1,2-Addition or Enolization? Variable Reactivity of a Cerium Acetylide Complex toward Carbonyl Compounds

The reactions of the cerium alkyne complex bearing 2,6-bis(dimethylamino)-4-methylphenolate supporting ligands (bdmmp) and a terminal acetylide moiety, Na[Ce(C CPh)(bdmmp)(3)] (1), with benzaldehyde and a family of enolizable ketones led to different products depending on the acidity of the parent carbonyl compound. The reactions of 1 with benzaldehyde, acetone, benzylideneacetone, or 1,1-diphenylacetone (pK(a)(DMSO) = 26.5-19.4) gave the products of nucleophilic addition of type Na[Ce(O-CR2-C CPh)-(bdmmp)(3)] featuring a new C-C bond. In contrast, the reaction of 1 with beta-tetralone (pK(a)(DMSO) = 17.6) resulted in the enolization and deprotonation of beta-tetralone with subsequent replacement of the acetylide ligand at the cerium ion by the enolate. Molecular structures for the cerium products were determined by X-ray diffraction studies, providing valuable information about the performance of organocerium reagents.