Tetranuclear Dicationic Aurophilic Gold(I) Catalysts in Enyne Cycloisomerization: Cooperativity for a Dramatic Shift in Selectivity

Abstract

In comparison to mononuclear gold Lewis acid catalysts, digold complexes and dual-gold catalysis have illustrated a distinct and powerful potential for the activation of carbon-carbon multiple bonds. Herein, this concept is pushed further by designing novel tetranuclear gold(I) dicationic complexes structurally supported by strongly stabilizing constraint diphosphinoferrocenyl ligands and attractive closed-shell Au•••Au aurophilic interactions. The use of a molecularly-defined tetranuclear dicationic aurophilic gold(I) precatalyst for the selectivity-challenging cycloisomerization of low-substituted 1,6-enynes favors the formation with high selectivity of strained azabicyclo[4.1.0]hept-4-enes -even in the complete absence of activating/orienting substituents on alkyne and olefin reactive functions. This selectivity is not achieved by the reported phosphine-and carbene-stabilized mono-and dinuclear cationic gold(I) complexes, including the ones formed from the same ligands. More importantly this selectivity differs also from nanoparticles and heterogeneous gold catalysts reported to date. DFT studies correlated to experimental mechanistic investigations support an unprecedented "cluster-like" reactivity from polynuclear cooperation at the origin of this peculiar selectivity where the aurophilic interactions preexist, and preorganize, gold cluster reactive intermediates.

Gold(i) complexes bearing a PNP-type pincer ligand: photophysical properties and catalytic investigations

“…Analogous to other similar tetranuclear [(Ph 2 P) 2 Py]gold(I) compounds previously described by Echavarren and co-workers ([(Ph 2 P) 2 Py] = (2,6(diphenylphosphino)pyridine)), 8 both complexes show fluxional behavior. Therefore, the 1 H NMR spectrum of 3 shows two broad signals 1), 2.2366 (7); Au(2)-P(2), 2.2320 (6); Au(1)-Cl(1), 2.3078 (7); Au(2)-Cl(2), 2.3078(8); Cl(1)-Au(1)-P(1), 175.60(2); Cl(2)-Au(2)-P(2), 177.17(2).…”

“…3 Gold-based catalysis is another well-known application of this type of complex and is recognized as a popular topic in organic synthesis. 4 In particular, polynuclear gold(I) complexes with aurophilic contacts have received increasing attention since their cooperative properties and reactivity have been evidenced in a variety of catalytic processes (Scheme 1): 5 (i) cycloisomerization of low-substituted 1,6-enynes; 6 (ii) intramolecular hydroamination of a urea-functionalized alkyne; 7 (iii) carbonylation of primary amines to form ureas; 8 and (iv) oxidative heteroarylation of alkenes. 9 Taking these precedents into consideration, we decided to synthesize di-and tetranuclear gold(I) complexes bearing the 2,6-bis(diphenylphosphinomethyl)pyridine ligand (DPPMPY) in order to study the impact of the flexibility of the ligand on the structural features of the gold complexes and their lumine- † Electronic supplementary information (ESI) available.…”

“…Gold-based catalysis is another well-known application of this type of complex and is recognized as a popular topic in organic synthesis. 4 In particular, polynuclear gold( i ) complexes with aurophilic contacts have received increasing attention since their cooperative properties and reactivity have been evidenced in a variety of catalytic processes (Scheme 1): 5 (i) cycloisomerization of low-substituted 1,6-enynes; 6 (ii) intramolecular hydroamination of a urea-functionalized alkyne; 7 (iii) carbonylation of primary amines to form ureas; 8 and (iv) oxidative heteroarylation of alkenes. 9…”

“…Hydrogen atoms and dichloromethane molecules are omitted for clarity. Selected bond distances (Å) and angles (°): Au(1)-P(1), 2.2366(7); Au(2)-P(2), 2.2320(6); Au(1)-Cl(1), 2.3078(7); Au(2)-Cl(2), 2.3078(8); Cl(1)-Au(1)-P(1), 175.60(2); Cl(2)-Au(2)-P(2), 177.17(2).…”

Regio- and Stereoselective Hydrochlorination/Cyclization of 1,n-Enynes by FeCl3 Catalysis

“…Many reactions had been developed to construct these frameworks, especially devoted to N-heterocycles . Among the well-known methods for obtaining these fragments, the cycloaddition of enynes is a powerful and stereoselective strategy for synthesizing them in terms of both atom economy and eco-compatibility. Metal-catalyzed hydrofunctionalization/cyclization of enynes has seen lengthy development since the pioneering work.…”