Synthesis of Coordinatively Unsaturated Iron Complexes and C-H Bond Activation

C-H键的活化是金属有机反应的关键基础步骤，在有机合成中具有重要的应用价值。由于在温和的条件下成功激活C-H键需要制备配位不饱和配合物，因此我们合成了N-杂环卡宾的配位不饱和半夹心铁配合物。研究发现，铁络合物与噻吩类、呋喃类、苯并噻吩类、苯并呋喃类或吡啶类化合物处理后，再加入氢化硼烷，即可发生顺序的C-H键活化和硼化反应。基于这些化学计量反应的研究结果，我们开发了甲基取代的N-杂环卡宾的半三明治铁配合物催化呋喃和噻吩类化合物的C-H键活化/硼化反应。我们还对新的铁络合物进行了一系列反应，以获得接近化学计量比的底物，以获得机理上的见解。

The activation of C-H bonds is a key elementary step of organometallic reactions, and has great utility in organic synthesis. As a requirement for successful C-H bond activation under mild conditions would be preparation of coordinatively unsaturated complexes, we have synthesized coordinatively unsaturated half-sandwich iron complexes of N-heterocyclic carbenes. The sequential C-H bond activation and borylation reactions were found to occur upon treatment of the iron complexes with thiophene, furan, benzothiophene, benzofuran, or pyridine, followed by addition of hydroboranes. Based on these findings on stoichiometric reactions, we have developed the catalytic C-H bond activation/borylation of furans and thiophenes mediated by a half-sandwich iron complex of the methyl-substituted N-heterocyclic carbene. We have also conducted a series of reactions of the new iron complexes with nearly stoichiometric amount of substrate, to gain mechanistic insights.