Iron(II) Active Species in Iron-Bisphosphine Catalyzed Kumada and Suzuki-Miyaura Cross-Couplings of Phenyl Nucleophiles and Secondary Alkyl Halides.
Iron(II) Active Species in Iron-Bisphosphine Catalyzed Kumada and Suzuki-Miyaura Cross-Couplings of Phenyl Nucleophiles and Secondary Alkyl Halides.
复制标题
DOI：
10.1021/jacs.5b06648
复制
发表时间：
2015-09-09
影响因子：
15
通讯作者：
Neidig ML
中科院分区：
文献类型：
--
作者：
Daifuku SL;Kneebone JL;Snyder BE;Neidig ML
虽然先前的研究已经确定FeMes 2（SciCl 2）作为铁-SciCl 2催化的Kumada交叉偶联的均三甲苯基溴化镁和伯烷基卤化物中的活性催化剂物种，但与苯基亲核试剂交叉偶联的活性催化剂物种（其中低价铁物种可能由于可接近的还原消除途径而普遍存在）仍然不确定。在本研究中，原位穆斯堡尔谱和磁性圆二色光谱研究结合无机合成和反应研究，以评估原位形成的铁物种，并确定在铁Sciodine催化Suzuki-Miyaura和Kumada交叉偶联的苯基亲核试剂和仲烷基卤化物的活性催化物种。虽然在FeCl 2（SciCl 2）与苯基亲核试剂反应时发生还原消除以形成Fe（η6-联苯）（SciCl 2），但未发现该铁（0）物质在动力学上具有催化能力。重要的是，单-和双-苯基化的铁（II）-Sciodine物种，形成之前，还原消除被确定，其中两个物种被发现是对亲电体在催化相关的速率反应。在Kumada和Suzuki-Miyaura反应中，结合原位铁物种的金属转移不足性质，观察到的单苯基化物种形成交叉偶联产物的较高选择性表明Fe（Ph）X（Sci）（X = Br，Cl）是交叉偶联中的主要反应物种。总体而言，这些研究表明，低价铁是不需要的高活性物质的有效芳基-烷基交叉偶联的产生。
While previous studies have identified FeMes2(SciOPP) as the active catalyst species in iron–SciOPP catalyzed Kumada cross-coupling of mesitylmagnesium bromide and primary alkyl halides, the active catalyst species in cross-couplings with phenyl nucleophiles, where low valent iron species might be prevalent due to accessible reductive elimination pathways, remains undefined. In the present study, in situ Mössbauer and magnetic circular dichroism spectroscopic studies combined with inorganic syntheses and reaction studies are employed to evaluate the in situ formed iron species and identify the active catalytic species in iron–SciOPP catalyzed Suzuki–Miyaura and Kumada cross-couplings of phenyl nucleophiles and secondary alkyl halides. While reductive elimination to form Fe(η6-biphenyl)(SciOPP) occurs upon reaction of FeCl2(SciOPP) with phenyl nucleophiles, this iron(0) species is not found to be kinetically competent for catalysis. Importantly, mono- and bis-phenylated iron(II)–SciOPP species that form prior to reductive elimination are identified, where both species are found to be reactive toward electrophile at catalytically relevant rates. The higher selectivity toward the formation of cross-coupled product observed for the monophenylated species combined with the undertransmetalated nature of the in situ iron species in both Kumada and Suzuki–Miyaura reactions indicates that Fe(Ph)X(SciOPP) (X = Br, Cl) is the predominant reactive species in cross-coupling. Overall, these studies demonstrate that low-valent iron is not required for the generation of highly reactive species for effective aryl-alkyl cross-couplings.