One of two PtIV-activated propanenitriles in trans-[PtCl4(EtCN)2] is involved in platinum(IV)-mediated nitrile–imine coupling with the platinum(II)-based metallacycles [PtCl2{NHvC(NR2)N(Ph)C(vNH)N(Ph)- C(NR2)vNH}] [R2 = Me2 (1a), C5H10 (1b)] yielding diplatinum products, whose structures depend on molar ratios between the reactants. At a 1 : 1 ratio, the mixed-valence platinum(II)/platinum(IV) species [PtCl4{NHvC(NR2)N(Ph)C{v[(N(Et)CvNH)PtCl2(EtCN)]}N(Ph)C(NR2)vNH}] [R2 = Me2 (2a), (CH2)5 (2b)] were generated, whereas at a 1 : 2 ratio the dinuclear platinum(II)/platinum(II) complexes [PtCl2{NHv C(NR2)N(Ph)C{v[(N(Et)CvNH)PtCl2(EtCN)]}N(Ph)C(NR2)vNH}] [R2 = Me2 (3a), (CH2)5 (3b)] were obtained. In contrast to the nitrile–imine coupling observed for the platinum(IV) dinitrile complex, the reaction between the platinum(II) congener trans-[PtCl2(EtCN)2] and any one of 1a,b gives exclusively the substituted dimetallic platinum(II)/platinum(II) products [PtCl2{NHvC(NR2)N(Ph)C{v[(NH)PtCl2(EtCN)]}N(Ph)- C(NR2)vNH}] [R