Ligand effects in the rhodium-catalyzed addition of alkynes to aldehydes and diketones. Modification of the β-diketonate ligand

A catalytic amount of dicarbonylacetonato rhodium(I) and a phosphine ligand bearing bulky electron-donating alkyl groups has been shown to generate an effective catalyst for the addition of alkynes to aldehydes and activated ketones under mild, neutral conditions. While previous studies have shown that modification of the phosphine has significant effects on the activity of the catalyst, the role of the β-diketonate ligand has not been probed. Six different β-diketonate rhodium complexes were synthesized and their ability to catalyze the alkyne addition reaction was evaluated. Changing the structure of the β-diketonate ligand can have a noticeable effect on the reaction rate. Acetylacetonate derivatives with strong electron withdrawing groups have a detrimental effect on the catalytic activity, while bulky and electron rich β-diketonate derivatives provide more efficient catalysts.