Unraveling the Origin of the Regioselectivity of a Supramolecular Hydroformylation Catalyst

Supramolecular substrate preorganization using DIMPHos ligands, which are bisphosphine ligands equipped with a carboxylate binding site, allows for control over the regioselectivity in the hydroformylation reaction. In all reported examples, the aldehyde product in which the CO was inserted farthest from the directing group, was formed in excess (for terminal alkenes the linear aldehyde). We report here an in-depth DFT study to provide mechanistic insight into this selective transformation. These calculations show large energy differences between the different hydride migration steps of competing pathways that lead to either the linear or branched aldehyde product, in line with the experimentally found selectivity. Through the use of calculated model systems of the catalyst, it is shown that the substrate binding event itself plays an important role in determining these large energy differences. Following ditopic substrate binding, the product forming pathways that lead to the minor isomeric product is particularly disfavored by the steric repulsion between the ditopically bound substrate and the apical coordinated CO ligand.