Ligand Influence over the Formation of Dinuclear [2+2] versus Trinuclear [3+3] CuI Schiff Base Macrocyclic Complexes

The preparation and characterization of three new macrocyclic ligands with pendant arms based on the [2+2] condensation of isophthalaldehyde and the corresponding triamine substituted at the central N-atom is reported. None of these new macrocyclic ligands undergo any equilibrium reaction, based on imine hydrolysis to generate [1+1] macrocyclic formation or higher oligomeric compounds, such as [3+3], [4+4], etc., at least within the time scale of days. This indicates the stability of the newly generated imine bond. In sharp contrast, the reaction of the [2+2] macrocyclic Schiff bases with CuI generates the corresponding dinuclear CuI complexes [Cu2(L1)]2+, 12+; [Cu2(L2)(CH3CN)2]2+, 22+; and [Cu2(L3)(CH3CN)2]2+, 32+, together with their trinuclear CuI homologues [Cu3(L4)]3+, 43+; [Cu3(L5)(CH3CN)3]3+, 53+; and [Cu3(L6)(CH3CN)3]3+, 63+, where the [2+2] ligand has undergone an expansion to the corresponding [3+3] Schiff base that is denoted as L4, L5, or L6. The conditions under which the dinuclear and trinuclear complexes are formed were analyzed in terms of solvent dependence and synthetic pathways. The new complexes are characterized in solution by NMR, UV–vis, and MS spectroscopy and in the solid state by X-ray diffraction analysis and IR spectroscopy. For the particular case of the L2 ligand, MS spectroscopy is also used to monitor the metal assisted transformation where the dinuclear complex 22+ is transformed into the trinuclear complex 53+. The CuI complexes described here, in general, react slowly (within the time scale of days) with molecular oxygen, except for the ones containing the phenolic ligands 22+ and 53+ that react a bit faster.

本文报道了三种基于异酞醛与相应三胺在中心N原子上的取代物进行[2+2]缩合反应的新型大环配体的制备与表征。这些新型大环配体均未发生任何平衡反应，基于亚胺水解生成[1+1]大环结构或更高寡聚化合物，如[3+3]、[4+4]等，至少在数天内未观察到。这表明新生成的亚胺键的稳定性。与此形成鲜明对比的是，[2+2]大环席夫碱与CuI的反应生成了相应的双核CuI配合物[Cu2(L1)]2+，12+；[Cu2(L2)(CH3CN)2]2+，22+；以及[Cu2(L3)(CH3CN)2]2+，32+，同时伴随着其三核CuI同系物[Cu3(L4)]3+，43+；[Cu3(L5)(CH3CN)3]3+，53+；和[Cu3(L6)(CH3CN)3]3+，63+，其中[2+2]配体已扩展至相应的[3+3]席夫碱，分别标记为L4、L5或L6。双核和三核配合物形成的条件从溶剂依赖性和合成途径进行了分析。这些新型配合物通过溶液中的核磁共振(NMR)、紫外-可见(UV–vis)和质谱(MS)光谱以及固态中的X射线衍射分析和红外光谱进行了表征。对于L2配体的特殊情况，质谱(MS)还用于监测金属辅助转化，即双核配合物22+转化为三核配合物53+。所描述的CuI配合物通常与分子氧反应缓慢（在数天内），但含有酚配体的22+和53+反应略快。