PI-STACKING AND THE PLATINUM-CATALYZED ASYMMETRIC HYDROFORMYLATION REACTION - A MOLECULAR MODELING STUDY

The importance of steric factors in determining the regioselectivity of a class of platinum(II) hydroformylation catalysts (L2Pt(CO)X) has been theoretically examined by using an augmented Dreiding force field. This paper characterizes the differential stabilization of the initially formed platinum alkyl complexes resulting from styrene insertion into a Pt-H bond to form either the primary phenethyl product (leading to normal or linear aldehyde) or the secondary alpha-methyl styryl intermediate (leading to branched aldehyde). The alpha-methyl styryl products displayed a pronounced pi-stacking interaction between the aryl ligand and an aromatic ring of the phosphine ligand, whereas this interaction was absent in the phenethyl intermediate. When pentene is substituted for styrene, the normal intermediate is favored over the branched intermediate.