Rhodium-catalyzed hydroformylation of isoprene has been studied in the presence of various mono-
and diphosphines. Using a large excess of the ligand, the reaction can be performed under mild conditions
(80−100 °C, 40−80 atm) and results in three unsaturated aldehydes formed in a 95% combined selectivity.
The study of the effects of the reaction variables revealed remarkable trends, opposite those usually
observed with simple alkenes. The increase in the concentration of the phosphorus ligand and/or ligand
basicity strongly accelerates the reaction. Moreover, the reaction shows unusual kinetics, being first order
in both hydrogen and CO pressure under “common” hydroformylation conditions. The obtained data
confirm that an η3−η1 rearrangement, which converts an η3-allylrhodium intermediate resistant to CO
insertion into the much more reactive η1 complex, is the most critical step of this reaction.
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