title: Unexpected anion effect in the alkoxylation of alkynes catalyzed by N-heterocyclic carbene (NHC) cationic gold complexes.
abstract: The intermolecular alkoxylation of alkynes is the oldest application of cationic gold(I) catalysts; however, no systematic experimental data about the role of the anion are available. In this contribution, the role of the anion in this catalytic reaction as promoted by a N-heterocyclic carbene-based gold catalyst, [(NHC)AuX] (X=BARF(-) , BF4 (-) , OTf(-) , OTs(-) , TFA(-) , or OAc(-) ) is analyzed, through a combined experimental (NMR spectroscopy) and theoretical (DFT calculation) approach. The most important factor seems to be the ability to abstract the proton from the methanol during the nucleophilic attack, and such ability is related to the anion basicity. On the other hand, too high coordination power or basicity of the anion worsens the catalytic performance by preventing alkyne coordination or by forming too much free methoxide in solution, which poisons the catalyst. The intermediate coordinating power and basicity of the OTs(-) anion provides the best compromise to achieve efficient catalysis.
authors.affiliation: Dipartimento di Chimica, Fisica e Ambiente, Università di Udine, Via Cotonificio 108, I-33100 Udine (Italy).
authors.forename: Luca
authors.initials: L
authors.lastname: Biasiolo
authors.forename: Marina
authors.initials: M
authors.lastname: Trinchillo
authors.forename: Paola
authors.initials: P
authors.lastname: Belanzoni
authors.forename: Leonardo
authors.initials: L
authors.lastname: Belpassi
authors.forename: Vincenzo
authors.initials: V
authors.lastname: Busico
authors.forename: Gianluca
authors.initials: G
authors.lastname: Ciancaleoni
authors.forename: Angela
authors.initials: A
authors.lastname: D'Amora
authors.forename: Alceo
authors.initials: A
authors.lastname: Macchioni
authors.forename: Francesco
authors.initials: F
authors.lastname: Tarantelli
authors.forename: Daniele
authors.initials: D
authors.lastname: Zuccaccia
mesh_terms: D000480:Alkynes / Q000737:chemistry*; D000838:Anions / Q000737:chemistry; D002384:Catalysis; D002412:Cations / Q000737:chemistry; D056831:Coordination Complexes / Q000737:chemistry*; D006046:Gold / Q000737:chemistry*; D006571:Heterocyclic Compounds / Q000737:chemistry*; D008697:Methane / Q000031:analogs & derivatives* / Q000737:chemistry; D015394:Molecular Structure
chemical_list: D000480:Alkynes; D000838:Anions; D002412:Cations; D056831:Coordination Complexes; D006571:Heterocyclic Compounds; C030011:carbene; D006046:Gold; D008697:Methane
keywords: alkoxylation; anion effects; density functional calculations; gold catalysis; reaction mechanisms