The catalytic activity of cationic NHC-ZnII and NHC-AlIII (NHC=N-heterocyclic carbene) 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 ZnX2 salts. The tested NHC-AlIII catalyst is not able to activate C-C π bonds but simple AlX2 + ions were found potent in some cases.
Keywords: NHC ligand; alkynes; aluminium; carbonyl-ene metathesis; cycloisomerization; zinc.
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