to nitrobenzene. Photolysis of ferrocenyl azide in benzene or cyclohexane under oxygen provides on of the best methods of preparing nitroferrocene ... 

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