Nitrenium ions 2-fluorenyl

One unusual aspect of these benzidine species is that the dications are less reactive toward solvent than are the monocations. This was not observed for the 2-fluorenyl and 4-biphenylyl nitrenium ions 75g and 75n and their conjugate acids 144g and 144n. The reason for this is not clear, but may be related to the fact that the two positive charges in 144qq and 144rr can be localized onto the two nitrogens on opposite ends of the structures. 

A picosecond Raman spectroscopic examination of the reactions of 2-fluorenyl-nitrene and 4-methoxyphenylnitrene with water revealed singlet nitrenium ions.69 Evidence was presented to suggest that the nitrenes were produced during the photolysis of the corresponding azides. The 4-methoxyphenylnitrene decayed much faster than the 2-fluorenylnitrene. 

McClelland, R. A., Postigo, A., Solvent Effects on the Reactivity of Fluorenyl Nitrenium Ion with DNA like Probes, Biophys. Chem. 2006, 119, 213 218. 

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