• 主题
高级搜索  >
历史搜索 清空历史
首页> 外文期刊>Chemistry: A European journal >Silver phosphanes partnered with carborane monoanions: synthesis, structures and use as highly active lewis acid catalysts in a hetero-diels-alder reaction
【24h】

Silver phosphanes partnered with carborane monoanions: synthesis, structures and use as highly active lewis acid catalysts in a hetero-diels-alder reaction

机译：磷化氢银与碳硼烷单阴离子结合：合成，结构和在杂狄尔斯-阿尔德反应中用作高活性路易斯酸催化剂

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

Four Lewis acidic silver phosphane complexes partnered with [1-closo-CB_(11)H_(12)]~- and [1-closo-CB_(11)H_6Br_6]~- have been synthesised and studied by solution NMR and solid-state X-ray diffraction techniques. In the complex [Ag(PPh_3)(CB_(11)H_(12)] (1), the silver is coordinated with the carborane by two stronger 3c-2e B-H-Ag bonds, one weaker B-H-Ag interaction and a very weak Ag…C_(arene) contact in the solid state. In solution, the carborane remains closely connected with the {Ag(PPh_3)}~+ fragment, as evidence by ~(11)B chemical shifts. Complex 2 [Ag(PPh_3)_2(CB_(11)H_(12)]_2 adopts a dimeric motif in the solid state, each carborane bridging two Ag centres. In solution at low temperature, two distinct complexes are observed that are suggested to be monomeric [Ag(PPh_3)_2][(CB_(11)H_(12)]_2 and dimeric [Ag(PPh_3)_2(CB_(11)H_(12)]_2. With the more wealky coordinating anion [CB_(11)H_6Br_6]~- and one phosphane, complex 3 [Ag(PPh_3)_2(CB_(11)H_6Br_6] is isolated. Complex4, [Ag(PPh_3)_2(CB_(11)H_6Br_6], has been characterised spectroscopically. All of the complexes have been assessed as Lewis acids in the hetero-Diels-Alder reaction of N-benzylideneaniline with Danishefsky's diene. Exceptionally low catalyst loadings for this Lewis acid catalysed reaction are required (0.1 mol%) coupled with turnover frequencies of 4000 h~(-1) (quantitative conversion to product after 15 minutes using 3 at room temperature). Moreover, the reaction does not occur in rigorously dry solvent as addition of a substoichiometric amount of water (50 mol%) is necessary for turnover of the catalyst. It is suggested that a Lewis assisted Bronsted acid is formed between the water and the silver. The effect of changing the counterion to [BF_4]~-, [OTf]~- and [ClO_4]~- has also been studied. Significant decreases in reaction rate and final product yield are observed on changing the anion from [CB_(11)H_6Br_6]~-, thus demonstrating the utility of weakly coordinating charborane anions in organic synthesis.
机译：通过溶液NMR和固相研究合成了四种与[1-closo-CB_（11）H_（12）]〜-和[1-closo-CB_（11）H_6Br_6]〜-结合的路易斯酸性银膦配合物X射线衍射技术。在复合物[Ag（PPh_3）（CB_（11）H_（12）]（1）中，银通过两个更强的3c-2e BH-Ag键，一个较弱的BH-Ag相互作用和一个非常弱的键与碳硼烷配位Ag…C_（芳烃）以固态接触，在溶液中，碳硼烷保持与{Ag（PPh_3）}〜+片段紧密相连，这是〜（11）B化学位移的证明络合物2 [Ag（PPh_3） _2（CB_（11）H_（12）] _ 2处于固态的二聚体基元，每个碳硼烷都桥接两个Ag中心。在低温溶液中，观察到两个明显的复合物，建议它们是单体[Ag（PPh_3） _2] [（CB_（11）H_（12）] _ 2和二聚体[Ag（PPh_3）_2（CB_（11）H_（12）] _ 2。具有更弱的配位阴离子[CB_（11）H_6Br_6]〜-和分离出一种膦，配合物3 [Ag（PPh_3）_2（CB_（11）H_6Br_6]。已通过光谱法表征了配合物4 [Ag（PPh_3）_2（CB_（11）H_6Br_6]。路易斯酸在N-亚苄基苯胺与Danishefsky's二烯的杂Diels-Alder反应中。此路易斯酸催化的反应需要极低的催化剂负载量（0.1 mol％），以及周转频率为4000 h〜（-1）（15分钟后在室温下使用3定量转化为产物）。此外，在严格干燥的溶剂中不会发生反应，因为对于催化剂的周转需要添加亚化学计量的水（50mol％）。建议在水和银之间形成路易斯辅助的布朗斯台德酸。还研究了将抗衡离子改变为[BF_4]〜-，[OTf]〜-和[ClO_4]〜-的效果。从[CB_（11）H_6Br_6]〜-改变阴离子，观察到反应速率和最终产物收率的显着降低，从而证明了弱配位的甲硼烷阴离子在有机合成中的效用。

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