Platinum(II) and palladium(II) metallomacrocycles derived from cationic 4,4′-bipyridinium, 3-aminopyrazinium and 2-aminopyrimidinium ligands
作者:David Schilter、Jack K. Clegg、Margaret M. Harding、Louis M. Rendina
DOI:10.1039/b916579g
日期:——
A series of cationic, ditopic N-donor ligands based on 4,4â²-bipyridine (4,4â²-bipy), 3-aminopyrazine (apyz) and 2-aminopyrimidine (apym), each incorporating two positively-charged N-heterocycles linked by a conformationally-flexible spacer unit, have been synthesised and treated with palladium(II) or platinum(II) precursors [M(2,2â²-bipy)(NO3)2] (M = Pd(II) or Pt(II)) to form highly cationic metallocyclic species. Treatment of 1,6-bis(4,4â²-bipyridinium)hexane nitrate with [M(2,2â²-bipy)(NO3)2] in aqueous solution, followed by the addition of KPF6, resulted in the formation of the [2+2] species [M2(2,2â²-bipy)24,4â²-bipy(CH2)64,4â²-bipy}2](PF6)8. Treatment of [Pd(PhCN)2Cl2] with 1,3-bis(4,4â²-bipyridinium)propane hexafluorophosphate in MeCN afforded [Pd2Cl44,4â²-bipy(CH2)34,4â²-bipy}2](PF6)4. When the cationic apyz or apym ligands were used in aqueous solution, the analogous metallomacrocycles did not form. Instead, deprotonation of the exocyclic amino group occurred upon coordination of the ligand to afford a tetranuclear [4+2] species in the case of platinum(II), with Pt(II)â¯Pt(II) bonding supported by strong UV-vis absorption at λ = 428 nm which was assigned to a metal-metal-to-ligand charge transfer (MMLCT) band. Thus, treatment of 1,6-bis(3-aminopyrazinium)hexane nitrate with [Pt(2,2â²-bipy)(NO3)2], followed by the addition of KPF6, led to the formation of the red species [Pt4(2,2â²-bipy)4apyz(CH2)6apyzâ2H}2](PF6)8. No related products could be identified with palladium(II), consistent with the low propensity for this metal ion to form strong Pd(II)â¯Pd(II) bonding interactions.
一系列基于
4,4'-联吡啶(4,4'-bipy)、3-
氨基吡嗪(apyz)和2-
氨基嘧啶(apym)的阳离子双位N-供体
配体被合成,这些
配体各自包含两个正电荷的N-杂环,由一段构象灵活的间隔单元连接。然后将这些
配体与
钯(II)或
铂(II)前驱体[M(2,2'-bipy)(
NO3)2](M = Pd(II) 或 Pt(II))反应,形成高度阳离子的
金属环状物种。将1,6-双(
4,4'-联吡啶盐)己烷
硝酸盐与[Mn(2,2'-bipy)( )2]在
水溶液中反应,随后加入KPF6,形成了[2+2]物种[Pt2(2,2'-bipy)24,4'-bipy(
CH2)6-4,4'-bipy}2](PF6)8。将[Pd(PhCN)2Cl2]与1,3-双(
4,4'-联吡啶盐)
丙烷六氟磷酸盐在MeCN中反应,得到[Pt2Cl44,4'-bipy( )3-4,4'-bipy}2](PF6)4。当在
水溶液中使用阳离子apyz或apym
配体时,未能形成类似的
金属大环化合物。相反,
配体与
金属配合时,外环
氨基的去质子化发生,从而在
铂(II)的情况下形成了四核的[4+2]物种,Pt(II)~Pt(II)的配位通过在λ = 428 nm处的强紫外-可见吸收谱得以支持,该吸收谱被指认为
金属-
金属-
配体电荷转移(MMLCT)带。因此,将1,6-双(3-
氨基吡嗪盐)己烷
硝酸盐与[Pt(2,2'-bipy)( )2]反应后再加入KPF6,生成了红色物种[Pt4(2,2'-bipy)4apyz( )6apyz–2H}2](PF6)8。未能识别与
钯(II)相关的产品,与该
金属离子形成强的Pd(II)~Pd(II)配位相互作用的倾向较低相一致。