The solution structures of the novel heterobimetallic complexes [Ir(dppm)(Ph(2)PCH(2)PPh(2)PPPP){Pt(PPh(3))2}]OTf and [Rh(dppm)(Ph(2)PCH(2)PPh(2)PPPP){Pt(PPh(3))(2)}]OTf derived from the reaction of Rh and Ir--P(5) precursors with [Pt(C2H4)(PPh3)2] have been unambiguously assigned on the basis of 1H NMR and 31P{1H} NMR data. The results are in agreement with the regio-selective insertion of the {Pt(PPh3)2} moiety resulting in a new pentaphosphorus topology which agrees with the formal formation of a unique phosphonium(+)-tetraphosphabutadienide(2-) ligand.