1,3-Phosphaazaallenes are heteroallenes of the type RP-C-NR′ and little is known about their reactivity. In here we describe the straightforward synthesis of ArPCNR (Ar = Mes*, 2,4,6-tBu-C6H2;MesTer, 2.6-(2,4,6-Me3C6H2)-C6H3;DipTer, 2.6-(2,6-iPr2C6H2)-C6H3; R =tBu; Xyl, 2,6-Me2C6H3) starting from phospha-Wittig reagents ArPPMe3and isonitriles CNR. It is further shown that ArPCNtBu are thermally labile with respect to the loss of iso-butene and it is shown that the cyanophosphines ArP(H)CN are

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... nthetically feasible and form the corresponding phosphanitrilium borates with B(C6F5)3, whereas deprotonation ofDipTerP(H)CN was shown to give an isolable cyanidophosphide. Lastly, the reactivity of ArPCNR towards Pier's borane was investigated, showing hydroboration of the C-N bond in Mes*PCNtBu to give a hetero-butadiene, while withDipTerPCNXyl the formation of the Lewis acid-base adduct with a B-P linkage was observed. © The Royal Society of Chemistry 2021.