Spotlight on Ligand Effects in 1,2,3-Triazolylidene Gold Complexes for Hydroamination Catalysis: Synthesis and Catalytic Application of an Activated MIC Gold Triflimide Complex and Various MIC Gold Chloride Complexes

Abstract

The control of catalytic properties through ligand design is at the heart of homogeneous catalysis. Herein we report on ligand effects in six 1,3,4-substituted 1,2,3-triazolylidene gold complexes as precatalysts for the intermolecular hydroamination catalysis of alkynes with amines. Mainly silver-free protocols have been followed for the synthesis of the complexes and for the catalytic reactions. All of the novel gold complexes have been fully characterized, one of them being, to the best of our knowledge, the first 1,2,3-triazolylidene-based mesoionic carbene (MIC) gold complex with a weakly coordinating second ligand. In contrast to expectations, the gold complexes bearing the most strongly electron donating MICs did not display the best conversion in catalysis. According to our investigations the stability of the complex is a determining factor in the present case. The MIC gold bistriflimide complex shows activity in hydroamination catalysis without the need for an activating additive.

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

“…However, exceptions to this general behavior have been observed. For example, the most strong electron-donating phosphines are not efficient in facilitating the hydroamination, and the same trend was recently found for the case of mesoionic carbene (MIC) ligands, although these observations may be ascribed to changes in the steric properties and/or stability of the catalyst concomitant to the changes in their electronic properties. In addition, the use of redox-switchable gold­(I) catalysts shows that the activity of the in situ oxidized catalysts outperforms the activity of their reduced forms .…”

Gold(I)‐N‐Heterocyclic Carbene Synthons in Organometallic Synthesis

“…In 2021, Sarkar and colleagues reported the synthesis of [Au(MIC)(NTf 2 )] complex 105 (Scheme 64), which was tested as catalyst in the hydroamination of phenylacetylene. [130] In 2014, the reactivity of [Au(IMes)(NTf 2 )] in transmetalation reaction with a tungsten carbene complex was studied by Fürstner and colleagues (Scheme 65A). [131] The reaction led to a gem-bimetallic complex (106 a) that is stable at r.t. in CH 2 Cl 2 solution for hours.…”

Ligand-Enabled Sustainable Gold Catalysis

“…Very recently, Sarkar and co-workers disclosed a methodology to access 1,3,4-substituted-1,2,3-triazolylidene–gold complexes, ( L16 - L20 )­AuCl, under silver-free conditions from triazolium tetrafluoroborates L16 – L20 (Scheme ). These complexes showed good catalytic activity for the hydroamination of alkyne 39a with up to 930 TONs. Among all complexes, the L16 AuCl catalyst, bearing relatively strong electron donor and high steric demanding carbene, exhibited the highest activity.…”