The Uracil C(5) Position as a Metal Binding Site: Solution and X-ray Crystal Structure Studies of Pt^II and Hg^II Compounds

1,3-Dimethyluracil (1,3-DimeU) reacts with trans-[(CH₃NH₂)₂Pt(H₂O) ₂]⁺ to give rranH(CH3NH2)2Pt(l,3-DimeUC5)(H₂O)]X (X = NO₃^-, 1a, ClO₄^-, 1b) and subsequently with NaCl to give trans-(CH₃NH₂)₂Pt(1,3-DimeU-C5)Cl (2) or with NH₃ to yield trans-[(CH₃NH₂)₂Pt(1,3-DimeU-C5)(NH ₃)]ClO₄ (3). In a similar way, (dien)Pt^II forms [dienPt(1,3-DimeU-C5)]⁺ (4). Reactions leading to formation of 1 and 4 are slow, taking days. In contrast, Hg(CH₃COO)₂ reacts fast with 1,3-DimeU to give (1,3-DimeU-C5)Hg(CH₃COO) (5). Both 1-methyluracil (1-MeUH) and uridine (urdH) react with (dien)Pt^II initially at N(3) and subsequently with either (dien)Pt^II or Hg(CH₃-COO)₂ also at C(5) to give the diplatinated species 7 and 9 or the mixed PtHg complex 8. C(5) binding of either Pt^II or Hg^II is evident from coupling of uracil-H(6) with either ¹⁹⁵Pt or ¹⁹⁹Hg nuclei and ³J values of 47-74 Hz (for Pt compounds) and 185-197 Hz (for Hg compounds). J values of Pt compounds are influenced both by the ligands trans to the uracil C(5) position and by the number of metal entities bound to a uracil ring. Both 2 and 5 were X-ray structurally characterized. 2: monoclinic system, space group P2_1/c, a = 15.736(6) Å, b = 11.481-(6) Å, c = 25.655 (10) Å, β= 145.55(3)°, V= 2621.9(28) Å3, Z = 4. 5: monoclinic system, space group P2_1/c, a = 4.905(2) Å, b = 18.451(6) Å, c = 11.801(5) Å, β= 94.47(3)°, V = 1064.77(72) ų, Z=4.