Fakultät Chemie, TU Dortmund, 44221 Dortmund, Germany.
Inorg Chem. 2012 Jun 18;51(12):6784-93. doi: 10.1021/ic3005097. Epub 2012 Jun 4.
Pt(2,2'-bpy)(1-MeC-N3)(2)(2) (1) (2,2'-bpy = 2,2'-bipyridine; 1-MeC = 1-methylcytosine) exists in water in an equilibrium of head-tail and head-head rotamers, with the former exceeding the latter by a factor of ca. 20 at room temperature. Nevertheless, 1 reacts with (en)Pd(II) (en = ethylenediamine) to give preferentially the dinuclear complex Pt(2,2'-bpy)(1-MeC(-)-N3,N4)(2)Pd(en)(2)·5H(2)O (2) with head-head arranged 1-methylctosinato (1-MeC(-)) ligands and Pd being coordinated to two exocyclic N4H(-) positions. Addition of AgNO(3) to a solution of 2 leads to formation of a pentanuclear chain compound {Pt(2,2'-bpy)(1-MeC(-))(2)Pd(en)}(2)Ag(5)·14H(2)O (5) in which Ag(+) cross-links two cations of 2 via the four available O2 sites of the 1-MeC(-) ligands. 2 and 5 appear to be the first X-ray structurally characterized examples of di- and multinuclear complexes derived from a Pt(II) species with two cis-positioned cytosinato ligands adopting a head-head arrangement. (tmeda)Pd(II) (tmeda = N,N,N',N'-tetramethylethylenediamine) and (2,2'-bpy)Pd(II) behave differently toward 1 in that in their derivatives the head-tail orientation of the 1-MeC(-) nucleobases is retained. In Pt(2,2'-bpy)(1-MeC(-))(2){Pd(2,2'-bpy)}(2)(4)·10H(2)O (4), both (2,2'-bpy)Pd(II) entities are pairwise bonded to N4H(-) and O2 sites of the two 1-MeC(-) rings, whereas in Pt(2,2'-bpy)(1-MeC(-))(2){Pd(tmeda)}(2)(NO(3))(3)·5H(2)O (3) only one of the two (tmeda)Pd(II) units is chelated to N4H(-) and O2. The second (tmeda)Pd(II) is monofunctionally attached to a single N4H(-) site. On the basis of these established binding patterns, ways to the formation of mixed Pt/Pd complexes and possible intermediates are proposed. The methylene protons of the en ligand in 2 are special in that they display two multiplets separated by 0.64 ppm in the (1)H NMR spectrum.
Pt(2,2'-bpy)(1-MeC-N3)(2)(2) (1)（2,2'-bpy = 2,2'-联吡啶；1-MeC = 1-甲基胞嘧啶）在水中以头尾和头对头旋转异构体的平衡形式存在，在室温下，前者超过后者约 20 倍。然而，1 与 (en)Pd(II)（en = 乙二胺）反应，优先得到双核配合物Pt(2,2'-bpy)(1-MeC(-)-N3,N4)(2)Pd(en)(2)·5H2O (2)，其中头对头排列的 1-甲基胞嘧啶（1-MeC(-)）配体和 Pd 与两个外环 N4H(-)位置配位。向 2 的溶液中加入 AgNO3 会导致形成五核链状化合物{Pt(2,2'-bpy)(1-MeC(-))(2)Pd(en)}(2)Ag(5)·14H2O (5)，其中 Ag(+) 通过 1-MeC(-)配体的四个可用 O2 位点交叉连接 2 的两个阳离子。2 和 5 似乎是首例 X 射线结构表征的来自具有两个顺式位置胞嘧啶配体的 Pt(II)物种的二核和多核配合物的例子，其采用头对头排列。(tmeda)Pd(II)（tmeda = N,N,N',N'-四甲基乙二胺）和 (2,2'-bpy)Pd(II) 对 1 的行为不同，在它们的衍生物中，1-MeC(-)碱基的头尾取向保持不变。在Pt(2,2'-bpy)(1-MeC(-))(2){Pd(2,2'-bpy)}(2)(4)·10H2O (4)中，两个(2,2'-bpy)Pd(II)实体都成对地与两个 1-MeC(-)环的 N4H(-)和 O2 位点结合，而在Pt(2,2'-bpy)(1-MeC(-))(2){Pd(tmeda)}(2)(NO3))(3)·5H2O (3)中，只有两个(tmeda)Pd(II)单元之一被螯合到 N4H(-)和 O2。第二个(tmeda)Pd(II)单元单核连接到单个 N4H(-)位点。基于这些已建立的结合模式，提出了形成混合 Pt/Pd 配合物和可能的中间体的方法。2 中 en 配体的亚甲基质子很特殊，它们在 (1)H NMR 谱中显示出两个相隔 0.64 ppm 的多重峰。
