Dipartimento di Chimica Inorganica, Chimica Analitica e Chimica Fisica, Università di Messina, Via Sperone 31, 98166 Messina, Italy.
Inorg Chem. 2009 Nov 2;48(21):10397-404. doi: 10.1021/ic900875b.
The equilibrium constants relative to HCl exchange between Pt(II)-containing tight contact ion pairs (TCIP) and pyridine have been investigated in chloroform solution at 298 K. The general formulas of the metal species are: {Pt(H(2)-R(2)-dithiooxamide)(2), 2Cl(-)} (a-type compounds; R = methyl (1a), ethyl (2a), n-propyl (3a), iso-propyl (4a), n-butyl (5a), cyclohexyl (6a), benzyl (7a), beta-phenyl-ethyl (8a), allyl (9a)) and {(H-R(2)-dithiooxamidate)Pt(H(2)-R(2)-dithiooxamide), Cl(-)} (b-type compounds; R has the same meanings as before, given rise to 1b-9b species; moreover, the mixed R compound 10b, containing R = benzyl on a DTO (dthiooxamidate/dithiooxamide) ligand and R = ethyl on the other DTO ligand, has also been investigated). Moreover, the parent species [Pt(H-R(2)-dithiooxamidate)(2)] (c-type compounds; 1c-10c) have also been prepared. Out of 29 compounds reported in the paper, 19 compounds are here reported for the first time, and their synthesis and characterization data are also given. Compounds of a-type exhibit two successive equilibrium constants, which are related to successive HCl transfer from the TCIP to pyridine. By comparing the equilibrium constants Kc of the various b-type species, we have been able to (i) obtain information on the relative stability of the TCIP and, by taking advantage of the two equilibrium constants Kc1 and Kc2 found for each a-type species, (ii) gain knowledge on the electronic interaction between the two basic sites of the Pt(II) bis-dithiooxamide complexes, mediated by the metal center. Linear relationships are found between the pKc of the compounds and the sigma-Taft value (Sigma sigma*) of the amine substituents of the DTO ligands. Interestingly, the slope of such linear correlations is much steeper for pKc2 than for pKc1, indicating that the electronic interaction between the basic sites increases with the electron donating ability of the R substituent. A parallel is proposed between the splitting of HCl transfer equilibrium constants in a-type TCIP and oxidation potential splitting in dinuclear, bridge-linked metal complexes.
在 298 K 的氯仿溶液中，研究了含 Pt(II)的紧密接触离子对 (TCIP) 与吡啶之间相对于 HCl 交换的平衡常数。金属物种的一般公式为：{Pt(H(2)-R(2)-二硫代氧酰胺)(2), 2Cl(-)}（a 型化合物；R = 甲基（1a）、乙基（2a）、正丙基（3a）、异丙基（4a）、正丁基（5a）、环己基（6a）、苄基（7a）、β-苯乙基（8a）、烯丙基（9a））和{(H-R(2)-二硫代氧酰胺)Pt(H(2)-R(2)-二硫代氧酰胺), Cl(-)}（b 型化合物；R 具有与前文相同的含义，产生了 1b-9b 物种；此外，还研究了含有 R = 苄基的 DTO（二硫代氧酰胺/二硫代氧酰胺）配体和 R = 乙基的另一个 DTO 配体的混合 R 化合物 10b）。此外，还制备了母体物种 [Pt(H-R(2)-二硫代氧酰胺)(2)]（c 型化合物；1c-10c）。本文报道的 29 种化合物中，有 19 种是首次报道，同时给出了它们的合成和表征数据。a 型化合物表现出两个连续的平衡常数，这与 TCIP 中 HCl 的连续转移有关。通过比较各种 b 型物种的平衡常数 Kc，我们能够（i）获得有关 TCIP 相对稳定性的信息，并且利用每个 a 型物种发现的两个平衡常数 Kc1 和 Kc2，（ii）了解 Pt(II)双二硫代氧酰胺配合物两个碱性位点之间的电子相互作用，这种电子相互作用通过金属中心进行介导。发现化合物的 pKc 与 DTO 配体的胺取代基的 Taft 值（Sigma sigma*）之间存在线性关系。有趣的是，pKc2 的斜率比 pKc1 陡峭得多，这表明碱性位点之间的电子相互作用随着 R 取代基的供电子能力的增加而增加。在 a 型 TCIP 中 HCl 转移平衡常数的分裂与桥连金属配合物中二核氧化电势的分裂之间提出了一种类比。
