title: Carboxylate switch between hydro- and carbopalladation pathways in regiodivergent dimerization of alkynes.
abstract: Experimental and theoretical investigation of the regiodivergent palladium-catalyzed dimerization of terminal alkynes is presented. Employment of N-heterocyclic carbene-based palladium catalyst in the presence of phosphine ligand allows for highly regio- and stereoselective head-to-head dimerization reaction. Alternatively, addition of carboxylate anion to the reaction mixture triggers selective head-to-tail coupling. Computational studies suggest that reaction proceeds via the hydropalladation pathway favoring head-to-head dimerization under neutral reaction conditions. The origin of the regioselectivity switch can be explained by the dual role of carboxylate anion. Thus, the removal of hydrogen atom by the carboxylate directs reaction from the hydropalladation to the carbopalladation pathway. Additionally, in the presence of the carboxylate anion intermediate, palladium complexes involved in the head-to-tail dimerization display higher stability compared to their analogues for the head-to-head reaction.
authors.affiliation: Department of Chemistry, University of Illinois at Chicago, 845 West Taylor Street, Chicago, Illinois, 60607-7061 (USA).
authors.forename: Olga V
authors.initials: OV
authors.lastname: Zatolochnaya
authors.forename: Evgeniy G
authors.initials: EG
authors.lastname: Gordeev
authors.forename: Claire
authors.initials: C
authors.lastname: Jahier
authors.forename: Valentine P
authors.initials: VP
authors.lastname: Ananikov
authors.forename: Vladimir
authors.initials: V
authors.lastname: Gevorgyan
mesh_terms: D000480:Alkynes / Q000737:chemistry*; D002264:Carboxylic Acids / Q000737:chemistry*; D002384:Catalysis; D019281:Dimerization; D008958:Models, Molecular; D009941:Organomercury Compounds / Q000737:chemistry*; D010165:Palladium / Q000737:chemistry*; D013237:Stereoisomerism
chemical_list: D000480:Alkynes; D002264:Carboxylic Acids; D009941:Organomercury Compounds; D010165:Palladium
keywords: alkyne dimerization; carbopalladation; density functional calculations; hydropalladation; palladium