研究室工作進展 Jul. 28th, 2017
Synthesis and Structural Characterization of Butadienylcalcium-based Heavy Grignard Reagents and a Ca4[O] Inverse Crown Ether Complex
Baosheng Wei, Liang Liu, Wen-Xiong Zhang,* and Zhenfeng Xi
Angew. Chem. Int. Ed. 2017, 56, 9188–9192.
In contrast to the prosperity and great use of Grignard reagents in organometallic and synthetic chemistry, heavy Grignard reagents (RAeX, Ae = Ca, Sr, and Ba, X = halides) and the related chemistry are still in their infancy. Current study centers on the synthetic utilities of heavy Grignard reagents generated in situ, in which the reactive species mostly remain elusive because of their inaccessibility and remarkable instability. The structure elucidation of heavy Grignard reagents or corresponding reaction intermediates has been greatly strived after by chemists.
We applied the cooperative stabilizing ability of butadienyl skeletons and successfully synthesized a series of butadienylcalcium compounds, including 1-calcio-4-lithio-1,3-butadiene, 1,4-dicalcio-1,3-butadiene, and a Ca4[O] inverse crown ether complex, via the reaction between 1,4-dilithio-1,3-butadienes and calcium iodide in THF. In particular, the THF molecule was found to be degraded in an unconventional manner by virtue of the synergistic effect of dicalcium reagents, resulting in the novel inverse crown ether complex with the expanded category of bonding anions and metal cations. Single-crystal X-ray analysis of these unprecedented butadienylcalcium compounds revealed unique structural characteristics and bonding modes. This study provides a novel class of alkenyl heavy Grignard reagents and a useful synthetic strategy for otherwise unavailable reactive organometallic compounds.
亮點介紹
格氏試劑是大家熟知的金屬有機試劑，與鎂同族的Ca, Sr, Ba的類似物，稱為重格氏試劑。由于重格氏試劑合成方法有限、穩定性差等特點，一直以來發展極為緩慢。目前的研究主要集中在重格氏試劑的原位反應性和少量穩定類型重格氏試劑的結構表征上，而對于高活性重格氏試劑的合成與表征則充滿挑戰。
本研究室在前期工作中發展了重格氏試劑有價值的合成應用(Angew. Chem. Int. Ed. 2013, 52, 10822–10825; Nat. Commun. 2014, 5, 4508–4517; Organometallics 2016, 35, 1458–1463.)，但沒有分離到體系中的反應中間體，即“丁二烯基重格氏試劑”。在該項工作中，魏保生同學首次利用轉金屬化反應，成功合成、分離了多種丁二烯基重格氏試劑；利用我們合成的丁二烯基雙鈣重格氏試劑，由于兩個鈣的協同反應性和鈣-碳鍵強的離子性，它能撕裂四氫呋喃的兩個C-O鍵，形成[Ca4O]反式冠醚。該工作為反式冠醚的合成與應用提供了一個有效途徑。