Beyond Click-Chemistry: Transformation of Azides with Cyclopentadienyl Ruthenium Complexes

The cyclopentadienyl Ru complexes Cp*RuCl(cod) (cod = 1,5-cyclooctadiene), Cp*RuCl(PPh 3 ) 2, and [Cp ∧ RuCl 2 ] 2 (Cp ∧ = η 5 -1-methoxy-2,4-di- tert -butyl-3-neopentylcyclopentadienyl) are able to catalyze the decomposition of benzyl azides to give 1,3,5-triphenyl-2,4-diazapenta-1,4-diene (“hydrobenzamide”), benzyl-benzylideneamine, and benzonitrile. Reactions with the catalyst precursor [Cp ∧ RuCl 2 ] 2 are particularly fast and give hydrobenzamide with high selectivity. A similar coupling reaction is observed for other benzylic azides but not for (2-azidoethyl)benzene and ethyl-4-azidobutanoate. If the reactions are performed in the presence of water, benzylic azides are converted into aldehydes. Mononuclear tetrazene complexes are formed in stoichiometric reactions of [Cp ∧ RuCl 2 ] 2 with benzyl azide and (2-azidoethyl)benzene.