Salen ligands (salen = N,N′-ethylenebis(salicylimine)) are well-known for their versatility and widespread utility in chelating metal complexes. However, installation of hydrogen-bonding units on the salen framework, particularly functional groups that require amine-based precursors such as (thio)ureas, is difficult to achieve without the use of protecting group strategies. In this report, we show that the phenylketone analog of salicyladehyde is a stable alternative that enables the facile installation of hydrogen bonding (thio)urea groups on the salen scaffold, thus imparting anion binding abilities to a metal salen complex. Synthesis of symmetric N-phenyl(thio)urea salen ligands functionalized at the 3,3′-position and an unsymmetric salen ligand with N-phenylurea at the 5-position was achieved. Subsequent metalation with nickel(II) acetate afforded the nickel(II) complexes that were investigated for their anion binding properties towards F⁻, Cl⁻, Br⁻, CH₃COO⁻, and H₂PO₄⁻. Solid-state structures of the nickel(II) complexes as well as the Cl⁻ bound dimer of the symmetric urea complex were obtained. The unusual acidity of the (thio)urea groups is reflected in the pK_a-dependent anion binding behavior of the nickel(II) complexes, as elucidated by ¹H and ¹⁹F Nuclear Magnetic Resonance (NMR) spectroscopy and Diffusion Ordered Spectroscopy (DOSY) experiments.

中文翻译：

---

（硫代）尿素官能化 Ni（II）-salen 配合物的合成和阴离子结合特性


Salen 配体 （salen = N，N′-乙烯双（水杨亚胺）） 以其多功能性和在螯合金属络合物中的广泛用途而闻名。然而，如果不使用保护基团策略，就很难在 salen 框架上安装氢键单元，特别是需要胺基前驱体（如（硫代）尿素）的官能团。在本报告中，我们表明 salicyladehyde 的苯基酮类似物是一种稳定的替代品，它能够轻松地将氢键（硫代）尿素基团安装在 salen 支架上，从而赋予金属 salen 络合物阴离子结合能力。合成了在 3,3' 位官能化的对称 N-苯基（硫代）脲 salen 配体和在 5 位具有 N-苯脲的不对称 salen 配体。随后用乙酸镍 （II） 进行金属化产生了镍 （II） 配合物，研究了其对 F^-、Cl^-、Br^-、CH₃COO^-和 H₂PO₄^-的阴离子结合特性。获得了镍 （II） 配合物的固态结构以及对称尿素配合物的 Cl⁻ 结合二聚体。（硫代）脲基团的异常酸性反映在镍 （II） 配合物的 pK_a 依赖性阴离子结合行为中，如 ¹H 和 ¹⁹F 核磁共振 （NMR） 波谱和扩散有序波谱 （DOSY） 实验所阐明的那样。