Time-Resolved Spectroscopic Study of N,N–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.

The Physical Chemistry and Chemical Physics (PCCP) Section of the International Journal of Molecular Sciences in Its Publications: The First 300 Thematic Articles in the First 3 Years

“…This area is the largest in terms of the number of related publications and includes 91 articles, namely [ 1 , 2 , 3 , 102 , 103 , 104 , 105 , 106 , 107 , 108 , 109 , 110 , 111 , 112 , 113 , 114 , 115 , 116 , 117 , 118 , 119 , 120 , 121 , 122 , 123 , 124 , 125 , 126 , 127 , 128 , 129 , 130 , 131 , 132 , 133 , 134 , 135 , 136 , 137 , 138 , 139 , 140 , 141 , 142 , 143 , 144 , 145 , 146 , 147 , 148 , 149 , 150 , 151 , 152 , 153 ,…”

“…The last one seems to be the most detailed, and it is precisely this that we will try to implement in the course of our narrative. As it should be expected, a priori, most of the publications in this direction are devoted to organic compounds, and primarily organic molecules; these include, with varying degrees of correctness, publications [ 1 , 2 , 3 , 102 , 103 , 104 , 106 , 108 , 112 , 117 , 118 , 119 , 121 , 124 , 127 , 128 , 130 , 131 , 132 , 133 , 135 , 138 , 139 , 140 , 141 , 142 , 143 , 144 , 146 , 147 , 148 , 151 , 153 , 154 , 156 , 157 , 164 , 165 , 166 , 168 , 171 , 172 , 174 , 176 , 178 , 180 , 183 , 185 , 186 ]. Much less space is occupied by the works related to polymeric (in fact, to a high molecular weight) compounds [ 113 , …”

“…There are practically no works on the structure/dynamics of synthetic polymers in the list of these 300 publications; the only exception, and even then with a stretch, that can be considered is article [ 177 ], in which polyurethane fibers are one of the objects of research. In fact, in this list, there are no articles in which the object of study would be ions, free radicals, and clusters, although, with a certain stretch, they can be attributed to them [ 118 , 155 , 169 ], in particular, publication [ 118 ] devoted to the N,N–di(4–Bromo)nitrenium. Be that as it may, the objects in these articles are distinguished by an exceptional variety, and it is extremely difficult, if not impossible, to carry out a more detailed systematization of them (and even more so, to give details of their content in this review article).…”

“…In [ 107 ], this object was methane hydrate; in [ 111 ], a Cu(II) complex with polyvinyl alcohol; in [ 170 ], a heteronuclear complex of Cu(II) and Cd(II) with a “cubane” core; and in [ 175 ], Co(III) with ammonia or 1,10-phenanthroline. The articles [ 118 , 184 ] should be noted among the works devoted to inorganic ions. In the first of them, as it was already mentioned earlier, the structure of the N , N –di(4–bromo) nitrenium ion was considered, and, in the second, the processes of chemisorption of s-element ions of group I in the periodic table with thiacalix[4]arene mono crown.…”

Generation ofN,N-Di(4-bromophenyl)nitrenium Ion under Acidic Conditions: Search for a Nitrenium Dication

“…The latter observation raises the possibility that the long-lived 720 nm species might be the dication. In fact, several transient Raman peaks detected in this process are consistent with the theoretically predicted spectrum for the dication …”