Reactions of CoCp(1+) (Cp = cyclopentadienyl) with Hydrocarbons in the Gas Phase. Observation of Novel Skeletal Isomerizations/Dehydrocyclizations Resulting in Cobaltocenium Formation

Article abstract of DOI:10.1021/ja00311a030

The gas-phase reactions of CoCp(1+) with a variety of hydrocarbons are described by using Fourier transform mass spectrometry (FTMS).All aliphatic alkanes larger than methane (except 2,2-dimethylpropane) are dehydrogenated by CoCp(1+) with no C-C bond cleavages observed.Collisional activation of CoCp(olefin)(1+) species derived from C5 and C6 alkanes, as well as reactions of CoCp(1+) with isomeric pentenes and hexenes, are dominated by skeletal isomerization followed by dehydrocyclization forming cobaltocenium.Dehydrocyclization of linear C5 olefins is more facile than skeletal isomerization of branched C5 olefins.Reactions with cyclopropane and cyclobutane proceed by initial insertion across the strain-weakened C-C bonds.For cyclopropane, insertion into a C-C bond results in initial formation of a cobaltcyclobutane species which undergoes dehydrogenation exclusively.With cyclobutane, both dehydrogenation and symmetric ring cleavage occur for the cobaltacyclopentane species.CoCp(1+) reacts with cyclopentane and cyclohexane by attacking C-H bonds exclusively.Finally, D^o(CoCp(1+)-Cp) = 118 +/- 10 kcal/mol and D^o(Co(1+)-Cp) = 85 +/- 10 kcal/mol are assigned from the observed reactivities.