The activation of CH bonds in internal alkenes and dienes by {NiCp} species formed in the reaction of nickelocene with alkali metals

Reactions of nickelocene with metallic sodium in the presence of internal alkenes: trans-3-hexene, cis-2-heptene and 2,3-dimethyl-2-butene have been studied. It was found that {NiCp} species generated in the reaction of nickelocene with sodium dehydrogenate internal alkenes to alkynes. The latter form then complexes with tri(cyclopentadienylnickel) (NiCp)3RCCR and with di(cyclopentadienylnickel) (NiCp)2RCCR. If the methyl group is adjacent to the alkene double bond, the activation of the CH bonds of this group leads to the formation of alkylidyne tri(cyclopentadienylnickel) clusters. In the reaction of nickelocene with lithium in the presence of 1,5-hexadiene, alkylidyne tri(cyclopentadienylnickel) cluster (NiCp)3CCH2CH2CH2CHCH2 and intramolecularly stabilised complex CpCH2 were formed. In all the reactions studied di-, (NiCp)2CpH, and tetra(cyclopentadienylnickel), (NiCp)4Hx, compounds were formed besides the other products.