Synthesis, structures, and linkage isomerism of (allylbenzylmalonate)platinum(II) complexes

New platinum(II) complexes A₂Pt(ABM) (A = triethylphosphine (TEP); A₂ = 2,2-dimethyl-1,3-propanediamine (DMPDA), trans-(±)-1,2-diaminocyclohexane (DACH); ABM = allylbenzylmalonate) have been synthesized in aqueous solution and characterized by means of X-ray analysis and multinuclear NMR spectroscopy. The crystal structures of cis-(TEP)₂Pt(ABM) (monoclinic P2₁/n, a = 12.179(3), b = 16.869(7), c = 12.870(3) Å, β = 93.27(2)°, V = 2757(1) ų, Z = 4, R = 0.0390) and (DACH)-Pt(ABM)·2H₂O (triclinic P1, a = 7.649(3), b = 14.064(2), c = 19.190(8) Å, α = 98.98(2), β = 90.05(3), γ = 105.73(2)°, V = 1961(1) ų, Z = 2, R = 0.0455) have been solved. The platinum atom in both complexes adopts a typical square planar arrangement with each coligand in cis positions. In the solid state, the ABM ligand exhibits different chelation modes depending on the coligands: (O,O′)-chelation in the phosphine analog and (O,alkene)-chelation in the amine analogs. For the phosphine complex, the (O,O′)-chelation mode of the ABM ligand is impregnable even in solutions at variable temperatures, probably due to the strong π-bonding between the phosphorus and platinum atoms. However, (diamine)platinum(II) complexes have shown interesting linkage isomerism between the (O,O′)- and (O,alkene)-chelation modes in solutions depending on solvent and temperature.