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首页> 外文期刊>Organometallics >Mechanistic Studies on a Facile Ring-Flipping Process in Planar Chiral Ferrocenes under Ambient and High Pressure and Its Relevance to Asymmetric Catalysis
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Mechanistic Studies on a Facile Ring-Flipping Process in Planar Chiral Ferrocenes under Ambient and High Pressure and Its Relevance to Asymmetric Catalysis

机译：平面高压下手性二茂铁中环容易翻转的机理及其与不对称催化反应的关系

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摘要

The bis-planar chiral ferrocenyldiphosphine bis(l-(diphenylphosphino)-eta~5-indenyl)iron(II) is observed to undergo an isomerization from the meso isomer to the rac isomer in THF solvent at ambient temperature. This process requires ring flipping of one of the indenyl ligands. The isomerization is slowed by the addition of the noncoordinating solvent chloroform and is accelerated by addition of salts such as LiCl and LiClO_4. Rate and activation parameters have been determined for the spontaneous isomerization: kappa_(obs) - 1.6 x 10~(-5) s~(-1) at 23degC,DELTAH = 58 ± 4 kJ mol~(-1), DELTAS= -140 ± 15 J mol~(-1) K~(-1) and DELTAV = -12.9 ± 0.8 cm~3 mol~(-1). Labeling of the ferrocene with deuterium in the 3- and 3'-positions followed by isomerization showed no incorporation of deuterium into the 2- or 2'-positions, thus ruling out 1,2-hydrogen-shift mechanisms. Attempted crossover experiments with dideuterated and nondeuterated ferrocenes gave no monodeuterated products of crossover, thus ruling out ligand dissociative mechanisms. The proposed isomerization mechanism involves coordination of two THF ligands with ring slippage of one indenide and then displacement of that indenide and coordination through the phosphine. Coordination of the indenide by the other face in the reverse process then leads to the other isomer.
机译：观察到在室温下，双平面手性二茂铁基二膦双（1-（二苯基膦基）-η5-5-茚基）铁（II）经历了从内消旋异构体到外消旋异构体的异构化。该过程需要茚基配体之一的环翻转。通过添加非配位溶剂氯仿来减慢异构化，并且通过添加诸如LiCl和LiClO 4的盐来加速异构化。已经确定了自发异构化的速率和活化参数：在23°C下kappa_（obs）-1.6 x 10〜（-5）s〜（-1），DELTAH = 58±4 kJ mol〜（-1），DELTAS =- 140±15 J mol〜（-1）K〜（-1），DELTAV = -12.9±0.8 cm〜3 mol〜（-1）。用3-和3'-位的氘标记二茂铁，然后进行异构化，表明没有将氘掺入2-或2'-位，因此排除了1,2-氢转移机理。尝试使用双氘代和非氘代二茂铁进行交叉实验时，未得到交叉的单氘代产物，因此排除了配体解离机理。拟议的异构化机理涉及两个THF配体的配位与一个茚化物的环滑移，然后取代该茚化物并通过膦进行配位。然后，在相反的过程中，茚化物与另一面的配位导致另一异构体。

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