N-Pyrrolylphosphines as ligands for highly regioselective rhodium-catalyzed 1-butene hydroformylation: effect of water on the reaction selectivity

Abstract

The hydroformylation of 1-butene catalyzed by Rh(acac)(CO)₂ with an excess of N-pyrrolylphosphine ligands, L = P(NC₄H₄)₃, PPh₂(NC₄H₄) or PPh(NC₄H₄)₂, was investigated under constant pressure of synthesis gas (4–10 bar, H₂/CO = 1) and 2 bar of 1-butene at temperatures ranging from 50 to 80 °C. N-Pyrrolylphosphine ligands facilitated excellent selectivity towards aldehydes and regioselectivity towards linear aldehydes. The application of a higher temperature, the presence of a small amount of water, and a [L]/[Rh] ratio of ca. 13 resulted in the achievement of the highest n/iso values in a short time. A further increase in selectivity was achieved after the addition of water to the reaction mixture. The catalytic performance of the studied systems showed an increase in selectivity (n/iso) with the increase of the number of pyrrolyl groups in phosphine: (P(NC₄H₄)₃ > PPh(NC₄H₄)₂ > PPh₂(NC₄H₄)) > PPh₃.