The activation of CH bonds in internal alkenes and dienes by {NiCp} species formed in the reaction of nickelocene with alkali metals
摘要:
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)(3)RC=CR and with di(cyclopentadienylnickel) (NiCp)(2)RC=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(cyclopentadienyinickel) clusters. In the reaction of nickelocene with lithium in the presence of 1,5-hexadiene, alkylidyne tri(cyclopentadienylnickel) cluster (NiCP)(3)CCH2CH2CH2CH=CH2 and intramolecularly stabilised complex Cp NiCH(CH3)CH2CH2CH = CH2 were formed. In all the reactions studied di-, (NiCP)(2)CpH, and tetra(cyclopentadienylnickel), (NiCP)(4)H-x, compounds were formed besides the other products. (C) 2002 Elsevier Science B.V. All rights reserved.