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.
Highlights
Nitrenium ions are common reactive intermediates with a formal positive charge on nitrogen, which attracts lots of attention due to their biological activities
It has been demonstrated that arylnitrenium ions have shown mutagenic properties as a result of chemical carcinogenesis of aromatic amines [1,2,3,4,5,6,7,8,9]
Falvey and coworkers [10,11,12,13] reported several studies on the chemical and spectroscopic behavior of the N,N–diphenylnitrenium ion formed after photoexcitation of the 1–(N,N–dipheylamino)–2,4,6–triphenylpyridinium ion, and this phenylnitrenium ion was predicted to exhibit ground state singlet properties with some overlap between an unoccupied nitrogen based p-orbital with occupied π-orbitals on the phenyl groups [11,14]
Summary
Nitrenium ions are common reactive intermediates with a formal positive charge on nitrogen, which attracts lots of attention due to their biological activities. Falvey and coworkers [10,11,12,13] reported several studies on the chemical and spectroscopic behavior of the N,N–diphenylnitrenium ion formed after photoexcitation of the 1–(N,N–dipheylamino)–2,4,6–triphenylpyridinium ion (see Scheme S1 in the supporting information), and this phenylnitrenium ion was predicted to exhibit ground state singlet properties with some overlap between an unoccupied nitrogen based p-orbital with occupied π-orbitals on the phenyl groups [11,14]. Thomas and coworkers reported that the N,N–di(4–bromophenyl)nitrenium ion (DN) formed after photoexcitation of the N–(4,4 –dibromodiphenylamino)–2,4,6–trimethylpyridinium BF4salt (1) showed more stability and a much longer lifetime than the unsubstituted N,N–diphenylnitrenium ion, the lifetime of which was 124 μs in neat MeCN solution and 6.57 μs in an aqueous solution [13]. AAccccoorrddiinngg ttoo aa pprreevviioouuss ssttuuddyy bbyy FFaallvveeyy aanndd ccoowwoorrkkeerrss [[1133]],, tthhee DDNN iinn aann aacciiddiicc ssoolluuttiioonn sshhoouulldd bbee aabbllee ttoo aabbssttrraacctt aanneelleeccttrroonn,,ffoolllloowweeddwwitihthaannaabbstsrtaractcitoionnoof faapprortootnontotofofromrmthtehreardaidcaiclaclactaiotnio(nin(tinertmeremdeiadtieat3e) a3s) sahsowshnowinnScihnemSceh1em[1e5]1. Faquurtehoeursmsoorleu,tidoennss.itFyurfuthnecrtmioonreth, edoernysi(tDyFfTu)ncctailocnultahtieoonrys w(DeFreT)alcsaolcuutlialitzioendstoweprreedailcstothuetilnizoerdmtaol Rpraemdaicnt tshpeecntorarmofalthReampoasnsisbpleecitnrtaeormf tehdeipatoesss,iabnledinthteersme reedsiualttess,parnodvitdheesneewresiunlstisgphrtoinvtidoethneewstriuncstiughret ainntdo fithnegestrrpurcintut rinefaonrmd faitniognerfporritnhtoisnefoinrmteramtioendifaotresthoobsseerivnetedrminetdhieaatecsidoibcsaeqruveeoduisnstohleutaicoindsicexaaqmueinoeuds isnolouutirosntsudexya. mined in our study
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