Ethylene, isolobal analogs

Another example involves the dimerization of the CH2 and butterfly d -ML4 fragments. The dimer of CH2 is just simply ethylene, a planar molecule characterized by a double bond between the two carbon atoms (a a bond and a tt bond). The isolobal analogy linking the CH2 and butterfly [Fe(CO)4] fragments (5-9) shows us that the... 

Use the isolobal analogy to predia the more stable conformations for the following ethylene complexes (Cp = ti -cyclopentadienyl). 

We will cover several more complexes that can be traced back to cyclopropane in the next section. For now, we note that the isolobal analogy nicely solves conformational issues. Let us rotate the ethylene unit in 21.19 and 21.20 by 90°. The ethylene tt orbital is now of Z>i symmetry and the / 2 orbital in CIU or ML is left occupied and nonbonding. Thus, 21.22 and 21.23 arc high-energy structures. 21.22... 

What is flie electronic structure of the Fe2(CO)g molecule This is not easy to say with no background. Could there be some multiple bonds between iron atoms of the a, n, or 8 character Well, flie isolobal analogy will allow us to say the following in fact. Fe2(CO)g is an ethylene-like molecule, with all consequences concerning the iron-iron bond (double), the planarity of (CO)2Fe=Fe(CO)2 fiagment, etc. Also, we will be able to predict that the Fe(CO)4 moiety resembles ( is isolobal with") the CH2, that it will hind to CH2, forming the H2C=Fe(CO)4, and can just replace CH2 in many other instances in organic chemistry. 

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