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_2PC_6H_4)_3Si−) toward organoazides has been examined. 1-Adamantylazide was found to coordinate the iron center to form stable [SiP^(iPr)_3]Fe(η^1-N_3Ad). Aryl azides instead afforded unstable [SiP^(iPr)_3]Fe(N_3Ar) species that decayed gradually to regenerate [SiP^(iPr)_3]Fe(N_2) with release of azoarenes (ArN═NAr). 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_3Ar) in a frozen glass. The electronic structures of these putative nitrene intermediates have been examined by DFT methods.

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