Abstract
Gold(I) acetylide and σ,π-digold(I) alkyne complexes derived from one prototypical 1,6-enyne and from 7-ethynyl-1,3,5-cycloheptatriene have been prepared and structurally characterized. Their possible role in gold(I)-catalyzed cycloisomerizations has been studied by experiment and by DFT calculations. Gold(I) acetylides are totally unproductive complexes in the absence of Brønsted acids. Similarly, no cyclizations were observed by heating σ,π-digold(I) alkyne digold(I) at least up to 130 °C. Theoretical studies provide a rationale for the much lower reactivity of digold species in reactions of enynes.
Highlights
Digold(I) complexes have been known since the mid1970s,1 their relevance in homogeneous gold(I) catalysis has only been recognized recently.[2−4] They display interesting luminescence properties and are important building elements for the design of supramolecular structures.[5]
Gold(I) acetylide and σ,π-digold(I) alkyne complexes derived from one prototypical 1,6-enyne and from 7-ethynyl-1,3,5-cycloheptatriene have been prepared and structurally characterized
We examined the reaction of 7-ethynyl-1,3,5-cycloheptatriene (11), which reacts cleanly with A or B to give indene (12).[43]
Summary
Digold(I) complexes have been known since the mid1970s,1 their relevance in homogeneous gold(I) catalysis has only been recognized recently.[2−4] They display interesting luminescence properties and are important building elements for the design of supramolecular structures.[5]. Digold complexes 3 are excellent catalysts in reactions of diynes in which one of the alkynes is a terminal one, by allowing the simultaneous formation of a nucleophilic σ-alkynyl gold(I) species and an electrophilic π-alkyne gold(I) species, The experimental and computational data for the cyclization of allenynes such as 4 to form 5 suggested that σ,π-alkyne digold(I) intermediates 6 initiate a 5-endo-dig cyclization to form gem-diaurated species 7 and 8, which give rise to 5 by protodeauration This and related mechanisms have been recently reexamined by Fensterbank, Gandon, and Gimbert in the context of a broader study on the ligand and anion effects in the cycloisomerizations of allenynes.[35]. Catalyzed cycloisomerization reactions by isolating the corresponding gold(I) acetylides and digold complexes
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