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%.