<p><b>二茂鎂</b>，有時簡稱 MgCp<sub>2</sub>，是一種有機鎂化合物，化學式 Mg(η<sup>5</sup>-C<sub>5</sub>H<sub>5</sub>)<sub>2</sub>。它是一種主族夾心配合物，結構類似過渡金屬的茂金屬，由中心鎂原子和兩個環戊二烯配體組成。
</p>


<h2><span id=".E5.88.B6.E5.A4.87"></span><span id="制备">製備</span></h2>
<p>二茂鎂是在1954年由恩斯特·奧托·菲舍爾和傑弗里·威爾金森獨立發現的。它可以由CpMgBr歧化或是金屬鎂和環戊二烯在500 °C 下反應而成。對於前者，茂基溴化鎂可以由乙基溴化鎂和環戊二烯反應而成，然後在220 °C 和10<sup>−4</sup> mbar下分解成MgCp<sub>2</sub> 和MgBr<sub>2</sub>：</p>
<dl><dd><span><span><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle \mathrm {Mg(C_{2}H_{5})Br\ {\xrightarrow[{-C_{2}H_{6}}]{+C_{5}H_{6},\ Et_{2}O}}\ Mg(C_{5}H_{5})Br{\xrightarrow[{-MgBr_{2}}]{x2,\ 220^{\circ }C,\ 10^{-4}mbar}}\ Mg(C_{5}H_{5})_{2}} }">
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          <mi mathvariant="normal">M</mi>
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    <annotation encoding="application/x-tex">{\displaystyle \mathrm {Mg(C_{2}H_{5})Br\ {\xrightarrow[{-C_{2}H_{6}}]{+C_{5}H_{6},\ Et_{2}O}}\ Mg(C_{5}H_{5})Br{\xrightarrow[{-MgBr_{2}}]{x2,\ 220^{\circ }C,\ 10^{-4}mbar}}\ Mg(C_{5}H_{5})_{2}} }</annotation>
  </semantics></math></span></span></dd>
<dd><small>Et<sub>2</sub>O = 乙醚</small></dd></dl><dl><dd><span><span><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle \mathrm {Mg\ +\ 2\ C_{5}H_{6}\ {\xrightarrow[{-H_{2}}]{500^{\circ }C}}\ Mg(C_{5}H_{5})_{2}\ } }">
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    <annotation encoding="application/x-tex">{\displaystyle \mathrm {Mg\ +\ 2\ C_{5}H_{6}\ {\xrightarrow[{-H_{2}}]{500^{\circ }C}}\ Mg(C_{5}H_{5})_{2}\ } }</annotation>
  </semantics></math></span></span></dd></dl><p>在實驗室里，可以由二烷基鎂和環戊二烯反應得到二茂鎂：</p>
<dl><dd><span><span><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle \mathrm {Mg(C_{4}H_{9})_{2}\ +\ 2\ C_{5}H_{6}\ \rightarrow \ Mg(C_{5}H_{5})_{2}\ +\ 2\ C_{4}H_{10}\uparrow \ } }">
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    <annotation encoding="application/x-tex">{\displaystyle \mathrm {Mg(C_{4}H_{9})_{2}\ +\ 2\ C_{5}H_{6}\ \rightarrow \ Mg(C_{5}H_{5})_{2}\ +\ 2\ C_{4}H_{10}\uparrow \ } }</annotation>
  </semantics></math></span></span></dd></dl><h2><span id=".E6.80.A7.E8.B4.A8"></span><span id="性质">性質</span></h2>
<p>室溫下，二茂鎂是一種白色固體。它的熔點為 176 °C，儘管在常壓下會在100 °C時升華。不像二茂鐵，二茂鎂會在極性、給電子溶劑中（例如醚和THF）會自耦電離：</p>
<dl><dd><span><span><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle {\ce {MgCp2 &lt;=&gt; MgCp+ + Cp-}}}">
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            <mtext>MgCp</mtext>
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              <mn>2</mn>
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    <annotation encoding="application/x-tex">{\displaystyle {\ce {MgCp2 &lt;=&gt; MgCp+ + Cp-}}}</annotation>
  </semantics></math></span></span></dd></dl><dl><dd><span><span><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle {\ce {MgCp2 + MgCp+ &lt;=&gt; Mg2Cp3+}}}">
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            <mtext>Mg</mtext>
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          <msubsup>
            <mtext>Cp</mtext>
            <mrow class="MJX-TeXAtom-ORD">
              <mn>3</mn>
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    <annotation encoding="application/x-tex">{\displaystyle {\ce {MgCp2 + MgCp+ &lt;=&gt; Mg2Cp3+}}}</annotation>
  </semantics></math></span></span></dd></dl><dl><dd><span><span><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle {\ce {MgCp2 + Cp- &lt;=&gt; MgCp3-}}}">
  <semantics>
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            <mtext>MgCp</mtext>
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              <mn>2</mn>
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            <mrow class="MJX-TeXAtom-ORD">
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          <mo>+</mo>
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            <mtext>MgCp</mtext>
            <mrow class="MJX-TeXAtom-ORD">
              <mn>3</mn>
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    <annotation encoding="application/x-tex">{\displaystyle {\ce {MgCp2 + Cp- &lt;=&gt; MgCp3-}}}</annotation>
  </semantics></math></span></span></dd></dl><p>二茂鐵在標準情況下穩定，但二茂鎂在氧氣或濕氣中迅速分解，所以在惰性氣氛下製備和儲存。</p>
<h2><span id=".E7.BB.93.E6.9E.84.E5.92.8C.E6.88.90.E9.94.AE"></span><span id="结构和成键">結構和成鍵</span></h2>
<p>通過X射線晶體學，固體二茂鎂的平均 Mg-C 和C-C鍵長分別為2.30 Å 和1.39 Å，兩個茂環是錯位的，點群D<sub>5d</sub>。氣相電子衍射顯示出相似的鍵長，不過兩個茂環是重疊的，點群 D<sub>5h</sub>。</p><p>關於Mg-Cp 的相互作用主要是離子鍵還是共價鍵一直存在激烈的爭論。
</p>
<h2><span id=".E5.8F.8D.E5.BA.94.E6.80.A7.E5.92.8C.E6.BD.9C.E5.9C.A8.E7.94.A8.E5.A4.84"></span><span id="反应性和潜在用处">反應性和潛在用處</span></h2>
<p>二茂鎂可以用來製備其它茂金屬：</p>
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  </semantics></math></span></span></dd></dl><p>在四氫呋喃里，二茂鎂會和 MgX<sub>2</sub>（X = 鹵素）交換配體，形成半夾心化合物CpMgX ：</p>
<dl><dd><span><span><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle {\ce {MgCp2 + MgX2 &lt;=&gt; 2 CpMgX}}}">
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  </semantics></math></span></span></dd></dl><p>反應產生的半夾心化合物可作為從有機鹵化物合成取代茂基的原料。</p><p>由於其高反應性，二茂鎂是半導體研究中的一個有吸引力的目標，可作為化學氣相沉積和摻雜應用的起始材料。</p><p>二茂鎂在下一代的鎂離子電池中，有作為電解質的潛在用途。</p>
<h2><span id=".E5.8F.82.E8.80.83.E8.B5.84.E6.96.99"></span><span id="参考资料">參考資料</span></h2>

