Tricarbonyl iron tetracyanoethylene, reaction with

The reaction of o-diphenylcyclobutadiene (generated in situ by oxidation of its iron tricarbonyl complex) with p-benzoquinone yields A as the exclusive product. With tetracyanoethylene, however, B and C are formed in a 1 7 ratio. Discuss these results, and explain how they relate to the question of the square versus rectangular shape of cyclobutadiene. 

Reaction of tricarbonyl(tropone)iron with tetracyanoethylene gave the 1 1 adduct (602) the similar reaction of the 2-deuteriotropone complex gave exclusively (603). It is concluded that electrophilic attack by TCNE occurs exo to the iron atom and at a non-co-ordinated double bond of the substrate. The tricarbonyl(bicyclo[6,l,0]nona-2,4,6-triene)chromium complex is reported to rearrange at 100 °C almost completely to (604). 2... 

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