Nickel catalyzed dimerization reactions of vinylidene compounds: Head-to-head couplings and catalyst stabilization

•Nickel catalyzed head-to-head co-dimerization of isobutene with 1-alkenes.•Substrates influences on catalytic activity and product selectivity.•Catalyst stabilization by additives with internal electron poor double bonds.

Co-dimers of the vinylidene compound isobutene with different 1-alkenes as well as homo-dimers from other vinylidene compounds are generated in high selectivities using (4-cyclooctene-1-yl)(1,1,1,5,5,5-hexafluoro-2,4-acetylacetonato)nickel as a catalyst. Regarding co-dimerization reactions very high selectivies for head-to-head couplings of up to 99% are achieved. Beside co-dimers as main products, homo-dimers of both substrates are obtained as relevant by-products. By careful variation of the initial proportion of substrates the distribution of co-dimers and homo-dimers can effectively be adjusted. Depending on shifts in product selectivity a deeper insight into the insertion mechanism is concluded. Although head-to-head couplings of other vinylidene compounds are also feasible with very high selectivities of >99%, different limitations for the catalytic system are shown. Subsequent considerations result in an extension of catalyst lifetime applying additives with internal electron-poor double bonds.

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