Monosubstituted diazenes (NH=NR) are thought to be ubiquitous reactive metabolites responsible (as alkylating agents) for the carcinogenic activity often found in molecules containing the diazo (N-N) functionality. Diimide (NH=NH) and NH=NR species are often invoked as intermediates in a number of important organic reactions (e.g., oxidations of arylhydrazines, Wolff-Kishner reductions, reductive deaminations), but although trans-NH=NR molecules are known, no examples of the cis isomers have been previously detected. This is significant because a trans -> cis isomerization is generally regarded as a key feature in their reaction chemistries. We have developed and recently reported the first method for the clean, stereoselective generation of monosubstituted cis-aryldiazenes (cis-NH=NR). Our technique involves the low-temperature (-5 oC) displacement (by using bromide ions) of the coordinated cis-diazene ligands from easily prepared cationic tungsten complexes, which in turn are prepared by an insertion reaction of aryldiazonium ions into a tungsten hydride bond. A variety of substituted derivatives, including those containing extensive isotopic labels (2H, 15N), can be straightforwardly prepared, thus this unique system is well suited to detailed synthetic, physical, and mechanistic studies of the properties and reactivity modes of these important molecules. The chemistry proposed herein details our plans to: (1) explore the scope of this synthetic method, (2) study the physical properties of this heretofore inaccessible class of molecules, (3) investigate their reaction chemistry, and (4) address fundamental mechanistic details of the nitrogen extrusion and group-transfer (alkylations and arylations) reactions of these molecules.
