Correlating the Activity of Rhodium(I)-Phosphite-Lariat Ether Styrene Hydroformylation Catalysts with Alkali Metal Cation Binding through NMR Spectroscopic Titration Methods

Alkali metal salts can affect both the activities and regioselectivities of alkene hydroformylation catalysts containing polyether-functionalized phosphorus-donor ligands; however, it is unclear whether these effects arise from direct alkali metal cation binding to the active catalysts. To gain more insight into these effects, a series of phosphite-lariat ether ligands derived from the alkali metal cation binding agents 2-hydroxymethyl-12-crown-4 and 2-hydroxymethyl-15-crown-5 have been prepared. Rhodium(I) complexes of these ligands have been evaluated as styrene hydroformylation catalysts in the absence and presence of a variety of alkali metal salts. The activities of catalysts containing phosphites derived from 2,2′-biphenol or 1,1′-binaphthol increased significantly (up to 92%) in the presence of alkali metal cations that are “moderately oversized” for archetypal binding to the crown cavity. When this criterion are not met, a decrease in the catalytic activity is observed upon addition of an alkali m...