Synthesis of Azolyl Carboximidamides as Ligands for Zn(II) and Cu(II): Application of the Zn(II) Complexes as Catalysts for the Copolymerization of Carbon Dioxide and Epoxides¹

A series of novel S,N-heterocyclic (thiazolyl) substituted carboximidamides 3 and 4 was synthesized in yields up to 82% from specific triazinium salts 1 and primary or secondary amines 2 which additionally bear pyridine or imidazole units. These carboximidamides are used as tailor-made ligands for the complexation of Cu(II) and Zn(II). The coordination behavior of 3 and 4 and the properties of the resulting metal complexes are affected a significant extent especially by the nature of these amine substituents. The most important structural feature of the novel complexes is that the ligation of the metal cations is achieved by a 1,3,5-triazapentadienyl anion system, compare the X-ray structure of the model complex Cu-4d. Analogous Zn(II) complexes 5, 6a, 6b, 6c, 7a, and 7b were obtained from carboximidamides 3, 4a, 4b, 4c, 4d, and 4e after reaction with diethylzinc. Interestingly, these Zn(II) complexes possess an intrinsic activity to catalyze the copolymerization of cyclohexene oxide and carbon dioxide to give polycarbonates 15 (TON up to 113; Turn Over Number: moles of substrate 14 consumed per moles of zinc. Molecular weights: up to 206·103 Da). Contaminations of 15 by polyethers are produced only in remarkably small amounts.一系列新型S,N杂环（噻唑基（thiazolyl））取代的羧亚胺酰胺（carboximidamides）3与4，以特定三嗪鎓盐（triazinium salts）1和同时带有吡啶（pyridine）或咪唑（imidazole）单元的伯、仲胺（amines）2为原料合成，产率最高可达82%。这类羧亚胺酰胺可作为定制配体，用于铜(II)（Cu(II)）与锌(II)（Zn(II)）的配位络合。3与4的配位行为以及所得金属配合物的性能，在很大程度上受这类胺取代基的性质影响，其中尤以取代基的性质影响最为显著。该类新型配合物最关键的结构特征在于，金属阳离子的配位通过1,3,5-三氮戊二烯阴离子体系（1,3,5-triazapentadienyl anion system）实现，可参照模型配合物Cu-4d的X射线晶体结构（X-ray structure）。将羧亚胺酰胺3、4a、4b、4c、4d与4e分别与二乙基锌（diethylzinc）反应，可得到对应的锌(II)配合物5、6a、6b、6c、7a及7b。值得注意的是，这类锌(II)配合物具有催化环氧环己烷（cyclohexene oxide）与二氧化碳（carbon dioxide）共聚生成聚碳酸酯（polycarbonates）15的本征活性：其转化数（TON, Turn Over Number）可达113，即每摩尔锌对应消耗的底物14的摩尔数；产物分子量最高可达206×10³ Da。聚醚类杂质在产物15中的残留量极低。