Sterically encumbered pyrrolyl ligands and their incorporation into the cycloheptatrienyl zirconium coordination sphere
作者:Markus Kreye、Andreas Glöckner、Constantin G. Daniliuc、Matthias Freytag、Peter G. Jones、Matthias Tamm、Marc D. Walter
DOI:10.1039/c2dt32433d
日期:——
An improved synthesis of 2,5-di(tert-butyl)-3,4-dimethylpyrrole (2-H, HPyrtBu2Me2) and a subsequent reaction with KH yield K(PyrtBu2Me2) (2-K) in multi-gram quantities. Four different pyrrolyl (Pyr) and imidazolyl (Im) ligands were used in salt metathesis reactions with [(η7-C7H7)ZrCl(tmeda)] (7) to afford a series of azatrozircenes: [(η7-C7H7)Zr(η5-PyrtBu2)] (1-Zr), [(η7-C7H7)Zr(η5-PyrtBu2Me2)] (2-Zr), [(η7-C7H7)Zr(η5-PyrtBu3)] (3-Zr) and [(η7-C7H7)Zr(η5-ImtBu3)] (4-Zr), which were characterized by NMR spectroscopy and elemental analysis. In addition, the molecular structures of 2-H, 2-K·18-crown-6, 1-Zr, 2-Zr and 4-Zr were determined by X-ray diffraction analysis, revealing η5- rather than κ1-N-coordination of the N-heterocyclic ligands. Cone angle measurements on the sandwich complexes 1-Zr–4-Zr showed that their nitrogen-containing ligands belong to the class of very sterically encumbered π-ligands, but DFT calculations suggest lower stabilities compared to their all-carbon analogues.
通过改进 2,5-二(叔丁基)-3,4-二甲基吡咯(2-H,HPyrtBu2Me2)的合成以及随后与 KH 的反应,得到了多克量的 K(PyrtBu2Me2) (2-K)。四种不同的吡咯(Pyr)和咪唑(Im)配体与[(η7-C7H7)ZrCl(tmeda)] (7)发生了盐偏析反应,生成了一系列氮杂环烯:(η7-C7H7)Zr(η5-PyrtBu2)](1-Zr)、[(η7-C7H7)Zr(η5-PyrtBu2Me2)](2-Zr)、(η7-C7H7)Zr(η5-PyrtBu3)](3-Zr)和[(η7-C7H7)Zr(η5-ImtBu3)](4-Zr),并通过核磁共振光谱和元素分析对它们进行了表征。此外,还通过 X 射线衍射分析确定了 2-H、2-K-18-crown-6、1-Zr、2-Zr 和 4-Zr 的分子结构,揭示了 N-杂环配体的η5-配位而非κ1-N-配位。对夹心配合物 1-Zr-4-Zr 进行的锥角测量表明,它们的含氮配体属于立体性很强的 π 配体,但 DFT 计算表明,与它们的全碳类似物相比,它们的稳定性较低。