Hydroalkoxylation of Terminal and Internal Alkynes Catalyzed by Dinuclear Gold(I) Complexes with Bridging Di(N-Heterocyclic Carbene) Ligands

Elena Marcheggiani,Cristina Tubaro,Marco Baron,Andrea Biffis,Claudia Graiff

doi:10.3390/catal10010001

Elena Marcheggiani, Cristina Tubaro + Show 3 more

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https://doi.org/10.3390/catal10010001

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Abstract

A series of six dinuclear gold(I) complexes with bridging bidentate N-heterocycic carbene ligands (NHCs) of general formula Au2Br2LX (L = diNHC, X = 1–6) have been studied as catalysts in the intermolecular hydroalkoxylation of terminal and internal alkynes. The best catalytic results have been obtained by using Au2Br2L4, characterized by 2,6-diisopropylphenyl wingtip substituents and a methylene bridging group between the two NHC donors. Complex Au2Br2L4 has been structurally characterized for the first time in this work, showing the presence of intramolecular aurophiclic interaction in the solid state. In the adopted reaction conditions Au2Br2L4 is able to convert challenging substrates such as diphenylacetylene. Comparative catalytic tests by using the mononuclear gold(I) complexes AuIL7 and IPrAuCl have been performed in order to determine the possible presence of cooperative effects in the catalytic process.

Highlights

Gold catalyzed hydroalkoxylation of alkynes, first reported in the late nineties [1], is an interesting100% atom-economic reaction that allows for the preparation of vinyl ethers and acetals [2]
We have recently reported on the synthesis of a family of dinuclear gold(I) complexes of general
We2 Br have recently reported on the synthesis of a family of dinuclear gold(I) complexes of general formula Au

Summary

Introduction

Gold catalyzed hydroalkoxylation of alkynes, first reported in the late nineties [1], is an interesting. 100% atom-economic reaction that allows for the preparation of vinyl ethers and acetals [2]. This reaction is conveniently catalyzed by cationic gold(I) complexes of general formula AuL+ , usually prepared in situ, starting from the neutral species AuLX by halide abstraction with the silver AgY salt (Y = poorly coordinating anion) [3]. The resulting species in the reaction environment can coordinate the solvent molecule or the substrate. Ligand L is instead a spectator ligand that stabilizes the active form of the catalyst and modulates its steroelectronic properties. The reaction starts with the formation of the alkyne π-coordinated species

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