Exploring the Limits of π-Acid Catalysis Using Strongly Electrophilic Main Group Metal Complexes: The Case of Zinc and Aluminium

The catalytic activity of cationic NHC-Zn(II)and NHC-Al-III(NHC=N-heterocyclic carbene) complexes in reactions that require the electrophilic activation of soft C-C pi bonds has been studied. The former proved able to act as a soft pi-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 pi bonds but simple AlX(2)(+)ions were found potent in some cases.