Reaction of the 4-Biphenylnitrenium Ion with 4-Biphenyl Azide to Produce a 4,4′-Azobisbiphenyl Stable Product: A Time-Resolved Resonance Raman and Density Functional Theory Study

A time-resolved resonance Raman (TR³) and density functional theory (DFT) study of the reaction of the 4-biphenylnitrenium ion with 4-biphenyl azide in a mixed aqueous solution is reported. The reaction of the 4-biphenylnitrenium ion with its unphotolyzed precursor 4-biphenyl azide in a mixed aqueous solution generates a 4,4′-azobisbiphenyl stable product via an intermediate species. With the aid of DFT calculations for likely transient species, this intermediate was tentatively assigned to a 4,4′-azobisbiphenyl cation. The DFT calculations predict this reaction can take place via two pathways that compete with one another to produce the trans and cis 4,4′-azobisbiphenyl product. The observation of the 4,4′-azobisbiphenyl cation intermediate demonstrates that the reaction of the arylnitrenium ion with its aryl azide to produce a stable azo product occurs via a stepwise mechanism.