Computational, Mechanistic, and Experimental Insights into Regioselective Catalytic C–C Bond Activation in Linear 1‑Aza-[3]triphenylene

C–C bond activation
by transition metal complexes in ring-strained
compounds followed by annulation with unsaturated compounds is an
efficient approach to generate structurally more complex compounds.
However, the site of catalytic C–C bond activation is difficult
to predict in unsymmetrically substituted polycyclic systems. Here,
we report a study on the (regio)­selective catalytic cleavage of selected
C–C bonds in 1-aza-[3]­triphenylene, followed by annulation
with alkynes, forming products with extended π-conjugated frameworks.
Based on density functional theory (DFT) calculations, we established
the stability of possible transition metal intermediates formed by
oxidative addition to the C–C bond and thus identified the
likely site of C–C bond activation. The computationally predicted
selectivity was confirmed by the following experimental tests for
the corresponding Ir-catalyzed C–C cleavage reaction followed
by an alkyne insertion that yielded mixtures of two mono-insertion
products isolated with yields of 34–36%, due to the close reactivity
of two bonds during the first C–C bond activation. Similar
results were obtained for twofold Ir- or Rh-catalyzed insertion reactions,
with higher yields of 72–77%. In a broader context, by combining
DFT calculations, which provided insights into the relative reactivity
of individual C–C bonds, with experimental results, our approach
allows us to synthesize previously unknown pentacyclic azaaromatic
compounds.

过渡金属配合物介导的环张力化合物中碳-碳键（C–C bond）活化，随后与不饱和化合物发生环化反应，是制备结构更复杂化合物的高效途径。然而，在不对称取代的多环体系中，催化碳-碳键活化的位点难以预测。本文针对1-氮杂-[3]-三联苯（1-aza-[3]-triphenylene）中特定碳-碳键的（区域）选择性催化断裂展开研究，随后将产物与炔烃进行环化，得到具有延展π共轭骨架的目标产物。基于密度泛函理论（DFT）计算，我们对通过氧化加成过程与碳-碳键结合形成的各类过渡金属中间体的稳定性进行了分析，由此确定了碳-碳键活化的潜在位点。计算预测的选择性通过后续实验得到验证：针对相应的铱（Ir）催化碳-碳键断裂并随后发生炔烃插入的反应，由于初始碳-碳键活化阶段两个键的反应活性相近，最终得到两种单插入产物的混合物，分离产率为34%~36%。对于两轮铱或铑（Rh）催化的插入反应，我们得到了类似结果，目标产物产率提升至72%~77%。从更广泛的研究视角来看，结合可揭示各碳-碳键相对反应活性的密度泛函理论计算与实验结果，本研究策略可用于合成此前尚未被报道的五环氮杂芳香族化合物。