Platinum(II) complexes of 3,3′-disubstituted-2,2′-bipyridines. Synthesis, structures, cytotoxic effect and unusual solvolysis in DMSO

The reaction of 3,3′-disubstituted-2,2′-bipyridines, 2,2′-bipyridyl-3,3′-dicarboxylic acid (H₂BDC) and 3,3′-dimethylol-2,2′-bipyridine (DMB) with potassium tetrachloroplatinate(II) in water gives Pt(H₂BDC)Cl₂ (1) and Pt(DMB)Cl₂ (2), respectively. Both complexes were characterized by elemental analysis and various spectroscopic techniques. The molecular structures of 1 and 2 have been determined by single-crystal X-ray diffraction. 1 · 2DMF: triclinic system, space group P1̄, α = 8.089(9) Å, b = 9.707(8) Å, c = 15.541(4) Å, α = 106.88(6)°, β = 100.41(3)°, γ = 94.39(8)°, V = 1137.8(2) ų, Z = 2. 2: monoclinic system, space group P2₁/c, α = 7.849(5) Å, b = 16.125(3) Å, c = 21.613(5) Å, β = 94.10(2)°, V = 2728.5(9) ų, Z = 8. X-ray structures indicate that two pyridine rings of the bipyridyl ligand in both compounds cannot attain the coplanar state owing to the steric bulkiness of the substituents in the 3,3′-positions. The solvolysis of 1 in DMSO, characterized by ¹H, ¹³C and ¹⁹⁵Pt NMR spectra, leads to the unprecedented example for the complete release of the free amine ligand H₂BDC, yielding the formation of cis-[Pt(Me₂SO)₂Cl₂]. No antitumor activity was observed for 1 and 2 against the leukemia L1210 cell line.