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

Abstract

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.