The first metal complexes of bicyclopropylidene, a unique tetrasubstituted alkene ligand

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The reactions of bicyclopropylidene 2 with bis(cyclopentadienyl)bis(trimethylphosphane)titanium( II) 1 and with the cobalt chelate 4 give the first known metal complexes of bicyclopropylidene 3 and 7, respectively, in good yields; the bicyclopropylidene cobalt complex 7 is characterized by an X-ray crystal structure analysis which shows a severe out-of-plane bending of the alkenic ligand, indicating considerable back-bonding which goes along with a release of strain in the ligand.