Exploring the Limits of π-Acid Catalysis Using Strongly Electrophilic Main Group Metal Complexes: the case of Zinc and Aluminum.

: The catalytic activity of cationic NHC-Zn(II) and NHC-Al(III) complexes in reactions that require the electrophilic activation of soft C-C π bonds has been studied. The former proved able to act as a soft π-Lewis acid in a variety of transformations. The benefit of the bulky IPr NHC ligand was demonstrated by comparison with simple ZnX 2 salts. The tested NHC-Al(III) catalyst is not able to activate C-C π bonds but simple AlX 2 + ions were found potent in some cases.