Understanding Thermal and Photochemical Aryl–Aryl Cross‐Coupling by the Au^I/Au^III Redox Couple

Abstract

Systematic mechanistic investigations of the gold(I)/gold(III) redox-controlled aryl-aryl cross-coupling reaction have been performed by using both a thermal and photochemical approach. Electron-deficient and electron-rich arenes were considered as the coupling partners of the reaction. Based on transition-state modeling and distortion/interaction analyses, it is shown that Au prefers to react with electron-deficient arenes whereas Au likes to activate electron-rich arenes. This orthogonal reactivity of gold makes it an efficient catalyst for the aryl-aryl cross-coupling reaction. The crucial role of the carboxylate ligand in the reaction has been elucidated through analysis of the transition states. It is shown that due to the presence of two coordination sites, a carboxylate ligand can stabilize the transition state more efficiently than other monodentate ligands such as chloride (Cl ). Moreover, carbon-boron transmetalation is shown to be favorable over direct C-H metalation, hence reactions initialized by C-B transmetalation are expected to be much faster and selective. Additionally, a dual photoredox/gold catalyst was employed to access the Au /Au catalytic cycle for the cross-coupling reaction. [Ru(bpy) ] was used as the photoredox catalyst for the reaction, which, on excitation, transfers an electron to one of the coupling partners, namely a diazonium salt (ArN ), and initializes the cycle.

Explaining the Advantageous Impact of Tertiary versus Secondary Nitrogen Center on the Activity of PNP‐Pincer Co(I)‐Complexes for Catalytic Hydrogenation of CO2

“…We envisage that the energy costs associated with structural distortions in the catalyst geometry have a significant contribution to the computed activation energy barriers. In order to gain further insights, this contribution (denoted as distortion energy or E d ) is quantified for each intermediate/TSs under the framework of the distortion‐interaction model, which has been successfully used to analyze and understand chemical reactivity in previous computational studies [40–42] . E d is computed as the difference between the electronic energies of the ground state geometry of the catalyst with the corresponding distorted geometry in the intermediate/TSs.…”

Metallaphotoredox: The Merger of Photoredox and Transition Metal Catalysis

“…While outside the scope of this Review, a number of transformations and mechanistic studies 359 have detailed the direct excitation of gold complexes in the absence of a photocatalyst. The chain mechanism suggested for many of the above transformations has led chemists to question the need for a dedicated photocatalyst, with numerous mechanisms possible for the direct activation of substrates by photoexcited gold.…”

Gold‐Catalyzed Cross‐Coupling Reactions: An Overview of Design Strategies, Mechanistic Studies, and Applications

“…[275,276] Based on stoichiometric experiments, Fouquet et al have further investigated the mechanismsf or the cross-coupling of arylboronic acids with aryldiazonium salts and used the methodologies for enantioselective synthesis of biaryls. [280,281] In ar ecent computational study, [282] Battacharjee and Datta unraveled the mechanistic details for the dual Au and photoredox promoted C aryl ÀHa ctivation and subsequentC aryl ÀC aryl cross-coupling reactions between electron-deficient and electron-rich arenes. [278] The direct cross-coupling of unactivated arenes with aryl diazoniums alts throughC ÀHa ctivation was developed by Lee et al [277] Although the intermolecular cross-coupling has al imited substrate scope, the intramolecular version can produce av ariety of diaryl products under mild reactionc onditions.…”