Valorisation of mixtures of linear alkenes using cobalt-mediated isomerisation and hydroformylation chemistries

Abstract

Active catalysts derived from cobalt and the Xantphos ligand were synthesised, characterised and tested in the hydroformylation of pure linear alkenes or their mixtures. The preformed complex [Co₂(CO)₆(Xantphos)] showed similar reactivity and selectivity towards aldehydes to the active catalyst formed in situ from equimolar amounts of [Co₂(CO)₈] and Xantphos. In the case of oct-1-ene, the linear aldehyde was obtained with good chemo- and regio-selectivity (linear to branched ratio was up to 75 : 25). For all octene isomers, tandem isomerisation–hydroformylation processes took place. Regioselectivities for all the studied octene isomers remained practically constant, independent of the position or geometry of the CC double bond in the starting material. Moreover, by-products were formed in similarly small amounts for all the octene isomers. We also demonstrated that this chemistry is an interesting strategy for valorising mixtures of linear hexenes, heptenes or octenes by transforming the initial mixture into one major aldehyde (addition of a CHO group to the C₁ carbon of the alkene skeleton, up to 73% selectivity). Moreover, these mixtures of alkenes were hydroformylated with low final amounts of non-hydroformylated alkenes, hydrogenated alkenes and alcohols.