30268-70-3Relevant articles and documents
Carbon-carbon bond-forming reactions of cobaltacyclopentene/cobaltaoxanorbornadiene complexes with isocyanides, carbon monoxide, and alkynes
Scozzafava, Maryrose,Stolzenberg, Alan M.
, p. 1073 - 1083 (2008/10/08)
Reaction of (η5-C5H5)Co[C(R)C(CO2CH 3)CH(CO2CH3)CH(CO2CH 3)][P(C6H5)3] (R = C6H5, 2a; R = CO2CH3, 2b) with isocyanides, CO, and diphenylacetylene (DPA) afforded 1-amino-1,3-cyclopentadienes, cyclopent-2-enones, and (η5-C5H5)Co(η 4-1,3-cyclohexadiene) complexes, respectively. The related [2.2.1]-metallabicyclic cobaltaoxanorbornadiene complexes 1a and 1b reacted with the same reagents to afford identical products. Reactions with isocyanides and CO proceeded in two distinct steps: (1) co-ordination of the reactant to cobalt to form a new ligand-substituted cobaltacyclopentene complex and (2) insertion of the reactant into the metallacycle, followed by reductive elimination. Intermediates were not detected in the reactions with DPA. However, the isolation of isomeric η4-cis-5,6-dicarbomethoxy-1,3-cyclohexadiene complexes with CpCo coordinated on different faces of the diene suggested the intermediacy of a metallacycloheptadiene complex. Kinetic measurements established that the reaction of 1a with DPA was first order with respect to both reagents. A rate constant for the reaction of 2a with DPA was calculated from our data and the known equilibrium constant between 2a, 1a, and P(C6H5)3. The agreement of the calculated rate with a published rate for the reaction confirmed that 1a is the kinetically significant intermediate in the carbon-carbon bond-forming reactions of 2a.