...
  • 主题
高级搜索  >
历史搜索 清空历史
首页> 外文期刊>Dalton transactions: An international journal of inorganic chemistry >Alkene cyclopropanation catalyzed by Halterman iron porphyrin: participation of organic bases as axial ligands
【24h】

Alkene cyclopropanation catalyzed by Halterman iron porphyrin: participation of organic bases as axial ligands

机译：Halterman铁卟啉催化的烯烃环丙烷化反应：有机碱作为轴向配体的参与

获取原文
获取原文并翻译 | 示例
           
页面导航
  • 摘要
  • 著录项
  • 相似文献
  • 相关主题

摘要

With the iron(III) complex of the Halterman iron porphyrin [P* Fe(Cl)] and ethyl diazoacetate (EDA) as catalyst and carbene source, respectively, styrene-type substrates were converted to cyclopropyl esters with high trans/cis ratio ( not less than 12) and high enantioselectivity for the trans-isomers ( 74 - 86% ee). The isomeric distribution of the cyclopropyl esters so obtained is akin to that obtained from the previously reported Ru(II) counterpart [P* Ru(CO)]. A linear Hammett correlation log(k(X)/k(H)) = sigma(+) rho was observed with rho =- 0.57 suggesting the involvement of an electrophilic cyclopropanating species derived from the iron( II) center as the reactive intermediate in the catalytic cycle. This is further supported by a dramatic decrease in the enantioselectivity and trans/cis ratio observed in an experiment of styrene cyclopropanation when the reaction mixture was deliberately exposed to air. Axial ligand effects on the selectivities was also investigated. Substantial improvement in trans/cis ratios could be achieved by addition of organic bases such as pyridine (py) and 1-methylimidazole (MeIm) to the catalytic reaction. The existence of axially ligated iron carbene moieties, [P* Fe(CHCO2Et)(py)] and [P* Fe(CHCO2Et)(MeIm)], was established by electrospray mass spectrometry. Study of secondary kinetic isotope effect indicated that a more product-like transition state was generated by addition of MeIm.
机译：分别使用Halterman卟啉铁[P * Fe（Cl）]和重氮乙酸乙酯（EDA）的铁（III）络合物作为催化剂和卡宾源，将苯乙烯型底物转化为高反式/顺式比的环丙基酯（不小于12）和高的对映异构体对映体选择性（74-86％ee）。如此获得的环丙基酯的异构体分布类似于从先前报道的Ru（II）对应物[P * Ru（CO）]获得的异构体分布。观察到线性Hammett相关性log（k（X）/ k（H））= sigma（+）rho，rho =-0.57，表明源自铁（II）中心的亲电环丙烷化物种参与了反应中的反应中间体催化循环。当将反应混合物故意暴露于空气中时，在苯乙烯环丙烷化实验中观察到的对映选择性和反式/顺式比例的急剧下降进一步支持了这一点。还研究了轴向配体对选择性的影响。通过将有机碱如吡啶（py）和1-甲基咪唑（MeIm）添加到催化反应中，可以实现反式/顺式比例的大幅提高。通过电喷雾质谱法确定了轴向连接的铁卡宾部分[P * Fe（CHCO2Et）（py）]和[P * Fe（CHCO2Et）（MeIm）]的存在。对次级动力学同位素效应的研究表明，通过添加MeIm可以生成更多的产物状过渡态。

著录项

相似文献

  • 外文文献
  • 中文文献
  • 专利
获取原文

客服邮箱：kefu@zhangqiaokeyan.com

京公网安备：11010802029741号 ICP备案号：京ICP备15016152号-6 六维联合信息科技 (北京) 有限公司©版权所有

  • 客服微信

  • 服务号