THERMOCHEMISTRY AND STRUCTURES OF COC3H6+ - METALLACYCLE AND METAL-ALKENE ISOMERS

The thermochemistry for the metallacyclic and metal-alkene isomers of CoC3H6+ is studied in a guided-ion-beam mass spectrometer. A flow-tube source is used to produce thermalized CoC3H6+ ions formed by condensation of Co+ with propene and cyclopropane, and by the decarbonylation of cyclobutanone by Co+ These ions are then studied by threshold collisional activation and the results compared with the bimolecular reactivity of Co+ with cyclopropane and propene. The results are interpreted to indicate that CoC3H6+ ions formed in these three methods have both the Co+-propene and cobaltacyclobutane ion structures in ratios of 100:0, 85:15, and 40:60, respectively. Some evidence for a third isomer, tentatively identified as the cobalt pi-allyl hydride ion complex, is also obtained. Reactivity and thermochemical differences of the ions produced in these three different ways are discussed and compared to previous work by other investigators and to work on these isomers of FeC3H6+. Analysis of the kinetic energy dependence of the cross sections allows the determination of the 0 K bond dissociation energies: 1.87 +/- 0.07 eV for Co+-propene and 0.93 +/- 0.07 eV for cobaltacyclobutane to dissociate and yield Co+ + propene. We also determine 0 K bond dissociation energies for Co+-C3H5, Co+-C3H4 and Co+-C2H3 to be 2.01 +/- 0.17, 0.81 +/- 0.09, and 2.10 +/- 0.08 eV, respectively, and revise our reported 0 K bond energy for Co+-CH2 to 3.24 +/- 0.06 eV.