Preparation and properties of a but-2-enyl butadiene complex of cobalt and of an analogous complex from isoprene

Reaction of butadiene with cobalt(II) chloride in the presence of metallic zinc, ethanol, and triphenylphosphine gives the complex anti-π-but-2-enylbutadiene(triphenylphosphine)cobalt, (C4H7)(C4H6)CoPPh3. This is readily isomerized to the syn-isomer by action of PPh3, dimethyl sulphoxide, or pyridine. From isoprene an analogous complex (C5H9)(C5H8)CoPPh3 is obtained. The co-ordinated diolefin is displaced from these complexes by carbon monoxide to give the corresponding dicarbonyl derivatives. N.m.r. data for all of the complexes isolated are reported. Reaction of the complexes (C4H7)(C4H6)CoPPh3 and (C5H9)(C5H8)CoPPh3 with allene, 3-methyl-buta-1,2-diene, and acetylene gives highly crystalline linear polymers.