In its co-ordination chemistry P(.dbd6;NAr)(NHAr)(Ar = C6H2Bu^t 3-2,4,6)(1a) behaves either as (i) a source of its conjugate base yielding Ar[graphic ommitted]Ln(2)[MLn= AIMe2, from (AIMe3)2] and (3)(MLn= Li, from LiBuⁿ), or (ii) as a neutral hydrido-P^V ligand in [[graphic ommitted])2PH}], but the arsa(III)azene (1b)[the As analogue of (1a)] undergoes facile Asâ NHAr bond-scission with (AIMe3)2; whereas (1b) is obtained from 2Li(NHAr)+ AsCl3 in OEt2 at 20 °C, prolonged reflux in PhMe of the same reagents furnishes a cyclometallated product; <Pâ N> in (2)[1.617(4)à ] is intermediate between the P.dbd6;N and Pâ N bond lengths in (1a), and is significantly shorter than the 1.74(1)à for <Pâ N> in PAr(NHAr)2[obtained from PArCl2+ 2Li(NHAr)].