Thiopyridazine-Based Copper Boratrane Complexes Demonstrating the Z‑type Nature of the Ligand

In Z-type ligands the electrons for the coordination bond are formally provided by the metal. They represent an important addition to the much more extensively used L- and X-type σ-donor ligands for the development of transition metal complexes with new reactivities. We report here a new boron Z-type ligand with three tethering thiopyridazinyl donors forming exclusively complexes that feature a metal boron bond. Rational substitution pattern in the backbone of the pyridazinyl heterocycle led to a well-behaved ligand system that allowed preparation of a series of copper boratrane complexes in high yields. They are found to be more soluble in common organic solvents allowing reactivity studies in contrast to previous complexes with this type of ligand. Thus, copper complexes [Cu­{B­(PnMe,tBu)3}­X] with X = Cl, OTf, N3, and κN-NCS are reported. Solution behavior was explored, and the molecular structures were determined by single-crystal X-ray diffraction analyses. The thiocyanate ligand is found to coordinate via its nitrogen atom pointing to a high oxidation state of the copper. Density functional theory calculations indicate a high positive charge on copper and a strong copper–boron interaction. Thus, here reported complexes deliver synthetic evidence for the Z-type nature of the ligand. These findings are important for further dissemination of these types of ligands in coordination chemistry.

在Z型配体（Z-type ligands）中，配位键所需的电子形式上由金属提供。相较于当前应用更为广泛的L型与X型σ给体配体（L- and X-type σ-donor ligands），此类配体为开发具备新颖反应活性的过渡金属配合物提供了重要的补充类型。本文报道一种新型硼基Z型配体，其带有三个锚定的硫哒嗪基给体单元，可专一性地生成具有金属-硼键（metal boron bond）的配合物。通过对哒嗪杂环（pyridazinyl heterocycle）骨架进行合理的取代基修饰，我们得到了一套性能稳定的配体体系，可高产率制备一系列铜硼杂三环配合物。与此前该类配体所形成的配合物相比，此类配合物在常见有机溶剂中具备更高的溶解度，从而可开展反应活性相关研究。据此，本文报道了X分别为Cl、三氟甲磺酰基（OTf）、叠氮基（N3）以及κN配位模式硫氰酸根（κN-NCS）的铜配合物[Cu{B(PnMe,tBu)3}X]。我们对该类配合物的溶液相行为进行了探究，并通过单晶X射线衍射分析（single-crystal X-ray diffraction analyses）确定了其分子结构。实验发现硫氰酸根配体通过氮原子进行配位，这表明该铜中心处于较高的氧化态。密度泛函理论（Density functional theory）计算结果显示，铜中心带有较高的正电荷，且铜-硼之间存在较强的相互作用。据此，本文所报道的配合物为该配体的Z型配体本质提供了合成实验证据。该研究成果对于推动此类配体在配位化学领域的进一步应用与推广具有重要意义。