A Redox-Switchable Gold(I) Complex for the Hydroamination of Acetylenes: A Convenient Way for Studying Ligand-Derived Electronic Effects

Abstract

A gold complex with a naphthalene-di-imide-functionalized N-heterocyclic carbene (NHC) ligand was prepared and characterized. The electrochemical studies reveal that the complex is able to undergo two successive reduction events, associated to the reduction of the NDI moiety of the NHC ligand. Once the redox-switchable properties of this Au­(I) complex were proven, the complex was tested in the hydroamination of terminal alkynes. The activity of the neutral complex was moderate-to-high for this reaction, but the one-electron reduced species did not show any activity in the reaction. The activity of the catalyst could be toggled off and on several times by successively adding a reducing agent (cobaltocene) or an oxidant (acetylferrocenium tetrafluoroborate). The results indicate that the rate-determining step of the catalytic cycle is the nucleophilic attack of the amine on the Au-coordinated alkyne.

A redox-switchable catalyst with an ‘unplugged’ redox tag

“…2 a We recently described two NHC ligands fused to naphtalenediimide (NDI) and perylene-diimide (PDI) moieties that were coordinated to rhodium, iridium 5 and gold. 6 The presence of the NDI or PDI units appended to the NHC ligand allowed toggling between three levels of electronic control of the metal, and this was used for studying the redox-switchable catalytic properties of the complexes in the cycloisomerization of alkynoic acids, 5 a and in the hydroamination of alkynes. 6 In view of these previous results, we herein describe the preparation of a series of dimetallic rhodium and iridium complexes in which the two metals are bound by a NDI-di-propylene-di-imidazolylidene ligand.…”

“…6 The presence of the NDI or PDI units appended to the NHC ligand allowed toggling between three levels of electronic control of the metal, and this was used for studying the redox-switchable catalytic properties of the complexes in the cycloisomerization of alkynoic acids, 5 a and in the hydroamination of alkynes. 6 In view of these previous results, we herein describe the preparation of a series of dimetallic rhodium and iridium complexes in which the two metals are bound by a NDI-di-propylene-di-imidazolylidene ligand. Given that, apparently, the redox-active NDI unit is electronically disconnected from the two imidazolylidene groups due to the presence of the two n -propyl chains, it is expected that the modification of the oxidation state of the NDI core should impart little or negligible influence on the electron-donating ability of the two NHC units.…”

Hierarchical self-assembly of a radical naphthalenediimide-based N-heterocyclic carbene-Au(i) macrocycle

“…1,2 Organometallic supramolecular assemblies obtained by metal-carbene-directed self-assembly from N-heterocyclic carbene (NHC) ligands have been dramatically developed in stimulus-responsive organometallic materials, catalysis, and photochemical reactions. [3][4][5][6][7][8] This strategy utilizes the directional advantages of metal-carbene bonding to adequately control the design of various NHC-based supramolecular architectures. In the library of reported NHC complexes, a series of macrocycles, cages and other interlocked organometallic complexes have been constructed from coinage metals (Ag I , Au I , and Cu I ) and well-designed NHC ligands, binding in a fixed linear geometry.…”

Redox‐Switchable Complexes Based on Nanographene‐NHCs

“…In two recent studies, we showed how the fusion of a naphthalene diimide (NDI) moiety on the backbone of an Nheterocyclic carbene provided a ligand with redox-switchable properties, which was used for the preparation of rhodium and iridium catalysts for the cycloisomerization of alkynoic acids, [13] and in the preparation of gold(I) complexes for the hydroamination of alkynes. [14] The functionalization of the NHC ligands with the NDI core, allowed three levels of electronic control of the catalyst, given that the ligand can operate either in its neutral form, or in the one-or two-electron reduced forms of the NDI moiety, thus constituting a rare example of multistate redox switchable catalysis. We think that the scarcity of multi-state switchable catalysts is rather surprising, [15] given that multi-state switchable molecules feature prominently in molecular machines [16] and molecular electronics.…”