Catalytic N-N coupling of aryl azides to yield azoarenes via trigonal bipyramid iron-nitrene intermediates

Abstract

The reactivity of the trigonal bipyramidal iron(I) complex [SiP(iPr)(3)]Fe(N(2)) ([SiP(iPr)(3)] = (2-iPr(2)PC(6)H(4))(3)Si(-)) toward organoazides has been examined. 1-Adamantylazide was found to coordinate the iron center to form stable [SiP(iPr)(3)]Fe(eta(1)-N(3)Ad). Aryl azides instead afforded unstable [SiP(iPr)(3)]Fe(N(3)Ar) species that decayed gradually to regenerate [SiP(iPr)(3)]Fe(N(2)) with release of azoarenes (ArN horizontal lineNAr). The conversion of aryl azides to azoarenes can thus be achieved catalytically. Competitive trapping experiments strongly suggest the intermediacy of reactive nitrene complexes of the type [SiP(iPr)(3)]Fe(NAr) that couple bimolecularly in the N-N bond forming step. Evidence for one such intermediate was provided by electron paramagnetic resonance spectroscopy via photolysis of [SiP(iPr)(3)]Fe(N(3)Ar) in a frozen glass. The electronic structures of these putative nitrene intermediates have been examined by DFT methods.