Time-Resolved Spectroscopic Study of <i>N,N</i>–Di(4–bromo)nitrenium Ions in Acidic Aqueous Solution

Abstract

Nitrenium ions are common reactive intermediates with high activities towards some biological nucleophiles. In this paper, we employed femtosecond transient absorption (fs-TA) and nanosecond transient absorption (ns-TA) as well as nanosecond time-resolved resonance Raman (ns-TR3) spectroscopy and density function theory (DFT) calculations to study the spectroscopic properties of the N(4,4′−dibromodiphenylamino)−2,4,6−trimethylpyridinium BF4− salt (1) in an acidic aqueous solution. Efficient cleavage of the N−N bond (4 ps) to form the N,N−di(4−bromophenyl)nitrenium ion (DN) was also observed in the acidic aqueous solution. As a result, the dication intermediate 4 appears more likely to be produced after abstracting a proton for the nitrenium ion DN in the acid solution first, followed by an electron abstraction to form the radical cation intermediate 3. These new and more extensive time-resolved spectroscopic data will be useful to help to develop an improved understanding of the identity, nature, and properties of nitrenium ions involved in reactions under acidic aqueous conditions.

Keywords

• nitrenium ion
• time resolved spectroscopy
• resonance raman