L‐Shaped Heterobidentate Imidazo[1,5‐a]pyridin‐3‐ylidene (N,C)‐Ligands for Oxidant‐Free Au^I/Au^III Catalysis

Abstract

In the last decade, major advances have been made in homogeneous gold catalysis. However, AuI/AuIII catalytic cycle remains much less explored due to the reluctance of AuI to undergo oxidative addition and the stability of the AuIII intermediate. Herein, we report activation of aryl halides at gold(I) enabled by NHC (NHC=N‐heterocyclic carbene) ligands through the development of a new class of L‐shaped heterobidentate ImPy (ImPy=imidazo[1,5‐a]pyridin‐3‐ylidene) N,C ligands that feature hemilabile character of the amino group in combination with strong σ‐donation of the carbene center in a rigid conformation, imposed by the ligand architecture. Detailed characterization and control studies reveal key ligand features for AuI/AuIII redox cycle, wherein the hemilabile nitrogen is placed at the coordinating position of a rigid framework. Given the tremendous significance of homogeneous gold catalysis, we anticipate that this ligand platform will find widespread application.

%VBur index and steric maps: from predictive catalysis to machine learning

“…The scope of %V Bur parameter covers the whole range of reactions, including hydrogenation, 31,32 oxidation, [33][34][35] crosscoupling reactions, 36 polymerization, 29,37,38 among others.…”

A laterally-fused N-heterocyclic carbene framework from polysubstituted aminoimidazo[5,1-b]oxazol-6-ium salts

“…Even when only considering gold catalysis [ 6 ], the ImPy framework has been used to great effect [ 7 ]. The motif has been used to introduce sterically demanding NHCs with secondary gold-ligand interactions [ 8 – 10 ], chiral environments [ 11 – 13 ] including those enabling secondary interactions with substrates for asymmetric catalysis [ 14 ], cooperative and bimetallic catalysis [ 7 , 15 ], and redox-enabling function for Au(I)/(III) cycles [ 16 – 17 ].…”

“…Even when only considering gold catalysis [6], the ImPy framework has been used to great effect [7]. The motif has been used to introduce sterically demanding NHCs with secondary gold-ligand interactions [8][9][10], chiral environments [11][12][13] including those enabling secondary interactions with substrates for asymmetric catalysis [14], cooperative and bimetallic catalysis [7,15], and redox-enabling function for Au(I)/(III) cycles [16,17]. Such L-shaped ligands provide scope to influence the reactivity profile of their resulting metal complexes through steric shielding, direct stabilising interactions with the metal, or by proximal effects to reactive species.…”

ItOct (ItOctyl) – pushing the limits of ItBu: highly hindered electron-rich N-aliphatic N-heterocyclic carbenes

“…As part of our program in transition-metal-catalysis, 8,9 herein we report the synthesis, structural characterization, and catalytic activity of I t Oct (I t Octyl) class of ligands, which are C 2 -symmetric, higher homologues of I t Bu (Fig. 1B, 2 ).…”