Disilver(I) Rectangular-Shaped Metallacycles: X-ray Crystal Structure and Dynamic Behavior in Solution

Reaction of the ditopic semirigid ligand 1,2-bis(imidazolylmethyl)benzene (1,2-bImb) or the flexible ligand 1,4-bis(2-benzimidazolyl)butane (C4BIm) with AgX (X = ClO4-, BF4-, CF3CO2-) afforded five new complexes, namely, [Ag2(1,2-bImb)2](ClO4)2 (1), [Ag2(1,2-bImb)2](BF4)2 (2), [Ag2(1,2-bImb)2](CF3CO2)2·2CH3OH (3·2CH3OH), [Ag2(C4BIm)2](ClO4)2·2DMF (4·2DMF), and [Ag2(C4BIm)2](CF3CO2)2·2H2O (5·2H2O), all of which contain a centrosymmetric, rectangular-shaped cationic disilver(I) metallacycle [Ag2(L)2]2+. In 1−3, a pair of 1,2-bImb ligands takes on the syn conformation to connect two Ag(I) ions to give a compressed rectangle with a transannular Ag···Ag separation of 3.27−3.36 Å, whereas in 4 and 5, the pair of planar C4BIm ligands acts in the cis conformation to connect two Ag(I) ions to yield a normal rectangle with a transannular Ag···Ag separation of 7.67−7.91 Å. The anions form Ag···O or Ag···F weak interactions in 1−3 and O−H···O or N−H···O hydrogen bonds in 4 and 5 in crystal packing but exhibit no significant influence on the formation of the disilver(I) macrocycles. The solution structure and dynamic behavior of the complexes studied by electrospray ionization mass spectrometry, 1H NMR, and variable-temperature NMR indicated that the dynamic equilibrium between the [Ag2(L)2]2+ cation and the open-ring oligomers or other potential species occurs via solvent-assisted dissociative exchange. The metal−ligand exchange barrier was estimated to be 54.5 kJ mol-1.将双位点半刚性配体1,2-二(咪唑基甲基)苯（1,2-bis(imidazolylmethyl)benzene，缩写1,2-bImb）或柔性配体1,4-二(2-苯并咪唑基)丁烷（1,4-bis(2-benzimidazolyl)butane，缩写C4BIm）与AgX（X=ClO₄⁻、BF₄⁻、三氟乙酸根CF3CO2⁻）进行反应，得到五种新型配合物，分别为：[Ag₂(1,2-bImb)₂](ClO₄)₂（化合物1）、[Ag₂(1,2-bImb)₂](BF₄)₂（化合物2）、[Ag₂(1,2-bImb)₂](CF₃CO₂)₂·2CH₃OH（化合物3·2CH₃OH）、[Ag₂(C4BIm)₂](ClO₄)₂·2DMF（化合物4·2DMF，DMF为N,N-二甲基甲酰胺的缩写）以及[Ag₂(C4BIm)₂](CF₃CO₂)₂·2H₂O（化合物5·2H₂O）。所有配合物均含有一个具有中心对称性的矩形阳离子二银(I)金属环[Ag₂(L)₂]²⁺。在化合物1至3中，一对1,2-bImb配体以syn（同侧）构象与两个Ag(I)离子配位，构建得到一个压缩型矩形金属环，其环内Ag···Ag间距为3.27~3.36 Å；而在化合物4与5中，一对平面型C4BIm配体以cis（顺式）构象连接两个Ag(I)离子，生成标准矩形金属环，环内Ag···Ag间距为7.67~7.91 Å。在晶体堆积过程中，配合物1~3中的阴离子与金属离子形成Ag···O或Ag···F弱相互作用，而配合物4和5中的阴离子则形成O-H···O或N-H···O氢键，但阴离子对二银(I)大环的形成并无显著影响。通过电喷雾电离质谱（ESI-MS）、¹H核磁共振（¹H NMR）及变温核磁共振（VT-NMR）对配合物的溶液结构与动态行为进行表征后发现，[Ag₂(L)₂]²⁺阳离子与开环低聚物或其他潜在物种之间的动态平衡，是通过溶剂辅助解离交换过程实现的。经估算，金属-配体交换的能垒为54.5 kJ·mol⁻¹。