Coligand effects on bonding mode. Synthesis and properties of (Diallylmalonato)platinum(II) complexes of P vs. N donating ligand

The reaction of cis-[Pt(II)(OH)₂A₂] (A = triethylphosphine (PEt₃); A₂ = tetrahydro-4H-pyran-4,4-dimethanamine (hpda)) with diallylmalonic acid in aqueous solution affords cis-[Pt(dam)A₂] (dam = diallylmalonate). The bonding mode of the dam is dependent upon the donation effect of the phosphine vs the nitrogen coligand. The crystal structure of cis- [Pt(dam)(PEt₃)₂] (C₂₁H₄₀O₄P₂Pt·H₂O: monoclinic P2₁/c, a = 13.918(2), b = 12.464(1), c = 15.737(1) Å, β = 107.097(8)°, V = 2609.4(4) ų, Z = 4, R = 0.033) discloses that the dam is bonded to the platinum atom in a (χ² O₃)-mode (Pt-O = 2.057(4), 2.061(4) Å) with two phosphine ligands in the cis position. In contrast, for cis-[Pt(dam)(hpda)] (C₁₆H₁₆N₂O₅Pt·4.5H₂O: monoclinic C2/c, a = 28.250(3), b = 11.169(1), c = 13.368(4) Å, β = 94.16(1)°, V = 4207(1) ų, Z = 8, R = 0.0293), the dam ligand is chelated to the platinum(II) ion in a (χO, η²-C,C)-mode (Pt- O = 2.004(4) Å; Pt-C = 2.089(6), 2.101(6) Å) in the solid state. cis- [Pt(χ²O₃-dam)(PEt₃)₂] easily reacts with KBr pellet matrix for IR measurements while cis-[Pt(χO, η²-C,C-dam)(hpda)] is inert in the pellet. In solution, however, the structure of cis-[Pt(χO₃-dam)(PEt₃)₂] is locked, whereas cis-[Pt(χO, η²-C,C-dam)(hpda)] can be isomerized to cis- [Pt(χ²O₃-dam)(hpda)].