Unexpected Anion Effect in the Alkoxylation of Alkynes Catalyzed by N‐Heterocyclic Carbene (NHC) Cationic Gold Complexes |
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| Authors: | Luca Biasiolo Marina Trinchillo Prof Paola Belanzoni Dr Leonardo Belpassi Prof?Dr Vincenzo Busico Dr Gianluca Ciancaleoni Dr Angela D'Amora Prof Alceo Macchioni Prof Francesco Tarantelli Dr Daniele Zuccaccia |
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| Institution: | 1. Dipartimento di Chimica, Fisica e Ambiente, Università di Udine, Via Cotonificio 108, I‐33100 Udine (Italy);2. Dipartimento di Scienze Chimiche, Università Federico II di Napoli, Via Cintia‐ Complesso di Monte S. Angelo‐ 80126 Napoli (Italy);3. Dipartimento di Chimica, Biologia e Biotecnologie, Università degli Studi di Perugia, Via Elce di sotto 8, I‐06123, Perugia (Italy);4. Istituto di Scienze e Tecnologie Molecolari del CNR (CNR‐ISTM), Università degli Studi di Perugia, Via Elce di sotto 8, I‐06123, Perugia (Italy) |
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| 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. |
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| Keywords: | alkoxylation anion effects density functional calculations gold catalysis reaction mechanisms |
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