Optimization of Xantphos-type ligands for highly linear-selective hydroformylation of allyl alcohol and alkenes.

Xantphos-type ligands enabled the highly linear-selective hydroformylation of allyl alcohol and related alkenes under mild conditions with RhH(CO)(PPh3)3. The product, 4-hydroxybutanal, is widely used as an industrial solvent and polymer precursor, and serves as an industrial intermediate in the production of 1,4-butanediol, γ-butyrolactone, and N-methyl-2-pyrrolidone. Six ligands with different combinations of the Xantphos backbone and substituents on the benzene ring were compared. A 3,5-xylyl-substituted ligand displayed particularly high regioselectivity toward linear products. Density functional theory calculations clarified that this preference arises from a lower activation barrier for 1,2-insertion compared to 2,1-insertion.