Photolysis of bis(diisopropylamino)- and bis(dicyclohexylamino)phosphanyl azides 1a and 1b with dimesitylfluoroborane leads to P-fluoro-N-boryliminophosphoranes 3a and 3b, in 80% yields; according to an X-ray crystal diffraction study, 3b has a pseudo-aliene structure. Thermolysis of azide 1b with dimesitylmethyl- and dimesitylethylborane affords N-boryl-N-mesityl-N-phosphanylamines 7 and 15 in 85 and 90% yield, respectively. Photolysis of 1a and 1b with triethyl- or tricyclohexylborane gives rise to P-hydrogeno-N-boryliminophosphoranes 8a,b or 9a,b, in good yields, along with ethylene or cyclohexene. It is shown that no interaction occurs between the boranes and the azides used. All the results are rationalized by the transient formation of phosphanylnitrene-borane adducts, possessing a PN multiple bond, which undergo either a 1,2-migration of a boron substituent to the "nitrene" center or a retro-ene type reaction.