iClick Reactions of Square-Planar Palladium(II) and Platinum(II) Azido Complexes with Electron-Poor Alkynes: Metal-Dependent Preference for N1 vs N2 Triazolate Coordination and Kinetic Studies with 1H and 19F NMR Spectroscopy,Inorganic Chemistry

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iClick Reactions of Square-Planar Palladium(II) and Platinum(II) Azido Complexes with Electron-Poor Alkynes: Metal-Dependent Preference for N1 vs N2 Triazolate Coordination and Kinetic Studies with 1H and 19F NMR Spectroscopy
Inorganic Chemistry ( IF 4.3 ) Pub Date : 2019-08-08 00:00:00 , DOI: 10.1021/acs.inorgchem.9b01304
Kun Peng ₁ , Viviane Mawamba ₁ , Ellina Schulz ₂ , Mario Löhr ₂ , Carsten Hagemann ₂ , Ulrich Schatzschneider ₁

Affiliation

Two square-planar palladium(II) and platinum(II) azido complexes [M(N₃)(L)] with L = N-phenyl-2-[1-(2-pyridinyl)ethylidene]hydrazine carbothioamide reacted with four different electron-poor alkynes R–C≡C–R′ with R = R′ = COOCH₃, COOEt, COOCH₂CH₂OCH₃ or R = CF₃, R′ = COOEt in a [3 + 2] cycloaddition “iClick” reaction. The resulting triazolate complexes [M(triazolate^R,R’)(L)] were isolated by simple precipitation and/or washing in high purity and good yield. Six out of the eight new compounds feature the triazolate ligand coordinated to the metal center via the N2 nitrogen atom, but fortuitous solubility properties allowed isolation of the N1 isomer in two cases from acetone. When the solvent was changed to DMSO, the N1 → N2 isomerization could be studied by NMR spectroscopy and took several days to complete. ¹⁹F NMR studies of the iClick reaction with F₃C–C≡C–COOEt led to identification of a putative early linear intermediate in addition to the N1 and N2 isomers, however with the latter as the final product. Rate constants determined by ¹H or ¹⁹F NMR spectroscopy increased in the order Pd > Pt and CF₃/COOEt > COOR/COOR with R = CH₃, Et, CH₂CH₂OCH₃. The second-order rate constant k₂ > 3.7 M^–1 s^–1 determined for the reaction of [Pd(N₃)(L)] with F₃C–C≡C–COOEt is the fastest observed for an iClick reaction so far and compares favorably with that of the most evolved strained alkynes reported for the SPAAC (strain-promoted azide–alkyne cycloaddition) to date. Selected title compounds were evaluated for their anticancer activity on the GaMG human glioblastoma brain cancer cell line and gave EC₅₀ values in the low micromolar range (2–16 μM). The potency of the Pd(II) complexes increased with the chain length of the substituents in the 4- and 5-positions of the triazolate ligand.

中文翻译：

方形平面钯（II）和铂（II）叠氮基配合物与电子贫乏炔烃的iClick反应：N1和N2三唑酸酯配位的金属依赖性偏好以及¹ H和¹⁹ F NMR光谱的动力学研究

具有L = N-苯基-2- [1-（2-吡啶基）亚乙基]肼碳硫键的两个方形钯（II）和铂（II）叠氮基络合物[M（N ₃）（L）]与四种不同的碳原子反应贫电子炔烃R–C≡C–R'，在[3 + 2]环加成反应“ iClick”中，R = R'= COOCH ₃，COOEt，COOCH ₂ CH ₂ OCH ₃或R = CF ₃，R'= COOEt反应。所得三唑盐配合物[M（三唑盐^R，R'（L）]通过简单的沉淀和/或洗涤以高纯度和高收率分离。八种新化合物中，六种的特征是三唑盐配体通过N2氮原子与金属中心配位，但是由于偶然的溶解性，在两种情况下都可以从丙酮中分离出N1异构体。当溶剂改为DMSO时，可以通过NMR光谱研究N1→N2异构化，需要几天的时间才能完成。对iClick与F ₃ C–C≡C–COOEt进行的¹⁹ F NMR研究导致除了N1和N2异构体之外，还鉴定出了一种假定的早期线性中间体，但最终的产物是后者。速率常数由¹ H或¹⁹确定F NMR光谱按Pd> Pt和CF ₃ / COOEt> COOR / COOR的顺序增加，其中R = CH ₃，Et，CH ₂ CH ₂ OCH ₃。对于[Pd（N ₃）（L）]与F ₃ C–C≡C–COOEt的反应确定的二级速率常数k ₂ > 3.7 M ^–1 s ^–1是iClick反应最快的观测值，因此到目前为止，与迄今为止报道的SPAAC（应变促进的叠氮化物-炔烃环加成反应）中发展最快的应变炔烃相比，它具有优势。评估选定的标题化合物对GaMG人胶质母细胞瘤脑癌细胞系的抗癌活性，并给出EC ₅₀值在低微摩尔范围（2–16μM）中。Pd（II）配合物的效能随着三唑酸酯配体的4位和5位取代基的链长而增加。

更新日期：2019-08-08

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