COBALT METALLOCYCLES .6. PREPARATION AND STRUCTURE OF COBALTACYCLOPENTENE COMPLEXES AND THEIR REACTIONS WITH OLEFINS AND ACETYLENES

(η2-Acetylene)(η5-cyclopentadienyl)(triphenylphosphine)cobalt, Co(C5H5)(R1CɡCR1)(PPh3) (1), where R1 = Ph or CO2Me, R2 = CO2Me, reacts with 1, 2-disubstituted olefins (dimethyl maleate, dimethyl fumarate, fumaronitrile, crotononitrile) to form novel metallocyclopentene complexes, (η5-C5)(PPh3)[formula omitted](2). A kinetic study indicates an intermediate in which acetylene and olefin are simultaneously coordinated to cobalt. One of the cobaltacyclopentene complexes, 2a (R1 = Ph; R2 = R3 = R4 = CO2Me), has been characterized by an X-ray crystal-structure analysis. In contrast, monosubstituted olefins (acrylonitrile, methyl acrylate) react with 1 to give cobalt-diene complexes of the composition Co(C5H5)[(acetylene)(olefin)2] (4). That these compounds (4) are presumably formed via cobaltacyclopentene intermediates is evidenced by the fact that a similar diene complex is formed when 2a is reacted with acrylonitrile Diphenylacetylene and acrylonitrile cotrimerize in the presence of a catalytic amount of Co(C5H5)(PhC2Ph)(PPh3) (1c) to give a linear diene of the composition (PhC2Ph)(CH2CHCN)2. The reaction of 2a with acetylenes yields cobalt-cyclohexadiene complexes. © 1979, American Chemical Society. All rights reserved.