N5- in Solution: Isotopic Labeling and Further Details of Its Synthesis by Phenyl Pentazole Reduction.

The cyclopentazolate anion, N5-, has been researched extensively over the years and detected in the gas phase more than a decade ago, but was only recently measured in solution. The process whereby aryl pentazole reduction leads to the production of N5- is still not fully understood. Here, the production of N5- in solution was investigated using isotopic labeling techniques while implementing changes to the synthesis methodologies. 15N labeled phenyl pentazole produced appropriately labeled phenyl pentazole radical anions and N5- which, upon collision induced dissociation, produced the expected N3- signals. Changing to higher purity solvent and less coated Na metal allowed for a much more rapid pace, with experiments taking less time. However, the best yields were obtained with heavily coated metal and much longer reaction times. Utilization of a vacuum line and ultrapure solvents led to no products being detected, indicating the importance of a sodium passivation layer in this reaction and the possibility that sodium is too strong a reducer. These findings can lead to better production methods of N5- and also explain past failures in implementing aryl pentazole reduction techniques.