How can I draw metallocenes in ChemDraw?

How can I properly draw the structure of metallocenes (e.g. ferrocene) and similar sandwich compounds in ChemDraw?


![ferrocene](https://i.stack.imgur.com/UIuIL.png)


In particular, two problems cannot be solved with the usual workflow when building a molecule in ChemDraw:


* How can I draw a bond starting from the centre of a ring structure (e.g. cylopentadienyl or benzene) if there is no atom?
* How can I connect the centre of another ring structure to an existing molecule with the correct bond length and angle?




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This question came up among the editorial staff of the chemistry section of the German Wikipedia. I have answered this question there myself, and I think it might be useful to [share](https://stackoverflow.blog/2011/07/its-ok-to-ask-and-answer-your-own-questions/) the solution to this problem here.




In the first step, separately draw the individual ring structures. ChemDraw comes with an template library of predrawn structures, including some suitable cyclopentadienyl rings.


[![enter image description here](https://i.stack.imgur.com/ZR5nR.png)](https://i.stack.imgur.com/ZR5nR.png)


You can place the ring structures anywhere in your document.


[![enter image description here](https://i.stack.imgur.com/1loEz.png)](https://i.stack.imgur.com/1loEz.png)


Select one ring structure. On the *Structure* menu, click *Add Multi-Center Attachment*. This adds a multi-center node as attachment point to the structure.


[![enter image description here](https://i.stack.imgur.com/dZ33X.png)](https://i.stack.imgur.com/dZ33X.png)


Repeat this process for the other ring structure. Asterisks indicate the created multi-center nodes.


[![enter image description here](https://i.stack.imgur.com/ttskj.png)](https://i.stack.imgur.com/ttskj.png)


You can use the multi-center attachment points to draw the coordination bonds. Note that bonds connecting to delocalized systems should be drawn as plain bonds; it is not acceptable to use dashed bonds. When one bond crosses another, if necessary, you can click *Bring to Front* or *Send to Back* on the *Object* menu to indicate which bond is in front. The bond which is behind will have a small section cut out.


[![enter image description here](https://i.stack.imgur.com/BrWUG.png)](https://i.stack.imgur.com/BrWUG.png)


Click to select the end (i.e. the terminal atom) of the coordination bond in one structure, and then shift+click to select the end of the coordination bond in the second structure. On the *Object* menu, click *Join*.


[![enter image description here](https://i.stack.imgur.com/lx3dG.png)](https://i.stack.imgur.com/lx3dG.png)


The two structures are joined so that they share an atom. Note that the second structure is moved accordingly.


[![enter image description here](https://i.stack.imgur.com/m8pA6.png)](https://i.stack.imgur.com/m8pA6.png)


Finally, you can add any substituents as required. 


(Also note that for unsubstituted ferrocene in the gas phase, the cyclopentadienyl rings are actually eclipsed.)


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