Rhodium-catalysed hydroformylation of branched 1-alkenes; Bulky phosphite vs triphenylphosphine as modifying ligand

The influence of alkyl substituents in l-alkene substrates in the rhodium-catalysed hydroformylation in the presence of tris(2-tert-butyl-4-methylphenyl) phosphite has been studied and compared with that observed for the reaction involving the conventional PPh(3)-modified catalyst. Hindered alkenes underwent hydroformylation at good rates (i.e. 1300 mol (mel Rh)(-1) h(-1) for 3,3-dimethyl-1-butene as T = 70 degrees C and P = 20 bar (H-2-CO)); under mild conditions the rates were only slightly affected by the alkyl substituents. The selectivity towards the linear aldehyde increases progressively with substitution, from 66% for 1-octene up to 100% for 3,3-dimethyl-1-butene, and the proportion of isomerized alkenes remained substantial (up to 17.4% for allylcyclohexane). The differences between the two systems are explained in terms of the different kinetics observed for them.