Ferrocene

Japanese: フェロセン

[Fe( η ⁵ -C ₅ H ₅ ) ₂ ] (186.04). Bis( η ⁵ -cyclopentadienyl)iron(II). It was the first sandwich complex synthesized, a stable compound in which cyclopentadienyl (C ₅ H ₅ ) ^- are coordinated in a sandwich shape above and below the iron atom. In 1951, JJ Kealy and PL Pauson obtained stable orange-red crystals in an attempt to synthesize fulvalene, but this compound did not exhibit the properties of cyclopentadiene and was aromatic, so it was named ferrocene. Between 1952 and 1953, X-ray diffraction and infrared absorption spectroscopy confirmed that this compound had a sandwich structure. It can be synthesized by reacting anhydrous ferric chloride, FeCl ₃ , with cyclopentadienylmagnesium bromide, by reacting FeCl ₂ with cyclopentadienylsodium or cyclopentadienyllithium, or by reacting FeCl ₂ with cyclopentadiene in the presence of a base such as diethylamine. Its melting point is 173-174 °C, its boiling point is 249 °C. Its density is 1.49 g cm ^-3 . It is soluble in common organic solvents, but insoluble in water. It sublimes above 100 °C. It is diamagnetic, and when oxidized in air in the presence of an acid, it produces the blue bis( η ⁵ -cyclopentadienyl)iron(III) ion [Fe(C ₅ H ₅ ) ₂ ] ⁺ . Like other aromatic compounds, it is prone to electrophilic reactions. The arrangement of the two five-membered rings is said to be staggered (Figure (a)), but in the crystal at -175 °C it is staggered (Figure (b)), and up to -109 °C it is close to staggered, but the upper and lower five-membered rings are rotated by about 9°. There is no evidence that it forms a staggered structure at room temperature. In the gas state it forms an staggered structure. Theoretically, the staggered structure is 2.78 kJ mol ^-1 more stable than the staggered structure. On the other hand, most metallocenes are staggered, and the pentamethyl-substituted derivative [Fe{C ₅ (CH ₃ ) ₅ } ₂ ] is staggered. Those that have other metal ions in place of Fe ²⁺ are collectively called metallocenes. [CAS 102-54-5]

Source: Morikita Publishing "Chemical Dictionary (2nd Edition)" Information about the Chemical Dictionary 2nd Edition

Japanese:

[Fe(η⁵-C₅H₅)₂](186.04)．ビス(η⁵-シクロペンタジエニル)鉄(Ⅱ)のこと．最初に合成されたサンドイッチ錯体で，鉄原子の上下にシクロペンタジエニル (C₅H₅)^－がサンドイッチ状に配位した安定な化合物．1951年に，J.J. KealyとP.L. Pausonはフルバレンを合成しようとして安定な橙赤色の結晶を得たが，この化合物はシクロペンタジエンの性質を示さず，しかも芳香族性を示すので，フェロセンと名づけられた．1952年から1953年にかけて，X線回折，赤外吸収スペクトルにより，この化合物がサンドイッチ構造であることが確かめられた．合成法には，無水塩化鉄FeCl₃と臭化シクロペンタジエニルマグネシウムとの反応，FeCl₂とシクロペンタジエニルナトリウムまたはシクロペンタジエニルリチウムとを反応させる方法，ジエチルアミンのような塩基の存在下にFeCl₂とシクロペンタジエンとを反応させる方法などがある．融点173～174 ℃，沸点249 ℃．密度1.49 g cm^－3．普通の有機溶媒に可溶，水に不溶．100 ℃ 以上で昇華する．反磁性で，酸の共存下で空気酸化すると，青色のビス(η⁵-シクロペンタジエニル)鉄(Ⅲ)イオン [Fe(C₅H₅)₂]^＋を生じる．ほかの芳香族化合物と同じく，求電子反応が起こりやすい．二つの五員環の配置はねじれ形(図(a))とされたが，結晶中－175 ℃ では，重なり形(図(b))であり，－109 ℃ までは重なり形に近いが，上下の五員環が約9°回転した配置をとっている．室温で，ねじれ形構造をとる証拠は得られていない．ガス状態では重なり形をとる．理論的には重なり形が2.78 kJ mol^－1 だけねじれ形より安定である．一方，多くのメタロセンはおもにねじれ形であり，またペンタメチル置換体の[Fe{C₅(CH₃)₅}₂]はねじれ形である．Fe²⁺ のかわりにほかの金属イオンの入ったものを総称してメタロセンという．[CAS 102-54-5]