Calcium-Catalyzed Arene C-H Bond Activation by Low-Valent AlI
Calcium-Catalyzed Arene C-H Bond Activation by Low-Valent AlI
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DOI：
10.1002/anie.201908978
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发表时间：
2019-09-13
影响因子：
16.6
通讯作者：
Harder, Sjoerd
中科院分区：
文献类型：
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作者：
Brand, Steffen;Elsen, Holger;Harder, Sjoerd
低价SS-DIPP络合物((BDI)-B-DIPP)Al在苯中是稳定的，但在20℃下加入催化量的[(BDI)-B-DIPP](2)得到((BDI)-B-DIPP)Al(Ph)H((BDI)-B-DIPP=CH[C(CH3)N-DIPP](2)，DIPP=2，6-二异丙基苯基)。对于甲苯或对二甲苯，也表现出类似的钙催化的C-H键活化。对甲苯而言，间位官能化具有明显的选择性。((BDI)-B-DIPP)Al(m-甲苯基)H与I-2反应生成间甲苯基碘、H-2和((BDI)-B-DIPP)AlI2，再循环生成((BDI)-B-DIPP)Al。用镁或锌氢化物催化剂催化这一反应的尝试失败了。相反，形成了高度稳定的配合物((BDI)-B-DIPP)Al(H)M((BDI)-B-DIPP)(M=镁，锌)。对氢化钙催化芳烃铝化反应的密度泛函计算表明，形成了一个类似但结合更疏松的络合物：((BDI)-B-DIPP)Al(H)Ca((BDI)-B-DIPP)。这与氢化物桥联络合物((BDI)-B-DIPP)Al(Mu-H)Ca((BDI)-B-DIPP)是平衡的，它显示出强烈的Al电子密度增加。Ca-芳烃键和高度亲核的Al中心的结合是容易激活C-H键的关键。
The low-valent ss-diketiminate complex ((BDI)-B-DIPP)Al is stable in benzene but addition of catalytic quantities of [((BDI)-B-DIPP)CaH](2) at 20 degrees C led to ((BDI)-B-DIPP)Al(Ph)H ((BDI)-B-DIPP=CH[C(CH3)N-DIPP](2), DIPP=2,6-diisopropylphenyl). Similar Ca-catalyzed C-H bond activation is demonstrated for toluene or p-xylene. For toluene a remarkable selectivity for meta-functionalization has been observed. Reaction of ((BDI)-B-DIPP)Al(m-tolyl)H with I-2 gave m-tolyl iodide, H-2 and ((BDI)-B-DIPP)AlI2 which was recycled to ((BDI)-B-DIPP)Al. Attempts to catalyze this reaction with Mg or Zn hydride catalysts failed. Instead, the highly stable complexes ((BDI)-B-DIPP)Al(H)M((BDI)-B-DIPP) (M=Mg, Zn) were formed. DFT calculations on the Ca hydride catalyzed arene alumination suggest that a similar but more loosely bound complex is formed: ((BDI)-B-DIPP)Al(H)Ca((BDI)-B-DIPP). This is in equilibrium with the hydride bridged complex ((BDI)-B-DIPP)Al(mu-H)Ca((BDI)-B-DIPP) which shows strongly increased electron density at Al. The combination of Ca-arene bonding and a highly nucleophilic Al center are key to facile C-H bond activation.