Cyclobutadiene complexes, -coordinated ring

The X-ray study 170, 171) established a planar structure for the cyclobutadiene ring with C-—C distance equal to 1.46 A and angles of 90°. All the M—C distances are equivalent and close to those observed in ferrocene. The phenyl and methyl substituents are distorted from the ring plane and bent towards the metal atom. If one assumes that cyclobutadiene occupies two coordination sites then in the known tetraphenylcyclobutadiene-nickel and -palladium complexes the metal atom has a coordination number of 5. This suggests coordinative unsaturation for the metal and a priori one may expect an associative substitution for such complexes. 

POLYMERS CONTAINING METALLACYCLOPENTADIENE RINGS AND CYCLOBUTADIENE RINGS COORDINATED TO CYCLOPENTADIENYL METAL COMPLEXES... 

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