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

• Main Authors: Lili Du, Zhiping Yan, Xueqin Bai, Runhui Liang, David Lee Phillips
• Format: Article
• Language: English
• Published: MDPI AG 2019-11-01
• Series: International Journal of Molecular Sciences
• Subjects: nitrenium ion; time resolved spectroscopy; resonance raman
• Online Access: https://www.mdpi.com/1422-0067/20/21/5512

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 <i>N</i>(4,4&#8242;&#8722;dibromodiphenylamino)&#8722;2,4,6&#8722;trimethylpyridinium BF₄^&#8722; salt (<b>1</b>) in an acidic aqueous solution. Efficient cleavage of the N&#8722;N bond (4 ps) to form the <i>N,N</i>&#8722;di(4&#8722;bromophenyl)nitrenium ion (<b>DN</b>) was also observed in the acidic aqueous solution. As a result, the dication intermediate <b>4</b> appears more likely to be produced after abstracting a proton for the nitrenium ion <b>DN</b> in the acid solution first, followed by an electron abstraction to form the radical cation intermediate <b>3</b>. 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.