Abstract
N,N′-Diphenyl-3,7-diazacyclooctane and structurally related N,N′-diphenylbispidine derivatives react with silver(I) ions in a high-yielding C–C coupling reaction to produce dication–diradical species, with the silver ions serving a double function both as template and as an oxidant. The resulting bis(benzidino)phane derivatives are persistent organic radicals, stable for several months in solution as well as in the solid state, at room temperature and above, as well as being exposed to the atmosphere. The molecular structure features a double-decker cyclophane motif, stabilized by intramolecular π-dimerization of two delocalized benzidinium radical segments. Intermolecular π-dimers are formed in the solid state.Graphical abstract
Highlights
Persistent organic diradicals are of interest for a variety of applications as functional materials, such as molecular magnets and molecular electronics [1,2,3,4,5,6]
Chemical shifts are reported in ppm referenced to tetramethylsilane via the residual solvent signal (CDCl3, 1H at 7.26 and 13C at 77 ppm; acetone-d6, 1H at 2.05 and 13C at 39.5 ppm). 19F chemical shifts were referenced to external CF2Br2 (7.0 ppm)
The LED– PGSE spectra were evaluated by plotting the square of the gradient strength against the natural logarithm of the signal amplitude, resulting in a straight line with a slope proportional to - D
Summary
Persistent organic diradicals are of interest for a variety of applications as functional materials, such as molecular magnets and molecular electronics [1,2,3,4,5,6]. Diradicals with intramolecular p-p interactions are of particular interest, and only a few examples have been reported [4]. Common structural motifs are based on the dimers of benzidine [7] (4,40–diaminobiphenyl) or N,N,N0,N0-tetraaryl-(1,10-biphenyl)-4,40diamines [8,9,10]. While these usually retain some structural flexibility regarding the p-p-interacting segments, attempts have been made to obtain ‘‘confronted arenes’’ [11] with closer interactions, such as found in cyclophanelike structures [12]. 78 Scheme 1 persistent organic diradicals with strong intramolecular p-p interactions
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