Olefin Insertion into the Rhodium-Hydrogen Bond as the Step Determining the Regioselectivity of Rhodium-Catalyzed Hydroformylation of Vinyl Substrates: Comparison between Theoretical and Experimental Results

A comparison between experimental and theoretical data on regioselectivity concerning the hydroformylation of several vinyl substrates (propene, 2-methylpropene, 1-hexene, 3,3-dimethylbutene, fluoroethene, 3,3,3-trifluoropropene, vinylmethylether, allylmethylether, styrene) with unmodified rhodium catalysts is reported. Various H-Rh(CO)3-olefin complexes are examined at the B3P86/3-21G or /6-31G* level (ECP & LANL2DZ for Rh) and compared to the adducts with modified catalysts, such as H-RhPH3(CO)2. The computed geometries are in satisfactory agreement with the X-ray ones. The activation energies for the alkyl rhodium intermediate formation, computed at either level along the pathways to branched or linear aldehydes, allow one to predict the regioselectivity ratios, since they are in very good agreement with the experimental ones evaluated for the isomeric aldehydes.