Using different organomercury substrates, two isomeric cycloaurated complexes derived from the stabilised iminophosphorane Ph₃P NC(O)Ph were prepared. Reaction of Ph₃P NC(O)Ph with PhCH₂Mn(CO)₅ gave the manganated precursor (CO)₄Mn(2-C₆H₄C(O)N PPh₃), metallated on the C(O)Ph substituent, which yielded the organomercury complex ClHg(2-C₆H₄C(O)N PPh₃) by reaction with HgCl₂ in methanol. Transmetallation of the mercurated derivative with Me₄N[AuCl₄] gave the cycloaurated iminophosphorane AuCl₂(2-C₆H₄C(O)N PPh₃) with an exo PPh₃ substituent. The endo isomer AuCl₂(2-C₆H₄Ph₂P NC(O)Ph) [aurated on a PPh₃ ring] was obtained by an independent reaction sequence, involving reaction of the diarylmercury precursor Hg(2-C₆H₄P( NC(O)Ph)Ph₂)₂ [prepared from the known compound Hg(2-C₆H₄PPh₂)₂ and PhC(O)N₃] with Me₄N[AuCl₄]. Both of the isomeric iminophosphorane derivatives were structurally characterised, together with the precursors (2-HgClC₆H₄)C(O)N PPh₃ and (CO)₄Mn(2-C₆H₄C(O)N PPh₃). The utility of ³¹P NMR spectroscopy in monitoring reaction chemistry in this system is described.