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**二茂鎂**，有時簡稱 MgCp2，是一種有機鎂化合物，化學式 Mg (η5-C5H5)2。它是一種主族夾心配合物，結構類似過渡金屬的茂金屬，由中心鎂原子和兩個環戊二烯配體組成。

## 製備

二茂鎂是在 1954 年由恩斯特・奧托・菲舍爾和傑弗里・威爾金森獨立發現的。它可以由 CpMgBr 歧化或是金屬鎂和環戊二烯在 500 °C 下反應而成。對於前者，茂基溴化鎂可以由乙基溴化鎂和環戊二烯反應而成，然後在 220 °C 和 10−4mbar 下分解成 MgCp2 和 MgBr2：

　
: $\mathrm {Mg(C_{2}H_{5})Br\ {\xrightarrow[{-C_{2}H_{6}}]{+C_{5}H_{6},\ Et_{2}O}}\ Mg(C_{5}H_{5})Br{\xrightarrow[{-MgBr_{2}}]{x2,\ 220^{\circ }C,\ 10^{-4}mbar}}\ Mg(C_{5}H_{5})_{2}} $

　
: Et2O = 乙醚

　
: $\mathrm {Mg\ +\ 2\ C_{5}H_{6}\ {\xrightarrow[{-H_{2}}]{500^{\circ }C}}\ Mg(C_{5}H_{5})_{2}\ } $

在實驗室里，可以由二烷基鎂和環戊二烯反應得到二茂鎂：

　
: $\mathrm {Mg(C_{4}H_{9})_{2}\ +\ 2\ C_{5}H_{6}\ \rightarrow \ Mg(C_{5}H_{5})_{2}\ +\ 2\ C_{4}H_{10}\uparrow \ } $

## 性質

室溫下，二茂鎂是一種白色固體。它的熔點為 176 °C，儘管在常壓下會在 100 °C 時升華。不像二茂鐵，二茂鎂會在極性、給電子溶劑中（例如醚和 THF）會自耦電離：

　
: ${\ce {MgCp2 <=> MgCp+ + Cp-}}$

　
: ${\ce {MgCp2 + MgCp+ <=> Mg2Cp3+}}$

　
: ${\ce {MgCp2 + Cp- <=> MgCp3-}}$

二茂鐵在標準情況下穩定，但二茂鎂在氧氣或濕氣中迅速分解，所以在惰性氣氛下製備和儲存。

## 結構和成鍵

通過 X 射線晶體學，固體二茂鎂的平均 Mg-C 和 C-C 鍵長分別為 2.30 Å 和 1.39 Å，兩個茂環是錯位的，點群 D5d。氣相電子衍射顯示出相似的鍵長，不過兩個茂環是重疊的，點群 D5h。

關於 Mg-Cp 的相互作用主要是離子鍵還是共價鍵一直存在激烈的爭論。

## 反應性和潛在用處

二茂鎂可以用來製備其它茂金屬：

　
: ${\ce {MgCp2 + MCl2 -> MCp2 + MgCl2}}$

在四氫呋喃里，二茂鎂會和 MgX2（X = 鹵素）交換配體，形成半夾心化合物 CpMgX ：

　
: ${\ce {MgCp2 + MgX2 <=> 2 CpMgX}}$

反應產生的半夾心化合物可作為從有機鹵化物合成取代茂基的原料。

由於其高反應性，二茂鎂是半導體研究中的一個有吸引力的目標，可作為化學氣相沉積和摻雜應用的起始材料。

二茂鎂在下一代的鎂離子電池中，有作為電解質的潛在用途。

## 參考資料
1284-72-6