Mechanistic insights into the phosphine ligand-dependent regioselectivity of Rh-catalyzed 1-octene hydroformylation

Abstract

Hydroformylation of long-chain α-olefins to linear aldehydes is of industrial importance for the sustainable production of value-added linear aldehydes. However, achieving regioselectivity remains challenging due to the steric and electronic effects imposed by the ligand environment, underscoring the need for a molecular-level mechanistic understanding to guide rational catalyst design. In this work, we present a comprehensive density functional theory (DFT) investigation into the mechanistic origins of ligand-controlled regioselectivity in Rh-catalyzed 1-octene hydroformylation. By systematically examining three representative ligand systems including monodentate phosphine (PPh₃), monodentate phosphite (TPO), and bidentate phosphite (BIP), we identify the olefin insertion as the regioselectivity-determining step. The calculations reveal that the superior performance of the BIP catalyst arises from a synergistic interplay between steric and electronic effects, in which its characteristic equatorial–axial coordination mode constructs a rigid and asymmetric steric confinement that preferentially stabilizes the linear insertion pathway. Quantitative free-energy analysis predicts pronounced differences in regioselectivity, corresponding to theoretical linear-to-branched (L/B) ratio of 19.93 for BIP, substantially exceeding those of the benchmark PPh₃ system (9.24) and the sterically less hindered TPO system (2.75). These predictions are corroborated by experimental results that reproduce the same regioselectivity trend (BIP > PPh₃ > TPO), thereby validating a steric–electronic cooperative control model and providing a rational framework for designing high-performance catalysts for selective functionalization of long-chain olefins.