Bicyclic phosphines as ligands for cobalt-catalysed hydroformylation

Abstract

A range of tertiary phosphine ligands derived from (R)-(+)-limonene was studied by HP-³¹P NMR, HP-IR, batch autoclave reactions and molecular modelling during the hydroformylation of 1-dodecene using a cobalt catalyst system and a metal ∶ ligand ratio of 1 ∶ 2. The phosphorus atom was incorporated in a limonene bicycle where the third substituent was systematically varied, Lim-R (R = (CH₂)₁₇CH₃, (CH₂)₉CH₃, (CH₂)₄CH₃, (CH₂)₃CH₃, (CH₂)₃C₆H₅, (CH₂)₃CN, (CH₂)₃OCH₂C₆H₅, (CH₂)₂OCH₂CH₃). The activity and selectivity was, to a large extent, governed by the equilibria between the modified and unmodified cobalt catalytic species in the reaction. Linearity ranged from 54 to 71% with Lim-(CH₂)₃CN yielding the most branched product and Lim-(CH₂)₄CH₃ the most linear product. The n ∶ iso ratio (ratio of linear to 2-methyl branched alcohol) also followed the same trend with a ratio of 2.6 for Lim-(CH₂)₃CN and 4.9 for Lim-(CH₂)₄CH₃. The rate decreased as the linearity increased with pseudo k values of 0.5 to 1.1. Hydrogenation of the alkene varied within a narrow band from 5–6%.